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Muscle fibre activation is unaffected by load and repetition duration when resistance exercise is performed to task failure.
J Physiol 2019JP

Abstract

KEY POINTS

Performing resistance exercise with heavier loads is often proposed to be necessary for the recruitment of larger motor units and activation of type II muscle fibres, leading to type II fibre hypertrophy. Indirect measures [surface electromyography (EMG)] have been used to support this thesis, although we propose that lighter loads lifted to task failure (i.e. volitional fatigue) result in the similar activation of type II fibres. In the present study, participants performed resistance exercise to task failure with heavier and lighter loads with both a normal and longer repetition duration (i.e. time under tension). Type I and type II muscle fibre glycogen depletion was determined by neither load, nor repetition duration during resistance exercise performed to task failure. Surface EMG amplitude was not related to muscle fibre glycogen depletion or anabolic signalling; however, muscle fibre glycogen depletion and anabolic signalling were related. Performing resistance exercise to task failure, regardless of load lifted or repetition duration, necessitates the activation of type II muscle fibres.

ABSTRACT

Heavier loads (>60% of maximal strength) are considered to be necessary during resistance exercise (RE) to activate and stimulate hypertrophy of type II fibres. Support for this proposition comes from observation of higher surface electromyography (EMG) amplitudes during RE when lifting heavier vs. lighter loads. We aimed to determine the effect of RE, to task failure, with heavier vs. lighter loads and shorter or longer repetition durations on: EMG-derived variables, muscle fibre activation, and anabolic signalling. Ten recreationally-trained young men performed four unilateral RE conditions randomly on two occasions (two conditions, one per leg per visit). Muscle biopsies were taken from the vastus lateralis before and one hour after RE. Broadly, total time under load, number of repetitions, exercise volume, EMG amplitude (at the beginning and end of each set) and total EMG activity were significantly different between conditions (P < 0.05); however, neither glycogen depletion (in both type I and type II fibres), nor phosphorylation of relevant signalling proteins showed any difference between conditions. We conclude that muscle fibre activation and subsequent anabolic signalling are independent of load, repetition duration and surface EMG amplitude when RE is performed to task failure. The results of the present study provide evidence indicating that type I and type II fibres are activated when heavier and lighter loads are lifted to task failure. We propose that our results explain why RE training with higher or lower loads, when loads are lifted to task failure, leads to equivalent muscle hypertrophy and occurs in both type I and type II fibres.

Authors+Show Affiliations

Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.Department of Kinesiology, McMaster University, Hamilton, ON, Canada.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

31294822

Citation

Morton, Robert W., et al. "Muscle Fibre Activation Is Unaffected By Load and Repetition Duration when Resistance Exercise Is Performed to Task Failure." The Journal of Physiology, 2019.
Morton RW, Sonne MW, Farias Zuniga A, et al. Muscle fibre activation is unaffected by load and repetition duration when resistance exercise is performed to task failure. J Physiol (Lond). 2019.
Morton, R. W., Sonne, M. W., Farias Zuniga, A., Mohammad, I. Y. Z., Jones, A., McGlory, C., ... Phillips, S. M. (2019). Muscle fibre activation is unaffected by load and repetition duration when resistance exercise is performed to task failure. The Journal of Physiology, doi:10.1113/JP278056.
Morton RW, et al. Muscle Fibre Activation Is Unaffected By Load and Repetition Duration when Resistance Exercise Is Performed to Task Failure. J Physiol (Lond). 2019 Jul 11; PubMed PMID: 31294822.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Muscle fibre activation is unaffected by load and repetition duration when resistance exercise is performed to task failure. AU - Morton,Robert W, AU - Sonne,Michael W, AU - Farias Zuniga,Amanda, AU - Mohammad,Ibrahim Y Z, AU - Jones,Amanda, AU - McGlory,Chris, AU - Keir,Peter J, AU - Potvin,Jim R, AU - Phillips,Stuart M, Y1 - 2019/07/11/ PY - 2019/03/26/received PY - 2019/07/10/accepted PY - 2019/7/12/pubmed PY - 2019/7/12/medline PY - 2019/7/12/entrez KW - fatigue KW - load KW - protein signalling KW - surface EMG JF - The Journal of physiology JO - J. Physiol. (Lond.) N2 - KEY POINTS: Performing resistance exercise with heavier loads is often proposed to be necessary for the recruitment of larger motor units and activation of type II muscle fibres, leading to type II fibre hypertrophy. Indirect measures [surface electromyography (EMG)] have been used to support this thesis, although we propose that lighter loads lifted to task failure (i.e. volitional fatigue) result in the similar activation of type II fibres. In the present study, participants performed resistance exercise to task failure with heavier and lighter loads with both a normal and longer repetition duration (i.e. time under tension). Type I and type II muscle fibre glycogen depletion was determined by neither load, nor repetition duration during resistance exercise performed to task failure. Surface EMG amplitude was not related to muscle fibre glycogen depletion or anabolic signalling; however, muscle fibre glycogen depletion and anabolic signalling were related. Performing resistance exercise to task failure, regardless of load lifted or repetition duration, necessitates the activation of type II muscle fibres. ABSTRACT: Heavier loads (>60% of maximal strength) are considered to be necessary during resistance exercise (RE) to activate and stimulate hypertrophy of type II fibres. Support for this proposition comes from observation of higher surface electromyography (EMG) amplitudes during RE when lifting heavier vs. lighter loads. We aimed to determine the effect of RE, to task failure, with heavier vs. lighter loads and shorter or longer repetition durations on: EMG-derived variables, muscle fibre activation, and anabolic signalling. Ten recreationally-trained young men performed four unilateral RE conditions randomly on two occasions (two conditions, one per leg per visit). Muscle biopsies were taken from the vastus lateralis before and one hour after RE. Broadly, total time under load, number of repetitions, exercise volume, EMG amplitude (at the beginning and end of each set) and total EMG activity were significantly different between conditions (P < 0.05); however, neither glycogen depletion (in both type I and type II fibres), nor phosphorylation of relevant signalling proteins showed any difference between conditions. We conclude that muscle fibre activation and subsequent anabolic signalling are independent of load, repetition duration and surface EMG amplitude when RE is performed to task failure. The results of the present study provide evidence indicating that type I and type II fibres are activated when heavier and lighter loads are lifted to task failure. We propose that our results explain why RE training with higher or lower loads, when loads are lifted to task failure, leads to equivalent muscle hypertrophy and occurs in both type I and type II fibres. SN - 1469-7793 UR - https://www.unboundmedicine.com/medline/citation/31294822/Muscle_fibre_activation_is_unaffected_by_load_and_repetition_duration_when_resistance_exercise_is_performed_to_task_failure L2 - https://doi.org/10.1113/JP278056 DB - PRIME DP - Unbound Medicine ER -