Date Published: October 7, 2014
Publisher: Public Library of Science
Author(s): Lauren G. MacNeil, Elisa Glover, T. Graham Bergstra, Adeel Safdar, Mark A. Tarnopolsky, Guillermo López Lluch.
Concurrent exercise combines different modes of exercise (e.g., aerobic and resistance) into one training protocol, providing stimuli meant to increase muscle strength, aerobic capacity and mass. As disuse is associated with decrements in strength, aerobic capacity and muscle size concurrent training is an attractive modality for rehabilitation. However, interference between the signaling pathways may result in preferential improvements for one of the exercise modes. We recruited 18 young adults (10 ♂, 8 ♀) to determine if order of exercise mode during concurrent training would differentially affect gene expression, protein content and measures of strength and aerobic capacity after 2 weeks of knee-brace induced disuse. Concurrent exercise sessions were performed 3x/week for 6 weeks at gradually increasing intensities either with endurance exercise preceding (END>RES) or following (RES>END) resistance exercise. Biopsies were collected from the vastus lateralis before, 3 h after the first exercise bout and 48 h after the end of training. Concurrent exercise altered the expression of genes involved in mitochondrial biogenesis (PGC-1α, PRC, PPARγ), hypertrophy (PGC-1α4, REDD2, Rheb) and atrophy (MuRF-1, Runx1), increased electron transport chain complex protein content, citrate synthase and mitochondrial cytochrome c oxidase enzyme activity, muscle mass, maximum isometric strength and VO2peak. However, the order in which exercise was completed (END>RES or RES>END) only affected the protein content of mitochondrial complex II subunit. In conclusion, concurrent exercise training is an effective modality for the rehabilitation of the loss of skeletal muscle mass, maximum strength, and peak aerobic capacity resulting from disuse, regardless of the order in which the modes of exercise are performed.
Muscular adaptation to chronic exercise occurs to maintain cellular homeostasis during future bouts. Typically identified as one of two divergent modes, resistance or aerobic, exercise places stresses upon the myofibre that induce phenotypic changes that differ greatly between the modes. Through sets of low-repetition/high-intensity contractions, resistance exercise promotes hypertrophy and improves anaerobic energy supply, thereby increasing strength/short-term force generation , . Alternately, aerobic exercise is characterized by longer periods of high-repetition/low-intensity contractions that promote an increase in oxidative energy capacity, predominately through mitochondrial biogenesis and increased vascularization , improving fatigue resistance. However, these changes are not mutually exclusive as both modes modestly affect characteristics associated with the other –. It has been suggested that the adaptive processes may interfere with one another , , thereby attenuating the optimal adaptation that could be achieved from either mode individually. As such, training strategies for maximum improvement for a specific physical task, such as sport performance, should be designed with one of these endpoints in mind. However, the desired benefits of exercise may include improvements in both strength and aerobic capacity. For example, rehabilitation of changes that occur in skeletal muscle following disuse atrophy – and mitigation of the effects of aging ,  may require exercise programs utilizing both modes of muscle contraction.
Resistance and aerobic exercises are rehabilitation therapies used to regain losses in strength and aerobic capacity that typically occur during injury, illness or chronic disuse of skeletal muscle. Performing these exercises together in the same session as concurrent exercise typically increases both strength and aerobic function; however, some research suggests that interference in the signaling patterns for adaptation favor one phenotypic outcome, depending on the order in which the exercise modes are performed , . As such, we examined the effects of alternating the order of exercise in concurrent training protocols as a rehabilitation strategy for preferentially improving strength or aerobic capacity following 2 weeks of induced hypodynamia. Contrary to our hypothesis we did not find differences in the gene expression patterns, most protein content changes, and the increases in isometric strength or peak aerobic capacity between groups that completed concurrent exercise protocols in which the first mode was either endurance exercise or resistance exercise.
Concurrent exercise is an effective and efficient rehabilitation protocol for regaining lost strength and muscle mass associated with prolonged disuse. When performed immediately after one another, the order of exercise does not differentially influence the chronic mitochondrial enzyme activities changes or increases in maximum strength or aerobic capacity. Although the genes and most proteins we selected were not different between groups, adaptation to multimode exercise involves coordination of a myriad of unmeasured signaling pathways that may have been different. However, in the absence of an effect on performance any single difference may be acute or opposed by another. As a result, we have shown for the first time that concurrent exercise sessions provide a reproducible intervention for the clinical treatment of short term muscle atrophy. This is important as the translation of the adaptations following exercise interventions in health people to those in need of rehabilitation is questionable.