MAGNITUDE PRODUCTION OF KNEE EXTENSOR TORQUE AND QUADRICEPS FEMORIS EMG DURING DYNAMIC CONTRACTIONS

Abstract

PURPOSE To examine knee extensor (KE) EMG, peak torque (PT) and work (W), as guided by perceived exertion (PE). METHODS Thirty subjects were evaluated for maximum KE strength, via isokinetic testing at 60 deg/s. Immediately following 5 maximal-effort contractions, subjects were instructed to “think about the feelings in their quadriceps during the contraction, and to assign a rating of 10 to those feelings”. Following 2 min of rest, subjects were asked to sit quietly and to “think about the feelings in their quadriceps and to assign a rating of 0 to those feelings”. Subjects then randomly performed 3 voluntary knee extensions, separately, at the following PE levels: 1, 2, 3, 4, 5, 6, 7, 8, and 9. For each contraction, subjects were instructed to “contract to a level that feels like a (assigned number)”. Peak torque and W were averaged over the second 2 contractions and normalized to the 3 highest values of the maximal efforts. Surface EMG, for the vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) muscles was sampled with 2 bi-polar sets of circular electrodes. Raw EMGs were full-wave rectified and integrated over the middle 1 s of knee extension for the second 2 contractions at each PE level, averaged across the 2 bi-polar pairs of electrodes for each muscle, and normalized to the EMG during the 3 highest MVCs. RESULTS Normalized KE PT and W increased significantly across PE levels 1–9. Peak torque and W over-production was observed at PE levels 1–2 and 1–3, respectively. Peak torque was statistically similar to equivalent %MVC values at PE levels 3–6, and PE levels 4–6 for W. At higher PE levels (7–9), over-estimation was observed. EMG of the VM, VL and RF increased significantly (p < 0.05), with relatively higher activation of the VL over the VM and RF muscles. CONCLUSION The major findings demonstrate attenuation of accurate KE torque replication at relatively high perceptual intensities, with a relatively greater reliance on the VL activation than VM.