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Types of Resistance Training
This is an excerpt from Science and Development of Muscular Strength by Timothy J Suchomel.
Many resistance training methods may be used to enhance an individual’s strength characteristics. While each method has its own unique qualities, it is important for strength and conditioning professionals to understand the ability of each method to enhance an athlete’s peak and rapid force production. In addition, practitioners should be aware of the neuromuscular demand of each method because several are often prescribed concurrently. This section will provide an overview of various resistance training methods and highlight their potential benefits and limitations. With this knowledge, strength and conditioning professionals should be able to make educated decisions on which methods may best address the desired strength qualities of their athletes.
BODYWEIGHT EXERCISE
The use of bodyweight exercise, also known as calisthenics, dates to ancient Greece and the words kàlos (meaning “beauty”) and sthénos (meaning “strength”) (217). Exercises that fall under this umbrella include bodyweight squats, push-ups, pull-ups, sit-ups, and many others. It should be noted that although plyometric exercises (discussed later in this chapter) are often performed using only an individual’s body weight as resistance, they are prescribed for a different purpose and should thus not be grouped with traditional bodyweight exercises.
Bodyweight exercises are often closed-chain exercises that target multiple muscle groups and may increase the relative strength of individuals with less weight training experience (122). In addition, bodyweight exercises are often accessible and versatile in the sense that they may be performed in a variety of positions (e.g., traditional, wall, or feet-elevated push-ups). When bodyweight exercises are properly progressed, it may be possible to increase an individual’s strength (156). Due to the simplicity and versatility of these exercises, it is not surprising that individuals in the fitness industry have consistently ranked bodyweight exercise as a top 10 fitness trend since 2013 (304). However, regarding the physical preparation of athletes, bodyweight exercises often serve as an introductory form of resistance training before progressing to loaded exercises and more complex movements. For example, athletes may perform bodyweight squats before progressing to a goblet squat, front squat, or back squat.
The primary limitation of bodyweight exercise is the inability to consistently provide an overload stimulus to enhance maximal strength and force production (122). Simply, bodyweight exercises do not provide the opportunity to apply large magnitudes of force against one’s body mass. To increase or progress the intensity of a bodyweight exercise, one is limited to altering body position or increasing the number of repetitions. While the former may be effective with youth and adolescent athletes as well as those returning from injury, consistently increasing the number of repetitions may promote muscle endurance qualities rather than maximal and rapid force production characteristics. In fact, several studies have shown that prescribing more repetitions of the same exercise may not improve an individual’s strength characteristics (31, 175, 250, 307). Recognizing the benefits and limitations of bodyweight training may allow practitioners to implement this form of exercise more effectively.
Key Point
Bodyweight exercises often serve as an introductory form of resistance training before progressing to loaded exercises and more complex movements.
MACHINE-BASED TRAINING
It is quite common to see a wide variety of exercise machines within a commercial fitness setting. From a client and practitioner standpoint, this variety provides opportunities to target many muscle groups and the ability to use a variety of machines within the same training session. Compared to free weight training, machines may provide a safer alternative because the added resistance moves within a specific plane of motion and can be modified by pulley systems (cams), elastic material, hydraulics, or pneumatic resistance (241). In addition, machine-based exercises may provide the opportunity to isolate specific muscle groups, which may benefit tissue capacity development and injury rehabilitation (285). Whereas some researchers have shown that training with machine-based exercises may improve maximal strength to a greater extent than free weight training (241, 252), others have shown contrasting findings (236).
Machine-based exercises can include single-joint (e.g., knee extension) or multi-joint (e.g., leg press) movements. While single-joint exercises may isolate specific muscle groups to a greater extent than multi-joint movements, their ability to benefit strength characteristics that transfer to sporting movements may be questioned because few single-joint movements are performed in competition (14, 22, 215, 266). For example, single-joint exercises may improve strength; however, they may lack the coordinative pattern of sporting movements to improve the sport task itself (e.g., isolated plantar flexion and vertical jump performance) (58, 266). In contrast, multi-joint movements that involve several muscle groups may serve as a superior alternative to develop strength characteristics that transfer to sport (8, 23, 97, 266). Despite the potential of multi-joint, machine-based exercise to enhance the force production characteristics of individuals, it should be noted that free weight exercises recruit stabilization musculature to a greater extent (111, 182, 240, 266) and may thus place greater coordination and muscle recruitment demands on an athlete (285). Combined with the ability to increase free testosterone (241), free weight exercise may serve as a superior alternative to machine-based movements when the focus is developing greater peak and rapid force production characteristics that may transfer to sport.
