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The Magnitude of Peripheral Muscle Fatigue Induced by High and Low Intensity Single-Joint Exercise Does Not Lead to Central Motor Output Reductions in Resistance Trained Men.

Marshall PW, Finn HT, Siegler JC - PLoS ONE (2015)

Bottom Line: Greater reductions in maximal torque and rate of torque development were observed during the 40% protocol (p<0.05).Maximal central motor output did not change for either protocol.For the 40% protocol reductions from pre-exercise in rate and amplitude variables calculated from the Q.(pot.tw) between 66.2 to 70.8% (p<0.001) exceeded those observed during the 80% protocol (p<0.01).

View Article: PubMed Central - PubMed

Affiliation: Human Performance Laboratory, School of Science and Health, University of Western Sydney, Sydney, Australia.

ABSTRACT

Purpose: To examine quadriceps muscle fatigue and central motor output during fatiguing single joint exercise at 40% and 80% maximal torque output in resistance trained men.

Method: Ten resistance trained men performed fatiguing isometric knee extensor exercise at 40% and 80% of maximal torque output. Maximal torque, rate of torque development, and measures of central motor output and peripheral muscle fatigue were recorded at two matched volumes of exercise, and after a final contraction performed to exhaustion. Central motor output was quantified from changes in voluntary activation, normalized surface electromyograms (EMG), and V-waves. Quadriceps muscle fatigue was assessed from changes in the size and shape of the resting potentiated twitch (Q.(pot.tw)). Central motor output during the exercise protocols was estimated from EMG and interpolated twitches applied during the task (VA(sub)).

Results: Greater reductions in maximal torque and rate of torque development were observed during the 40% protocol (p<0.05). Maximal central motor output did not change for either protocol. For the 40% protocol reductions from pre-exercise in rate and amplitude variables calculated from the Q.(pot.tw) between 66.2 to 70.8% (p<0.001) exceeded those observed during the 80% protocol (p<0.01). V-waves only declined during the 80% protocol between 56.8 ± 35.8% to 53.6 ± 37.4% (p<0.05). At the end of the final 80% contraction VA(sub) had increased from 91.2 ± 6.2% to 94.9 ± 4.7% (p = 0.005), but a greater increase was observed during the 40% contraction where VA(sub) had increased from 67.1 ± 6.1% to 88.9 ± 9.6% (p<0.001).

Conclusion: Maximal central motor output in resistance trained men is well preserved despite varying levels of peripheral muscle fatigue. Upregulated central motor output during the 40% contraction protocol appeared to elicit greater peripheral fatigue. V-waves declines during the 80% protocol suggest intensity dependent modulation of the Ia afferent pathway.

No MeSH data available.


Related in: MedlinePlus

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.
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pone.0140108.g003: 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.

Mentions: There was a significant interaction between time and protocol for MVT (Fig 3; p = 0.001). MVT for both protocols was similarly reduced from pre-exercise by 21.4 ± 10.2% at VOL–1 (p<0.001). During the 40% protocol MVT at VOL–2 was reduced from VOL–1 by a further 23.5 ± 10.9% (p<0.001), but no further reductions were observed during the 80% protocol. An interaction between time and protocol was observed for RTD 0-100ms (p = 0.003) and RTDmax (p = 0.007). RTD 0-100ms and RTDmax were similarly reduced from pre-exercise at VOL–1 by 19.3 ± 24.7% and 21.3 ± 25.0% respectively (p<0.05). Further reductions were only observed during the 40% protocol, with RTD 0-100ms and RTDmax reduced by 64.1 ± 20.0% and 59.1 ± 16.7% respectively from pre-exercise after the final contraction (p<0.001). Main effects of time were observed for RTD in time intervals of 0–25, 0–50, and 0-75ms post-contraction onset (Fig 4; p<0.003). RTD 0–25, 0–50, and 0-75ms were reduced from pre-exercise after the final contraction by 36.2 ± 57.7%, 39.9 ± 51.4%, and 43.9 ± 40.9% respectively (p<0.05).


