Molecular, neuromuscular, and recovery responses to light versus heavy resistance exercise in young men

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.

Keywords: Electromyography; mammalian target of rapamycin; postexercise recovery; resistance training.

Figure 1

Study design. Data collection procedures for each visit and the time between visits.

Figure 2

Subject fiber‐type data. (A) The number and percentage of fast‐ and slow‐twitch muscle fibers of each subject. (B) Two representative 20× objective images of subject 6 and subject 10.

Figure 3

Volume load and repetition data. (A) Volume load (VL) differences between light and heavy load conditions. (B) Repetition number differences between light and heavy load conditions. All data are presented as mean ± SE (n = 15 per bar), and mean data are presented below each bar. * indicates a significant between‐condition difference (P < 0.05).

Figure 4

Electromyography data. (A) The difference between conditions in EMG amplitude means for each set. (B–E) The EMG amplitudes for each set (sets 1–4) expressed as a percentage of maximal voluntary isometric contraction during the initial rep, middle rep, and last rep of each set. All data are presented as mean ± SE (n = 11 per bar). * indicates a significant between‐condition difference (P < 0.05). † indicates set 4 > set 1 for 80% 1RM. ‡ indicates sets 2, 3, and 4 > set 1 for 30% 1RM.

Figure 5

Soreness, myoglobin, and isokinetic dynamometry data. (A) The change in soreness measured by algometry. (B) The change in serum myoglobin. (C) The percent change in peak torque at each velocity at POST and 48hPOST each condition, relative to PRE. All data are presented as mean ± SE (n = 10 per bar for serum myoglobin and n = 11 per bar for isokinetic dynamometry). (D–F) The relationship between the percentage of fast‐twitch fibers and percent change in peak torque at each velocity 48hPOST light RE, relative to PRE. * indicates a significant between‐condition difference (P < 0.05).

Figure 6

Muscle mRNA expression. (A–L) The fold change in each mRNA relative to PRE. All data are presented as mean ± SE (n = 13 per bar). θ indicates significant time effect whereby values were significantly greater than baseline regardless of load condition (P < 0.05); # indicates significant time effect whereby values were significantly less than baseline regardless of load condition (P < 0.05).

Figure 7

Muscle phosphoprotein expression. (A–E) The fold change in each phosphoprotein. All data are presented as mean ± SE (n = 13 per bar). Beneath each bar graph, representative images of the magnitude of fold change are pictured. (F, G) The relationship between p‐p70s6k expression at 15mPOST and 90mPOST each condition and the percentage of fast‐twitch fibers. # indicates significant time effect whereby values were significantly less than baseline regardless of load condition (P < 0.05).