ISOMETRIC TRAINING
Isometric exercises have been implemented in resistance training programs for decades. This method includes performing a muscle action in which the involved muscle lengths and joint angles do not change during each effort. Despite no measurable work being performed—due to the lack of displacement—isometric exercises (figure 5.1) may be effectively used to enhance the maximal and rapid force production characteristics of athletes (168, 171, 213, 214).
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Although single-joint isometric exercises such as knee extension (152), elbow flexion (59), and plantar flexion (168) have received attention within the scientific literature, several reviews (168, 171, 213, 214) and training studies (169, 170, 172) have highlighted various aspects of multi-joint isometric training. For example, researchers have shown that training with rapid, sustained isometric actions (3 seconds in duration) over 6 weeks produced greater isometric squat peak force adaptations compared with rapid, nonsustained isometric actions (1 second in duration) (169). The same research group also concluded that continuous inclusion of isometric squats for 24 weeks yielded greater maximal strength, sprint speed, and countermovement jump performance (172). Despite these findings, some may argue that isometric training lacks specificity when it comes to enhancing dynamic performance. However, it is important to consider that the force–time characteristics produced during isometric tasks may provide some insight into both upper- and lower-body dynamic performance. In this light, researchers concluded that peak force, as well as force produced at specific time intervals, during isometric tests may relate to various sport-specific performances, thus providing a rationale for their inclusion (171). The implementation of isometric exercises should not be overlooked due to the inclusion of isometric forces during a stretch–shortening cycle action (i.e., amortization phase). In theory, the ability to produce and sustain high magnitudes of force during this phase may allow athletes to “hold” higher braking (eccentric) forces and allow for greater early propulsion forces to be produced. Because of the potential to enhance peak force production and rate of force development characteristics (168, 171, 213, 214), practitioners may consider implementing said exercises during a resistance training phase that focuses on these qualities. However, it is important to consider the joint angle specificity of the isometric task and the positions in which an athlete may be during competition to promote effective transfer of training.
Strength and conditioning professionals should be aware that implementing isometric exercises with other exercises may provide a potentiation effect (see Potentiation Complexes later in this chapter). For example, various researchers have shown enhanced dynamic performances following different isometric exercise protocols (92, 96, 100, 110). Therefore, due to its simplicity and ability to train an athlete’s strength characteristics, practitioners may consider implementing isometric training into resistance training programs.
Key Point
Despite no measurable work being performed—due to the lack of displacement—isometric exercises may be effectively used to enhance the maximal and rapid force production characteristics of athletes.
KETTLEBELL TRAINING
Originally used as a measure of weight in the 1700s, the term kettlebell originates from the Russian word girya and refers to a cast-iron weight in the shape of a cannonball and handle (50). Before becoming popular in commercial gyms and strength and conditioning settings around the world, kettlebells were primarily used by the Soviet military in their physical preparation training. From a strength and conditioning standpoint, kettlebell training serves as another alternative to traditional barbell and dumbbell exercises (30).
Common kettlebell exercises include two- or one-handed swings, modified weightlifting exercises (e.g., one-arm snatch or clean), and Turkish get-ups. Although researchers suggested that kettlebell training may improve various measures of maximal strength (139, 140, 159, 174, 216) and vertical jump performance (159, 216), additional research showed contrasting findings for vertical jump (140) and sprint (132) performance. To youth and adolescent athletes with lower training ages, kettlebell training may serve as an effective stimulus to enhance both peak and rapid force production. However, kettlebell training may also be limited in its capacity to consistently provide an overload stimulus. For example, researchers have shown that training with weightlifting movements (i.e., high pull and power clean combined with the back squat) produced greater back squat and power clean maximal strength and vertical jump improvements compared to training with kettlebells (216). Simply, the amount of weight an athlete can traditionally perform a clean with will exceed the amount of weight the same athlete can use during a kettlebell swing performed with good technique. Professionals should also consider the size of the kettlebell’s handle and weight. For example, some commercial kettlebells weigh up to 109 kg (240 lb), and it is likely that the diameter of the handle will increase as the load increases. With the obvious limitation of grip for some athletes in this instance, strength and conditioning professionals must question whether there may be a more effective alternative.
Limited research has examined the long-term training effects of kettlebell training on an athlete’s strength characteristics. While some have sought to improve the implementation of these exercises (123), it is important that practitioners understand the limitations of kettlebells and program their use based on the desired strength characteristics that are being pursued. Although they may not serve as the primary training stimulus for healthy athletes, kettlebells may serve as effective training tools for athletes recovering from an injury (25). Furthermore, kettlebell exercises may serve as part of learning progression or regression for athletes, but also as alternatives or supplemental movements to traditional exercises to prevent monotony in training and by extension, an athlete’s desire to train.
