The effects of repetitive motion on lumbar flexion and erector spinae muscle activity in rowers
Introduction
Low back injuries are a significant problem in rowers (Howell, 1984; Reid et al., 1989; Hickey et al., 1997). The amount of lumbar flexion that occurs during the rowing stroke has been suggested (Reid and McNair, 2000) as a factor that might influence the possibility of a lower back injury. This suggestion is based primarily upon cadaveric research (Adams and Dolan, 1995) that has shown that an excessive amount of lumbar flexion can sprain ligamentous structures, and in combination with compression induce damage to intervertebral discs. There is only limited information available concerning the kinematics of the trunk and lumbar spine during the rowing stroke. For instance, Hosea et al. (1989) reported that the trunk moved from approximately 30° of flexion at the start of the drive phase (when the oar is placed in the water) to 28° of trunk extension at the finish of the drive phase. More recently, Bull and McGregor (2000) used electromagnetic sensors placed on the sacrum and the thoraco-lumbar junction to assess motion during rowing on an ergometer. Limited data (n=6) from graphs indicated that the sacrum was in a similar position to that of upright sitting at the start of the drive phase and thereafter rotated posteriorly between 30–40°. In respect to the thoraco-lumbar junction, at the start of the drive phase, between 20–25° of flexion compared to that recorded during upright sitting was recorded. Thereafter, during the drive phase, approximately 60° of extension was observed. While these studies provide useful information, for an appreciation of the potential for injury, the magnitude of lumbar flexion is needed (Adams and Dolan, 1991), particularly the amount of lumbar flexion that is occurring in respect to an individual’s total range of lumbar motion. It has been shown by Dolan and Adams (1993) that bending moments increase considerably as an individual approaches the limit of their range of lumbar flexion, and stress on spinal structures is increased. If a rower has relatively less total range of motion, then they may be operating closer to the elastic limits of their soft tissue structures (disc and ligaments), and hence be increasing the chance of injury. To date, this variable has not been measured during rowing.
A factor that might influence lumbar flexion levels is fatigue of the back extensor muscles. The primary forces that increase boat speed are generated by the legs (Lamb, 1989). However, the back extensor muscles play an important role, not only in generating force for increasing the velocity of the boat (Hosea et al., 1989), but also in regulating the amount of flexion and extension of the lumbar spine. If muscle fatigue occurs, it is possible that the lumbar range of flexion may increase, fatigue preventing the control of flexion particularly as the rower approaches the catch position where the blade is placed in the water. With increased lumbar flexion, the soft tissues structures of the spine will come under more stress for the reasons outlined above, and injury might be more likely to occur. The effect of fatigue has not been thoroughly investigated in rowing. Graphed data on a small number of subjects (n=6) in a study by Bull and McGregor (2000) provide some evidence that flexion does increase with fatigue. Further information is needed to confirm these findings.
Intuitively, for injury prevention programs to be most effective, they would be instituted as early as possible in an athlete’s career. Competitive rowing usually commences in the mid teenage years, and by the late teens an individual rowing in their school senior rowing team at the height of the season might be training twice daily for 4–5 days per week and covering 150 km per week. Given this volume of training, it is important that their technique is sound. Hence, in the current study, the focus was on competitive teenage rowers, the purpose being to examine lumbar flexion motion together with the electromyographic (EMG) activity from three selected erector spinae muscles across the drive phase of the rowing stroke, at three time points (20%, 60% and 95%) of a high intensity rowing trial.
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Subjects
In accordance with the Auckland University of Technology Ethics Committee requirements, rowers from two Auckland secondary schools were invited to participate on a voluntary basis. Written and verbal explanations of experimental procedures were provided and subjects and/or their caregivers gave written consent prior to testing. The subject group comprised eight females, aged between 15 and 17 years (mean: 16.4, SD: 0.7), and eight males aged between 15 and 16 years (mean: 15.9, SD: 0.3). In
Results
The mean and standard deviation for the degrees of lumbar curvature in erect standing and full flexion are presented in Table 1. The mean total range of motion for males and females was 52° and 53°, respectively. Fig. 2 shows the percentage of lumbar flexion utilised during drive component of the rowing stroke. At 20%, 60% and 95% of the trial, lumbar flexion remained relatively constant for the first 60% of the drive phase, and then between 60% and 100% of the drive phase lumbar flexion
Discussion
Few studies have quantified lumbar flexion or investigated the role of back muscles during the rowing stroke. These variables may influence the likelihood of a back injury, particularly when the rower is fatigued, hence the importance of gathering further information concerning the patterns of muscle activity and the range of lumbar flexion. Such information would be useful for injury prevention programs.
The mean total range of lumbar flexion from the standing position to full flexion was
Conclusions
The findings showed that the rowers attained relatively high levels of lumbar flexion during the drive phase of the rowing stroke, and these levels were increased during the duration of the trial. Furthermore, EMG activity in the selected lumbar extensors also increased to relatively high levels at the end of the trial. The observed decrease in the median frequency of these muscles’ EMG provided indirect evidence that muscle fatigue was occurring, and this observation may in part be responsible
Acknowledgements
The authors wish to acknowledge the Maurice and Phyllis Paykel Trust that provided funding that allowed this project to proceed.
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