| The effects on nerve conduction measures of forceful exertion and repetitive movement with awkward wrist posture were examined with fifteen participants over 3 hours duration of exposure. Wrist workload was measured by using force resistance sensor and electrogoniometer, while the nerve conduction measures were recorded with TECA TD-20 EMG machine on before the start of the task and every 20 minutes thereafter, where the subject performed repetitive flexion/extension movements accompanied by intermittent pinch force exertion.;The results indicated that initial peak latencies (time = 0) were similar across workload conditions, however exposure to wrist workload over three hours of task performance produced a noticeable difference. Peak latencies for low force-low repetition (LOF.LOR), high force-high repetition (HIF.LOR), and low force-high repetition (LOF.HIR) conditions increased, while little change was found for high force-high repetition (HIF.HIR) condition. Regression analysis indicated that peak latency approached a reference value diagnostic of clinical evidence of carpal tunnel syndrome with 67 minutes of task performance, and 67 percent of participants had temporary peak latency increases beyond reference value under low force-low repetition (LOF.LOR) condition.;Thus, the high force-high repetition condition (HIF.HIR) results might be contrary to what would be expected, because full range of motions was not attained as supported by highly significant correlation between peak latency change and the range of motion. Also, temperature gain derived from rapid repetitive movements and highly forceful exertions may counteract the prolongation of peak latency, and mask the developing effect of carpal tunnel syndrome.;As expected, skin temperature had a profound effect on nerve conduction measures. After correction for skin temperature, temperature-corrected peak latency over time produced similar results to the measured peak latency.;Correlation analyses between workload variables and peak latency indicated that maximum wrist flexion, maximum range of motion, and cumulative exposure time had highly significant relationships with peak latency over time. Among these relationships, especially, the most interesting correlation was presented between cumulative exposure time of wrist F/E angle >30° and sensory nerve peak latency (r = 0.3715, p = 0.005), where peak latency increased as the cumulative exposure time increased. Regression analysis indicated that if wrist deviation repetitively exceeded 30° for over 125 minutes, sensory median nerve impairment may approach diagnostic clinical evidence of CTS. Thus, this relationship may be the most important output of this study, since peak latency change can be explained by cumulative time factor as well as wrist angular deviation factor, and it can be easily measured with the time interval when wrist is deviated over a threshold angle. In fact, the cumulative time of F/E angle >30° may serve as the best measure for investigating the effects of dynamic wrist workloads on the nerve conduction, hence the prevalence of CTS. |