BILATERAL AND UNILATERAL TRAINING
Bilateral exercises are those in which an external load is lifted with two limbs (e.g., back squat), whereas unilateral or partial-unilateral movements are defined as exercises in which the load is solely or primarily lifted by a single limb (figure 5.2) (183). While bilateral resistance is more commonly prescribed than unilateral training due to strong relationships between bilateral strength and general sport skills (e.g., jumping, sprinting, and change of direction [COD]) (286), the use of unilateral training often becomes a topic of debate within the strength and conditioning field. Proponents of the latter often cite that many movements in sport are performed unilaterally (e.g., sprinting, cutting); thus, some believe that training in this manner provides a greater degree of specificity and transfer. Interestingly, this may not be the case, because some researchers have shown greater adaptations to COD performance following bilateral versus unilateral training (11). These findings were supplemented by a 2021 meta-analysis that showed no differences between bilateral and unilateral training effects on short sprint and COD speed (192). Additional researchers indicated that similar improvements in bilateral and unilateral strength, sprint speed, and agility were shown after 5 weeks of either bilateral (back squat) and unilateral (rear-foot elevated split squat) training (260). Finally, Appleby and colleagues (10) showed that bilateral and unilateral training can improve movement-specific strength, but that each mode of training can transfer to the nontrained movement as well. Collectively, the existing literature supports the use of both bilateral and unilateral training; however, it has been suggested that strength and conditioning professionals should focus on the physiological stimulus rather than movement specificity when making programming decisions (11).
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Key Point
Collectively, the existing literature supports the use of both bilateral and unilateral training; however, it has been suggested that strength and conditioning professionals should focus on the physiological stimulus rather than movement specificity when making programming decisions.
An aspect of unilateral training that should not be overlooked when making programming decisions is the potential for increased muscle activation compared to bilateral movements. McCurdy and colleagues (184) showed greater gluteus medius, hamstring, and quadriceps muscle activation during a modified split squat compared to a traditional bilateral back squat. These findings are likely attributable to greater instability during unilateral exercises. While greater muscle activation may benefit muscle hypertrophy and strength, practitioners must consider the ability to load unilateral exercises safely. Simply, due to greater instability, a unilateral exercise cannot be prescribed with the same load as a bilateral exercise. As a result, bilateral exercises may provide a superior maximal and rapid force production stimulus due to their stability (19). Taking the research mentioned previously into account, strength and conditioning professionals should not exclude unilateral exercises but should instead prescribe them as assistance exercises to bilateral movements (227). Practitioners must also account for the additional volume that is associated with unilateral exercises because the number of repetitions may be doubled, assuming the athlete is performing the exercise with both limbs (e.g., 5 repetitions prescribed = 10 repetitions total). Due to the additional volume, unilateral exercises may be best implemented alongside bilateral exercises during preparatory phases of training that consist of higher training volumes. Obvious exceptions may include unilateral plyometric exercises during a strength–power phase of training.
STRONGMAN TRAINING
As discussed in chapter 1, strength competitions are rooted in the ability to lift various heavy objects. Strongman competitions have capitalized on this, and events include athletes lifting heavy loads for a maximum number of repetitions, carrying heavy loads for a given distance, or lifting a series of loads in the shortest amount of time possible (332). To prepare for the various events, strongman competitors may train using equipment such as loaded frames, stones, loaded sleds, logs, tires, sandbags, oversized dumbbells, and even some vehicles (331). While these pieces of equipment may allow for sport-specific training for strongman competitors, it should be noted that strength and conditioning professionals may use these objects as training tools with athletes who do not compete in strongman as well.
Researchers have shown that strongman training over a 7-week period may produce similar strength adaptations when compared to traditional resistance training (330). These findings may, in part, be due to the similar physiological demand placed on individuals during each method of training (121). It should, however, be noted that similar exercises performed using a strongman apparatus may not necessarily produce the same force production characteristics as a more traditional exercise. For example, Winwood and colleagues (328) showed that mean and peak vertical force production was similar between the strongman log exercise and the clean and jerk when performed at 70% of the participant’s 1RM clean and jerk; however, mean and peak power output during the clean and jerk was significantly higher than the log lift. In another study, researchers showed that the barbell push press exercise produced significantly greater braking force, propulsion force, and impulse compared to both small and large log push presses (232). In addition, the back squat was shown to produce significantly greater vertical forces, but substantially lower anterior forces compared with a heavy sprint-style sled pull (327). While the aforementioned studies provide strength and conditioning professionals with just three examples of comparisons, further biomechanical analyses of strongman exercises such as the atlas stones (126), yoke walk (127), sprint-style sled pull (147), and farmer’s walk (146) have also been completed. Because some strongman exercises may offer a novel training stimulus to athletes, additional research is warranted. Readers interested in further discussions of how to implement such exercises are directed to previous reviews (128, 329, 337).
