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Spinal loading contributes to low back pain

This is an excerpt from Ergonomics in Sport and Physical Activity by Thomas Reilly.

Many types of physical activity, whether in recreational or occupational contexts, have a high prevalence of back pain. Common among these is loading on the spine, irrespective of whether imposed by manual handling, weightlifting and carrying, twisting, or working too long in an inappropriate posture.

Golf is a recreational activity in which players carry their golf clubs around the course. Wallace and Reilly (1993) simulated an 18-hole round of golf in a laboratory study. Three conditions investigated were walking the course without playing, walking and playing (without bag), and walking and playing carrying an 8 kg golf bag. The walking condition caused a smaller spinal shrinkage (3.58 mm) than did playing (4.98 mm) and playing combined with carrying the golf bag (5.82 mm). It was suggested that the high incidence of low back pain in golf players may be associated not only with compressive loading but also with high shear forces produced during the golf swing.

Spinal loading is implicated in back injury in cricket. Reilly and Chana (1994) used spinal shrinkage to identify specific consequences for the spine of fast bowling. Bowling every 30 s for 30 min caused shrinkage of 2.30 mm compared with 0.29 mm when a run-up without a delivery was used. The delivery rather than the run-up was found to be the main cause of spinal shrinkage in cricket bowling. A gravity inversion regimen preexercise was found to have a likely protective role in such practice conditions.

Field invasive games such as hockey make unique physiological and physical demands on players. Playing and dribbling the ball are usually executed in a position of spinal flexion. Evidence of the physical strain on the spine during field hockey was provided by Cannon and James (1984), who reported that over a 4-year period 7.6% of patients referred to a clinic for athletes suffering from back pain were hockey players. Reilly and Seaton (1990) observed an average shrinkage rate of 0.4 mm/min in players dribbling a hockey ball in a laboratory simulation, a value greater than previously reported for other activities. The investigators concluded that the peculiar postural requirements of the game caused physiological strain (indicated by oxygen consumption and heart rate) and spinal loading in excess of orthodox locomotion. Later, Reilly and Temple (1993) demonstrated that an enhanced crouched position when dribbling accentuated the subjective and physical strain on the spine. Their observations suggested that the strength of the back muscles may have a protective function in such conditions.

Spinal shrinkage has been measured in occupational as well as sports contexts. In view of the responsiveness of spinal shrinkage to load carrying, the technique has been used to evaluate new mail-bag designs for postal deliveries. Parsons and colleagues (1994) compared three new designs with the existing pouch mail-bag in laboratory-based and field trials. The investigators based their assessments on spinal shrinkage combined with biomechanical, physiological, and perceptual (subjective) responses. The combination of techniques was useful in interpreting the overall results and in highlighting the particular benefits of the individual designs.

Many current guidelines for lifting in industrial work are tailored to static and sagittally symmetric postures, yet the majority of tasks associated with manual materials handling have asymmetric components. There is evidence that low back disorders are related to lateral bending, axial twisting, and awkward postures (Marras et al., 1993). Au and colleagues (2001) analyzed the spinal shrinkage attributable to repetitive exertions confined to each of the three separate axes (twist, lateral bend, flexion). The experiment was performed twice with small technique modifications in the twisting task (and thus two data collections were performed). Subjects performed each task for 20 min at 10 repetitions per minute, where stadiometer measurements of standing height were taken prior to and immediately following the 20 min exertion. The twisting task demonstrated significant spinal shrinkage (1.81 and 3.2 mm in the two experiments) but no clear effect emerged for the other two tasks. These data suggest that repetitive torsional motions impose a larger cumulative loading on the spine than do controlled lateral or flexion motion of tasks of a similar moment.

Musculoskeletal effects of aging can influence responses to compressive loading on the spine and its resultant shrinkage. Reilly and Freeman (2006) applied precision stadiometry to assess spinal shrinkage in a comparison of two age groups (18-25 and 47-60 years) completing a regimen of circuit weight training (2 sets of 12 exercises). The two groups showed a similar pattern of spinal shrinkage, loss in stature being greater for the first set compared with the second set. Subjects gained height when placed in the formal recovery posture, but responses were inconsistent during warm-up, cool-down, and active recovery. Irrespective of age, the spine was less responsive to loading as the duration of exercise increased. The authors concluded that, provided loading is related to individual capability, healthy older athletes are not necessarily compromised by their age in lifting weights.

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