Epidemiological studies confirm that in many occupations, workers are exposed to repetitive bending or lifting, a risk factor for the development of a neuromuscular disorder in the lumbar spine. This study focuses on assessing the effect that rest period duration between repetitive lumbar flexion periods has on the development of an acute neuromuscular disorder. If insufficient recovery time is allowed, the disorder could transition into a debilitating cumulative trauma disorder. Three experimental groups were subjected to 5-min, 10-min, and 20-min rest between six 10-min repetitive (cyclic) flexion periods. In all groups a 7 hour recovery period immediately followed the work/rest periods. Reflexive muscle activity, as well as load and displacement were measured over the working periods, as well as during the single cycle tests taken during the recovery period to assess the state of the tissues. These measurements were used to determine the creep present in the viscoelastic tissues in the lumbar spine, and assess the behavior of the neuromuscular response in the surrounding musculature. The results showed that the groups allowed 5-min and 10-min rest exhibited an acute neuromuscular disorder characterized by decreased reflexive muscle activity and muscle spasms during the working periods, and by the presence of delayed hyperexcitability of the muscles 3-4 hours into the recovery period. The intensity of the delayed hyperexcitability was greater in the group subjected to 5-min rest than in the group subjected to 10-min rest. In contrast, the 20-min rest duration group showed no delayed hyperexcitability. Residual creep in the lumbar spine was seen in all three experimental groups, as the viscoelastic tissues failed to return to their original lengths at the end of the 7 hour recovery period. Results imply that a work to rest ratio of 1:1 or higher may be a risk factor for the development of a neuromuscular disorder. The model developed indicated that it may take 2-3 days for the viscoelastic tissues in the lumbar spine to return to their original length. This indicates that once a neuromuscular disorder is induced, 2-3 days rest may be needed in order for the disorder to subside. Comparison of the results from this study to similar data using static flexion working periods shows that cyclic loading may be more deleterious than static loading, and require more rest in between working periods in order to prevent the onset of an acute neuromuscular disorder. Results from this study may be useful in developing work/rest schedules in the workplace in order to maximize productivity while protecting the health and safety of the worker.