BALLISTIC TRAINING
Exercises performed with ballistic intent (i.e., acceleration throughout the entire concentric phase of a movement), such as hexagonal barbell jumps and bench press throws, have been shown to produce greater magnitudes of power output than exercises that are nonballistic (272). Given that maximal strength (i.e., peak force production) and rapid force production underpin power output (298), it should not be surprising that ballistic exercise has been shown to produce greater maximal and rapid force, velocity, and power production as well as greater muscle activation compared to the same exercise performed quickly (160, 203, 292). Furthermore, researchers have shown that ballistic exercise may also allow for greater potentiation benefits to be realized compared to nonballistic exercise (246, 288, 289). This is likely due to the ability of ballistic exercises to lower the recruitment threshold of motor units (67, 308) and activate the entire motor neuron pool within milliseconds (78). As noted in chapter 3, the ability to recruit higher-threshold motor units favors large magnitudes of force being produced within a short duration, ultimately promoting favorable rapid force production adaptations. Therefore, it should come as no surprise that ballistic exercises are often prescribed for athletes throughout their careers; however, it may be important to consider the technical competency of individual athletes as well as their relative strength. For example, Cormie and colleagues (48) showed greater magnitudes of improvement in vertical jump performance with relatively stronger individuals following 10 weeks of training with jump squats. Further research showed greater improvements in jump squat velocity and net impulse in stronger participants compared to those that were weaker following combined weightlifting, plyometric, and ballistic training (137). In summary, ballistic exercises may serve as effective stimuli for desired strength adaptations; however, professionals must be selective when it comes to implementing these exercises with specific athletes and within resistance training phases throughout the year.
Key Point
Ballistic exercises may serve as effective stimuli for desired strength adaptations; however, professionals must be selective when it comes to implementing these exercises with specific athletes and within resistance training phases throughout the year.
PLYOMETRIC TRAINING
Plyometric exercises are rapid force production movements that include the stretch–shortening cycle in which an eccentric (lengthening) muscle action precedes a concentric (shortening) muscle action, with a brief amortization (i.e., isometric) period occurring between these phases. These exercises are unique in that they provide both a rapid braking stimulus and ballistic propulsion stimulus to the athlete. In fact, plyometric exercises may produce a series of adaptations benefiting an athlete’s strength characteristics. In a series of meta-analyses, researchers concluded that plyometric training has the potential to improve maximal strength (66, 218, 229) as well as vertical jump (176, 218, 229), sprint (64, 218), and COD performance (13). In addition, plyometric training has also been shown to alter muscle thickness, pennation angle, and fascicle length, which may lead to increased tendon stiffness (229), thus modifying an athlete’s force production characteristics. While much of the existing literature has focused on lower-body plyometric exercises, it is important to note that upper-body plyometric movements may also be implemented; however, they may not have as significant of an impact on an athlete’s strength characteristics (254).
Although plyometric exercises are meant to benefit the rapid force production characteristics of an athlete, they may lack the ability to enhance maximal force. Some researchers have sought to combat this problem by having participants wear weighted vests during plyometric training (148). Although their results showed positive squat jump, countermovement jump, and five jump adaptations, prescribing greater loads during plyometric exercises may diminish the original plyometric stimulus. For example, greater loads upon landing during a plyometric exercise may lead to greater braking forces, longer durations between the eccentric and concentric muscle actions, or both. Therefore, professionals are encouraged to prescribe plyometrics in a periodized fashion by manipulating the intensity of the exercises (9, 84, 88, 90, 138, 141, 155) and the volume of contacts (85, 89). Moreover, it is important to consider the length of the training program, frequency of training sessions, and athlete characteristics (e.g., relative strength, exercise competency). Examples of different plyometric exercises at varying intensities are displayed in figure 5.3. It should be noted that there is no optimal method of implementing plyometric training (228). An important consideration is whether plyometric exercises are being implemented in isolation or are complementing other forms of training (e.g., traditional resistance training, sprinting, conditioning). Although combined methods of training will be discussed later in this chapter, researchers have noted that plyometric training combined with traditional resistance training or weightlifting may lead to superior results compared to just one method on its own (65, 66).