The Magnitude of Peripheral Muscle Fatigue Induced by High and Low Intensity Single-Joint Exercise Does Not Lead to Central Motor Output Reductions in Resistance Trained Men.

Marshall PW, Finn HT, Siegler JC - PLoS ONE (2015)

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.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4595208&req=5

pone.0140108.g003: 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.
Mentions: There was a significant interaction between time and protocol for MVT (Fig 3; p = 0.001). MVT for both protocols was similarly reduced from pre-exercise by 21.4 ± 10.2% at VOL–1 (p<0.001). During the 40% protocol MVT at VOL–2 was reduced from VOL–1 by a further 23.5 ± 10.9% (p<0.001), but no further reductions were observed during the 80% protocol. An interaction between time and protocol was observed for RTD 0-100ms (p = 0.003) and RTDmax (p = 0.007). RTD 0-100ms and RTDmax were similarly reduced from pre-exercise at VOL–1 by 19.3 ± 24.7% and 21.3 ± 25.0% respectively (p<0.05). Further reductions were only observed during the 40% protocol, with RTD 0-100ms and RTDmax reduced by 64.1 ± 20.0% and 59.1 ± 16.7% respectively from pre-exercise after the final contraction (p<0.001). Main effects of time were observed for RTD in time intervals of 0–25, 0–50, and 0-75ms post-contraction onset (Fig 4; p<0.003). RTD 0–25, 0–50, and 0-75ms were reduced from pre-exercise after the final contraction by 36.2 ± 57.7%, 39.9 ± 51.4%, and 43.9 ± 40.9% respectively (p<0.05).

Bottom Line: Greater reductions in maximal torque and rate of torque development were observed during the 40% protocol (p<0.05).Maximal central motor output did not change for either protocol.For the 40% protocol reductions from pre-exercise in rate and amplitude variables calculated from the Q.(pot.tw) between 66.2 to 70.8% (p<0.001) exceeded those observed during the 80% protocol (p<0.01).

View Article: PubMed Central - PubMed

Affiliation: Human Performance Laboratory, School of Science and Health, University of Western Sydney, Sydney, Australia.

ABSTRACT

Purpose: To examine quadriceps muscle fatigue and central motor output during fatiguing single joint exercise at 40% and 80% maximal torque output in resistance trained men.

Method: Ten resistance trained men performed fatiguing isometric knee extensor exercise at 40% and 80% of maximal torque output. Maximal torque, rate of torque development, and measures of central motor output and peripheral muscle fatigue were recorded at two matched volumes of exercise, and after a final contraction performed to exhaustion. Central motor output was quantified from changes in voluntary activation, normalized surface electromyograms (EMG), and V-waves. Quadriceps muscle fatigue was assessed from changes in the size and shape of the resting potentiated twitch (Q.(pot.tw)). Central motor output during the exercise protocols was estimated from EMG and interpolated twitches applied during the task (VA(sub)).

Results: Greater reductions in maximal torque and rate of torque development were observed during the 40% protocol (p<0.05). Maximal central motor output did not change for either protocol. For the 40% protocol reductions from pre-exercise in rate and amplitude variables calculated from the Q.(pot.tw) between 66.2 to 70.8% (p<0.001) exceeded those observed during the 80% protocol (p<0.01). V-waves only declined during the 80% protocol between 56.8 ± 35.8% to 53.6 ± 37.4% (p<0.05). At the end of the final 80% contraction VA(sub) had increased from 91.2 ± 6.2% to 94.9 ± 4.7% (p = 0.005), but a greater increase was observed during the 40% contraction where VA(sub) had increased from 67.1 ± 6.1% to 88.9 ± 9.6% (p<0.001).

Conclusion: Maximal central motor output in resistance trained men is well preserved despite varying levels of peripheral muscle fatigue. Upregulated central motor output during the 40% contraction protocol appeared to elicit greater peripheral fatigue. V-waves declines during the 80% protocol suggest intensity dependent modulation of the Ia afferent pathway.

No MeSH data available.


Related in: MedlinePlus