Intrasession and intersession reliability of the quadriceps Hoffmann reflex

The Hoffmann reflex (H-reflex) is a resting electromyographic (EMG) measurement of motoneuron pool recruitment. While the soleus H-reflex has been studied extensively, the study of the quadriceps H-reflex has been limited for various reasons. To date no data exist regarding the reliability of this measurement within and between sessions over an extended period of time. The purpose of this study was to establish quadriceps H-reflex reliability over a four-week period consisting of 6 testing sessions. Eleven neurologically sound volunteers (age: 20 +/- 2 yr, height: 181.9 +/- 9.9 cm; mass: 84.2 +/- 17.8 Kg) participated in this study. Subjects were prepared for EMG surface electrodes over the vastus medialis and medial malleolus (ground). A stimulating bar electrode was placed over the femoral nerve, and a stimulus was delivered at 20 sec intervals with increasing amplitude to obtain a peak quadriceps H-reflex. Ten peak H-reflex measurements were recorded for each session. The stimulator amplitude was increased further to obtain the peak efferent motor response (M-response) for normalization of peak H-reflex measurements. The procedure was repeated at 1 hr, 24 hr, 1, 2, and 3 weeks following the initial session. Intraclass correlation coefficients (ICC (2.1) and ICC (3.1)) were calculated using normalized peak H-reflex measurements. Strong reliability was detected within a session (10 trials ICC (2.1) = 0.957, ICC (3.1) = 0.970; 5 trials ICC (2.1) = 0.961, (ICC (3.1) = 0.970). ICC (2.1) calculations yielded strong reliability between the first and second (1 hr) session (0.956) but moderate reliability between days 1 and 2 (0.787) and between all session over 4 weeks (0.756). ICC (3.1) calculations were also computed to determine the reliability for the fixed selection of sessions. This calculation yielded strong reliabilities between days 1 and 2 (0.969) and between all sessions over 4 weeks (0.911). Within a measurement session quadriceps H-reflex measurements are very reliable, and we recommend 5 trials to establish a measurement. Between measurement sessions these data provide evidence of strong reliability for these fixed sessions (ICC (3.1)), and generalized evidence for moderate reliability over a 4-week period has also been provided (ICC (2.1)). These data provide valuable information for the researcher and practitioner as to the reliability of this measurement in detecting changes in the neuromuscular system.