Abstract
Recent evidence suggests that resistance training with light or heavy loads to failure results in similar adaptations. Herein, we compared how both training modalities affect the molecular, neuromuscular, and recovery responses following exercise. Resistance‐trained males (mean ± SE: 22 ± 2 years, 84.8 ± 9.0 kg, 1.79 ± 0.06 m; n = 15) performed a crossover design of four sets of leg extensor exercise at 30% (light RE) or 80% (heavy RE) one repetition maximum (1RM) to repetition failure, and heavy RE or light RE 1 week later. Surface electromyography (EMG) was monitored during exercise, and vastus lateralis muscle biopsies were collected at baseline (PRE), 15 min (15mPOST), and 90 min following RE (90mPOST) for examination of molecular targets and fiber typing. Isokinetic dynamometry was also performed before (PRE), immediately after (POST), and 48 h after (48hPOST) exercise. Dependent variables were analyzed using repeated measures ANOVAs and significance was set at P ≤ 0.05. Repetitions completed were greater during light RE (P < 0.01), while EMG amplitude was greater during heavy RE (P ≤ 0.01). POST isokinetic torque was reduced following light versus heavy RE (P < 0.05). Postexercise expression of mRNAs and phosphoproteins associated with muscle hypertrophy were similar between load conditions. Additionally, p70s6k (Thr389) phosphorylation and fast‐twitch fiber proportion exhibited a strong relationship after both light and heavy RE (r > 0.5). While similar mRNA and phosphoprotein responses to both modalities occurred, we posit that heavy RE is a more time‐efficient training method given the differences in total repetitions completed, lower EMG amplitude during light RE, and impaired recovery response after light RE.
Highlights
With regard to the acute molecular response to light versus heavy resistance exercise, Burd et al (2010) recently reported that the acute anabolic response to light (30% 1RM) unilateral knee extension RE to failure resulted in significantly greater myofibrillar fractional protein synthesis rates than heavy RE to failure (90% 1RM) 24 h postexercise, and that this response was potentially mediated through greater mechanistic target of rapamycin complex 1 signaling
Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society
The primary findings of this investigation can be summarized as follows: (1) no significant difference in total volume load between conditions occurred, the total number of repetitions required to achieve concentric repetition failure and time required in the light condition was significantly greater, (2) EMGAMP was significantly higher during heavy RE, while integrated EMG amplitude (iEMG) was significantly greater during light RE, and (3) functional leg extensor recovery was significantly dampened after light RE
Summary
A recent scientific debate has centered around whether training with relatively light versus heavy resistance training (RT) loads to repetition failure increases skeletal muscle hypertrophy and strength (Burd et al 2010, 2013; Mitchell et al 2012; Schuenke et al 2013; Jenkins et al 2016a; Morton et al 2016b). Recent reports have indicated that heavy and light loads yield similar strength-related outcomes (Morton et al 2016a; Jenkins et al 2017) In lieu of these findings, recent scientific debates have ensued questioning whether light and heavy resistance training facilitate hypertrophic and strength adaptations (Burd et al 2013; Schuenke et al 2013)
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