WEIGHTLIFTING MOVEMENTS AND DERIVATIVES
Weightlifting movements such as the snatch, clean, and jerk and their derivatives (i.e., movements that are modified from the traditional competition lifts) have been consistently implemented by strength and conditioning professionals across a variety of sports and competitive levels (79, 82, 83, 86, 253). This is likely due to their ability to provide an effective overload stimulus during the rapid extension of the hip, knee, and ankle joints (i.e., triple extension). Moreover, these movements focus on moving light to heavy loads in a ballistic manner (273), likely producing favorable neuromuscular adaptations that benefit peak and rapid force production. Researchers have shown that weightlifting movements and their derivatives may provide a superior strength–power stimulus compared to traditional resistance training movements (12, 35, 36, 130), jump training (302, 306), and kettlebell training (216). A 2022 meta-analysis supports these findings for the improvement of an athlete’s strength characteristics (195). Although the aforementioned research has primarily focused on propulsive strength characteristics, researchers have shown that weightlifting movements may provide a unique braking stimulus as well (191). However, it is important to note that a spectrum of weightlifting movements and derivatives exists and that the exercise–load combination of these exercises, as well as the technical competency of an athlete, may modify the propulsion or braking stimulus received.
Key Point
Weightlifting movements and their derivatives may provide a superior strength–power stimulus compared to traditional resistance training movements, jump training, and kettlebell training.
Although the traditional weightlifting competition lifts (i.e., snatch and clean and jerk) may be prescribed in an athlete’s training program, derivatives (variations) of these lifts are often prescribed due to their decreased complexity (44). Weightlifting derivatives may be subdivided into catching, pulling, and overhead pressing derivative categories (table 5.1). Each is described next.
Catching derivatives modify either the starting position or catching position of the snatch or clean (43, 125, 269, 277, 299, 300, 301) and are often the most frequently prescribed weightlifting derivatives. As shown in the previous research, catching derivatives can be quite effective at improving an athlete’s peak and rapid force production characteristics. However, as with all methods of training, it is important to note that exercises exist on a spectrum and may not always provide an optimal training stimulus for an athlete.
Weightlifting pulling derivatives may modify the starting position of either a snatch or clean but also remove the catch phase of the lift (274). By removing the catch phase, athletes can focus on the rapid extension of the hip, knee, and ankle (plantarflexion) joints and potentially use loads in excess of a 1RM catching variation (45, 46, 112, 274, 287), thus promoting greater peak force adaptations. In addition, pulling derivatives such as the jump shrug (276) and hang high pull (275) may allow athletes to receive an effective rapid force production stimulus using light loads ([less than] 50% of the 1RM) with ballistic intent (150, 268, 270, 290, 291, 293, 296, 297). Interestingly, researchers have shown that individuals who train with weightlifting pulling derivatives may receive a similar (42) or greater (282, 283, 284, 291) strength–power propulsion stimulus compared to training with catching derivatives. Additional research has shown that the braking stimulus may be similar (47) or greater (280, 283) when training with pulling derivatives compared to catching derivatives; however, further research is needed in this area.
Finally, weightlifting overhead pressing derivatives are variations of the clean and jerk in which the clean is omitted and athletes typically lift the barbell off a squat rack, blocks, or stands before starting the movement (259). Less research has been completed on overhead pressing derivatives; however, these variations may provide athletes with an effective peak and rapid force production stimulus. Researchers have shown that athletes may be able to lift more weight during a jerk variation compared to a push press (256, 257); however, it is important to note that the technical competency of the athlete and the external load may alter the training stimulus (95, 258).
Collectively, weightlifting movements and their derivatives provide athletes with unique stimuli that may help them improve their peak and rapid force production characteristics. However, it is important to consider the training goals of an athlete and prescribe specific exercise–load combinations in order to achieve the desired adaptations (267).
POTENTIATION COMPLEXES
The term potentiation refers to the enhancement or increased potential of a given physical or physiological quality. Within a training method context, potentiation is typically realized as part of a complex (i.e., pairing) of two biomechanically similar exercises performed in succession. For example, a squat variation may be paired with a vertical jump (54, 288) or a bench press may be paired with a bench press throw (93, 149). Within these complexes, the goal is to enhance (potentiate) the performance of the latter exercise by using the former as a conditioning stimulus, often termed postactivation performance enhancement (PAPE) (56). An abundance of potentiation complexes have been examined within the scientific literature, with many researchers showing mixed findings (281). While the previous findings may be partially attributed to the design of the potentiation complex (e.g., exercise choice, volume–load, rest interval), researchers have shown that athlete characteristics—such as maximal strength—may have a significant impact on whether potentiation is realized (21, 37, 142, 190, 233, 244, 245, 289). Due to the influence that strength may have on PAPE, potentiation complexes have been classified as an advanced training tactic (285) and will therefore be discussed in greater detail in chapter 6.
