Normative values of semitendinosus tendon reflex latencies

OBJECTIVES: The semitendinosus tendon reflex (STR), also known as the medial hamstring reflex, is rarely described in literature and is believed to provide information mainly concerning the fifth lumbar spinal nerve (L5). Latencies can be obtained with clinical neurophysiological tests. Normative data for STR latencies are not available. The aim of this study was to provide normative values of STR latencies. Also we will describe the technique used for performing the tendon reflex measurements in a clinical neurophysiological setting. METHODS: To determine STR latencies, we measured the stimulus (tap with reflex hammer) – response (EMG activity associated with muscle contraction) relation. The stimulus was administered with a manually operated reflex hammer, tipped with electrically conductive rubber, triggering the EMG recording sweep on impact. The EMG response was recorded with surface electrodes placed on the skin overlying the semitendinosus muscle. RESULTS: Forty healthy subjects participated in the study. The group consisted of 18 women and 22 men with a median age of 30 years. The mean subject body height was 181 cm (SD 8.1). Latencies showed a significant correlation with body height (r = 0.70, R(2) = 0.48, P < 0.0001). The mean latency of the STR was 24.73 ms (SD 1.96). The rounded upper limit of normal of individual absolute right–left differences was 2 ms. CONCLUSION: We present, as far as we know, the first report on normative values of STR latencies. The STR could be elicited in 100% of our population. The left–right difference seems to be the most promising clinical parameter for diagnostic purposes. SIGNIFICANCE: We think our results can be of practical use for all clinical neurophysiologists/neurologists and may provide the basis for further research on test characteristics of STR latencies in patients with L5 radiculopathy.