Fig 1.
Overview of the experimental protocol used in this study.
Maximal voluntary torque was measured pre-exercise, after VOL–1, VOL–2, and the end of the final contraction performed to exhaustion.
Table 1.
Pre-exercise muscle function and performance data during the 40% and 80% protocols.
All participants completed the VOL–1 workload without stopping. 3 out of 10 participants completed the second 30s contraction at 80% without stopping (VOL–1 to VOL–2). 6 out of 10 participants completed the second 60s contraction at 40% (VOL–1 to VOL–2) without stopping.
Fig 2.
EMG recordings showing the V-waves from a representative participant from vastus medialis (VM) and vastus lateralis (VL) measured pre and post the exercise protocols (40% and 80%).
V-waves are circled on the figures. Note the reductions in V-wave amplitude following the 80% protocol.
Fig 3.
Maximal voluntary torque (MVT), voluntary activation (VA, %), and quadriceps potentiated twitch torque (Q.pot.tw.max) measured during the 40% and 80% protocols.
MVT and Q.pot.tw.max are normalized to pre-exercise values. Main effect of time on MVT and Q.pot.tw.max. *** is p<0.001 from pre-exercise; # indicates interaction between time and protocol, with values reduced from VOL–1 and different from 80% protocol (p<0.01). Data are mean and SD.
Fig 4.
Voluntary rate of torque development (RTD) and rate of torque development of the quadriceps potentiated twitch (Q.pot.tw) from contraction (or twitch) onset.
Q.pot.tw was analyzed up to 75ms post onset as analysis up to 100ms would include the relaxation phase of the twitch. * is p<0.01 from pre-exercise. # is p<0.05 between protocols, indicating where interaction effects between time and protocol were observed. Data are mean and SD.
Fig 5.
Vastus lateralis (VL) and vastus medialis (VM) maximal EMG and V-waves (normalized to M-waves; EMG/M, V/M) for the 40% and 80% protocols.
# indicates interaction between time and protocol, with values reduced from pre-exercise and lower than the 40% protocol (p<0.05). Data are mean and SD.
Fig 6.
Rate of rise in vastus lateralis (VL) and vastus medialis (VM) electromyograms in time intervals from contraction onset.
Pooled results from both protocols are displayed. No time, protocol, or interaction effects were observed. Data are mean and SD.
Table 2.
Electromyograms (EMG normalized to M-waves; EMG/M, %) recorded from vastus lateralis (VL) and vastus medialis (VM) during the contractions performed at 80% and 40% maximal voluntary torque.
A main effect of protocol was observed for VL and VM (p<0.05).