VARIABLE RESISTANCE TRAINING
Large-muscle, multi-joint exercises such as the squat and bench press (and their respective variations) are commonly performed using eccentric and concentric muscle actions in which the load throughout the movement is constant. While prescribing exercises in this manner can certainly improve an athlete’s strength characteristics, the mechanical advantage or disadvantage of each muscle group may change throughout the exercise. Variable resistance training, also known as accommodated resistance training, modifies the external resistance of an exercise to maximize force production throughout the entire range of motion (94), using chains or elastic bands.
Researchers have shown that variable resistance training modifies the loading profile of an exercise (136), which allows athletes to overcome mechanical disadvantages at various joint angles (87, 317) by matching changes in joint leverage (336). This may allow athletes to train through sticking points, in which an athlete typically demonstrates a diminished ability to produce force. Although the prospect of overcoming mechanical disadvantages may seem appealing for novice athletes, the change in resistance throughout the movement may create unnecessary variation in an athlete’s technique, which may affect the athlete’s ability to express force. While some variation is necessary for novices to enhance skill acquisition (i.e., varied practice) (202), adding too much variation, such as modifying the load throughout each repetition before exercise technique is solidified, may have a negative impact on the coordination of the movement. Thus, to ensure that the athlete develops movement competency without additional variation and to allow for its use as a novel training method later in the athlete’s development, variable resistance training may also be classified as an advanced training method and will be discussed in greater detail in chapter 6.
ECCENTRIC TRAINING
Eccentric muscle actions are characterized by the forced lengthening of the musculotendinous unit due to greater resistive forces being applied compared to contractile forces being produced by the muscle (164). Published reviews have outlined the molecular and neural characteristics of eccentric muscle actions that may benefit an athlete’s mechanical function (i.e., maximal strength, rate of force development, and power output), morphological adaptations (e.g., muscle fiber cross-sectional area and fascicle length), and neuromuscular characteristics (e.g., motor unit recruitment and firing rate) and performance (e.g., vertical jump, sprint, and COD) (77, 294). While greater detail on the underlying mechanisms of strength is provided in chapter 3, it should be noted that chronic eccentric training may produce similar or greater force production training effects compared to concentric, isometric, or combined eccentric and concentric training (76). This is likely because individuals are 20% to 60% (131) or approximately 40% (211) stronger during eccentric actions compared to concentric actions. This, in turn, has allowed researchers to investigate loads up to 150% 1RM during the eccentric phase of an exercise (80, 115, 133). Despite a growing body of literature, more information is needed to fully understand eccentric muscle actions and their contribution to an athlete’s strength characteristics.
While training movements often consist of both eccentric and concentric muscle actions, an eccentric training stimulus places an emphasis on the eccentric phase through various means. For example, Mike and colleagues (189) discussed the use of the 2/1 technique (i.e., two limbs during the concentric phase, one limb during the eccentric phase), two-movement technique (i.e., compound exercise followed by isolation exercise), slow or superslow (i.e., tempo), and negatives with supramaximal loads ([greater than] 100% of the 1RM). Additional details on the eccentric training stimuli potential and implementation of tempo, flywheel inertial training (FIT), accentuated eccentric loading (AEL), and plyometric training methods is provided in a two-part review (294, 295). Finally, a 2022 review sought to classify different eccentric training methods by the speed of the eccentric muscle action (114). Although researchers have discussed the eccentric stimuli that may be produced with weightlifting catching and pulling derivatives (47, 191, 280, 283, 293), loaded jumps (161), eccentric cycling (41, 221), and COD drills (263), the following sections will focus on tempo, FIT, accelerated eccentrics, AEL, and plyometric training. The theoretical force production potential of each eccentric training method is shown in table 5.2.
Tempo
Perhaps one of the most common ways of providing an eccentric stimulus is by using tempo training, in which the duration of the lowering phase of a movement is increased (249). This method is often implemented using a submaximal load, whereby the concentric phase of the movement is performed with maximal intent following the prolonged eccentric phase. While the thought behind tempo training is to “overload” the eccentric phase of an exercise by increasing the time under tension, this method may be more suited for the development of muscular hypertrophy rather than strength (326). For example, researchers have shown that longer eccentric durations may lead to greater improvements in elbow flexor strength compared to shorter durations (151, 222); however, a much larger body of literature supports the notion that there are no favorable strength adaptations following longer eccentric tempos (15, 32, 99, 220, 243, 249, 265, 320, 323). It should be noted that most of the existing research has examined different eccentric durations using submaximal loading; thus, further research is needed using maximal or supramaximal loads when only the eccentric phase is performed, often termed negatives (189). Using tempo in this manner may allow for the recruitment of higher-threshold (type II) motor units and their associated fibers, whereas the use of submaximal loads may only stimulate Type I motor units, which may negatively affect the magnitude and rate of force production due to their slower contraction velocities (173).
Strength and conditioning professionals should be aware that longer tempos may negatively affect stretch–shortening cycle contributions to the magnitude and rate of force production. For example, Schilling and colleagues (237) demonstrated that purposefully slow durations reduce the potential for force production during resistance training movements. Moreover, researchers also showed reduced back squat (34) and bench press (34, 321) mean and peak barbell velocities during the concentric phase, decrements in countermovement jump height (243), and reductions in leg press rate of force development (265). Furthermore, the chronic use of longer eccentric tempos may increase perceived exertion (220), which may negatively affect overall training volume (98, 207, 322, 324) and intensity (325). Practically speaking, tempo training may be best implemented during resistance training phases that are characterized by higher training volumes and that emphasize the development of work capacity (295). Furthermore, while tempo training may affect muscle hypertrophy (15, 238, 326)—which can influence an athlete’s force production characteristics—there does not appear to be much support for the use of long eccentric duration tempo training for improving maximal or rapid force production characteristics. However, as previously noted, further research examining the use of maximal and supramaximal eccentric training is needed.
Key Point
While tempo training may affect muscle hypertrophy, there is limited support for the use of long eccentric duration tempo training for improving maximal or rapid force production.
Flywheel Inertial Training
Flywheel inertial training (FIT) is another eccentric training method that has gained popularity. This method uses inertial resistance that is produced from different inertial discs, rotational speed, and the characteristics of the device itself (209). Briefly, through the concentric phase of a predetermined range of motion, an athlete accelerates the tether or cord that is wound around a portion of the device before the energy created by the athlete must be accepted during the eccentric phase and the tether or cord is rewound. Although FIT devices were originally investigated as a gravity-independent training tool in 1994 (20), an abundance of research projects have since been conducted regarding their physical performance benefits. As part of a 2022 umbrella review, de Keijzer and colleagues (61) sought to summarize the existing FIT literature as it relates to strength development. The authors concluded that all the included existing systematic reviews and meta-analyses (6, 177, 210, 225, 231, 313) suggested that FIT may be effective for improving muscular strength; however, it should be noted that many of the included studies used single-joint exercises, which may not transfer as effectively to sport performance as multi-joint tasks. Moreover, despite the large volume of FIT studies, very few have compared the training effects to other forms of resistance training; thus, it cannot be concluded that FIT provides a superior training stimulus (230).
A basic search of the literature reveals the frequent use of the term eccentric overload, referring to the potential to create greater eccentric force production characteristics with FIT compared to traditional training. While some researchers have shown that the impulse characteristics of each repetition increase when using larger flywheels (33), others indicated that no eccentric overload was found when examining force–time characteristics (197, 209). The latter findings are supported by the notion that FIT devices generally provide a closed (isolated) system in which the athlete must accept the eccentric impulse created during the concentric phase of the movement (law of conservation of energy). As noted in chapter 1, the shape of the impulse determines the stimulus that an individual receives, which, in relation to FIT, may be determined by the eccentric technique used (61, 294, 303). For example, following a maximum concentric effort, the forces produced during the eccentric phase of a flywheel exercise may be low, moderate, or high depending on the strategy of the individual (294). Higher mean forces would indicate that the athlete would be using a stiffer strategy to stop the momentum of the flywheel, whereas lower mean forces would suggest that a compliant strategy was used (figure 5.4). It should be noted that an athlete may also stop themselves rapidly without descending the same distance, ultimately creating a high-force, short-duration impulse, which would require high rates of force production. However, the ability to use a compliant strategy may also be based on the relative strength of the athlete (295), which in turn may modify the stimulus received. Although certain devices have since been developed that use motorized technology to provide additional eccentric forces, many devices fail to include such a stimulus. However, researchers have shown that when performing assisted squats (e.g., pushing with the arms to create additional concentric acceleration, as seen with a Hatfield squat), the eccentric stimulus could be increased (334). Another form of assisted flywheel exercise is through the use of the 2/1 technique (157), as described previously. Readers interested in how an eccentric overload stimulus may be provided with flywheel exercises are referred to a 2024 review by Martínez-Hernández (179).
An additional consideration with FIT is its feasibility in training and the ability to effectively prescribe training intensities. Researchers concluded that the biggest perceived barriers to FIT implementation among therapists and professional soccer practitioners are equipment cost or space, evidence of effectiveness, and scheduling (62, 63). Simply, athletes and strength and conditioning professionals are more likely to be familiar with traditional exercises using free weight equipment rather than FIT devices. In this light, FIT devices may serve as a novel training stimulus to athletes; however, ecological validity is a valid concern, especially in a team setting. For the prescription of training intensities, it may be possible for strength and conditioning professionals to use movement velocity to track the intensity of FIT repetitions (33, 178). While this research is relatively new, it is important to investigate the potential differences between FIT exercises and traditional exercises using similar methods. Although the previous information outlined some of the existing literature on FIT, further information on the implementation of this training method can be found in several reviews (17, 18, 230).
Accelerated Eccentrics
Accelerated eccentric exercise requires athletes to perform the eccentric phase of a movement at an increased velocity that is the result of the eccentric execution strategy (114). Examples of these exercises may include both passive and active accelerated movements. Passive accelerated eccentrics require the athlete to perform the eccentric (braking) phase of a movement due to the downward acceleration caused from an external source (e.g., banded jumps). In contrast, active accelerated eccentrics are characterized by the athlete rapidly initiating the eccentric phase of an exercise before stopping (catching) the load in a certain position (e.g., hexagonal barbell drop catch; figure 5.5) (113).
The primary benefit of accelerated eccentrics is a rapid braking stimulus that may help athletes tolerate larger eccentric forces and benefit stretch–shortening cycle performance. Interestingly, despite being introduced as “accelerated powermetrics” by Verkhoshansky and Siff (312), minimal research has examined the effectiveness of this strategy. However, researchers have shown an increased eccentric demand (i.e., eccentric force, rate of force development, and impulse) during accelerated eccentric countermovement jumps (3) and drop jumps (1) compared to their traditional counterparts. It should be noted that propulsive phase characteristics were only improved during accelerated eccentric countermovement jumps, indicating that the difficulty of accelerated eccentric drop jumps may be too challenging for some athletes. This may be due to reflex inhibition in the presence of excessive eccentric loading (2). Van den Tillaar (309) demonstrated that higher forces are produced during a faster squat descent, thus providing the rationale for a loaded drop catch exercise. Unfortunately, no data exist regarding the longitudinal use of accelerated eccentric jumps or drop catches within training programs. Thus, although athletes may receive a rapid eccentric training stimulus acutely, the long-term training effects of accelerated eccentrics are unknown. Strength and conditioning professionals are therefore advised to interpret the existing findings with caution.
Accentuated Eccentric Loading
Another form of eccentric training has been termed accentuated eccentric loading or AEL. Although some have mistakenly classified FIT as AEL, this method requires that an exercise is performed using a heavier load during the eccentric phase compared to the concentric phase and that the movement is performed by pairing the eccentric and concentric phases with minimal disruption to the natural movement mechanics of the exercise (315). AEL has become a popular topic of investigation due to its unique ability to produce favorable strength adaptations (316) and the potential to use submaximal (247), maximal, and supramaximal loading (187, 271) combinations. However, due to the changes in load during the movement, potential for very heavy load prescriptions, and the influence of relative strength (188), AEL has been classified as an advanced training method (295). Thus, a further discussion of AEL will be provided in chapter 6.
Plyometric Training as an Eccentric Stimulus
Although plyometric exercises were discussed earlier in this chapter, it is important to acknowledge their potential as an eccentric training stimulus as well. For example, these exercises include a unique eccentric stimulus due to the speed of the muscle action that occurs during the first phase of the stretch–shortening cycle (294). Specifically, tasks such as landing may provide athletes with a training stimulus that may help them accept the forces created upon ground contact (162). Because the speed at which the eccentric phase occurs directly affects the eccentric stimulus, strength and conditioning professionals must consider the impact of their coaching cues (278, 279, 335) and the intensity of the plyometric exercise (9, 84, 88, 90, 138, 141, 155) when implementing these exercises. Thus, these exercises should be properly progressed based on the desired volume and intensity (85, 89) and the abilities of the athlete (295) to mitigate the potential for injury during repetitive landings (4, 60). Furthermore, while less literature has focused on the intensity and implementation of upper-body plyometric exercises (254), it is logical to progress these exercises using similar principles.
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