Impact of Different Mechanical and Metabolic Stimuli on the Temporal Dynamics of Muscle Strength Adaptation

Abstract

Lambrianides, Y, Epro, G, Smith, K, Mileva, K, James, D, and Karamanidis, K. Impact of different mechanical and metabolic stimuli on the temporal dynamics of muscle strength adaptation. J Strength Cond Res 36(11): 3246–3255, 2022—A fundamental task in exercise physiology is to determine and ultimately improve the adaptations that take place in the human body, an integrated network of various physiological systems, for example, muscle, tendon, and bone. Investigating the temporal dynamics (time course) of adaptations in these diverse systems may help us gain new knowledge about the functioning of the neuromotor system in healthy and pathological conditions. The aim of this review was to explore the temporal dynamics of muscular strength adaptations in studies implementing a resistance training intervention. In addition, we categorized these studies under mechanical or metabolic stimuli to identify whether certain stimuli cause faster muscle strength gains. Searches were performed using PubMed and Google Scholar databases. The review comprised 708 subjects from 57 training groups within 40 studies that met the inclusion criteria. The results revealed that the mean time point of first significant increase in muscle strength of all studies was 4.3 weeks, and the corresponding increase was on average about 17%. A plateau in muscle strength increase (∼25%) was found to occur between weeks 8 and 12. Categorization into stimuli groups revealed that performing training in a hypoxic environment is likely to produce a leftward shift (∼25% increase at ∼2.8 weeks) in the dose-response relationship compared with blood flow restriction and supplementation. However, stimuli that cause faster muscle strength gains may also induce imbalanced adaptation between the muscle and the surrounding biological structures, potentially triggering a degradation in some parts of the network (i.e., leading to an increased risk of injury).

Evidence of different sensitivity of muscle and tendon to mechano‐metabolic stimuli

“…In the current study, MTU measurements were taken biweekly to create a more complete profile of the temporal dynamics of muscle and tendon adaptation to mechano‐metabolic stimuli. The timepoint of first significant muscle strength increase in both legs (W02 with an overall average increment of about 6%) as well as the slower rate of increment or plateau at the end of the 12‐week training program are in line with previous investigations using high mechanical loading or metabolic stress exercises 8 . However, in contrast to muscle, there is limited information about the time course of human tendon adaptation to mechano‐metabolic stimuli.…”

“…The timepoint of first significant muscle strength increase in both legs (W02 with an overall average increment of about 6%) as well as the slower rate of increment or plateau at the end of the 12-week training program are in line with previous investigations using high mechanical loading or metabolic stress exercises. 8 However, in contrast to muscle, there is limited information about the time course of human tendon adaptation to mechano-metabolic stimuli. To our knowledge, only Kubo et al 34 analyzed mechanical load exercise-related adaptive changes in human AT properties over time.…”

“…7 It is well established that muscle responds well to a variety of mechanical loading modalities when a specific overall training volume is exceeded without the requirement to incorporate high training loads. 8 For example, it has been shown that muscle protein synthesis rate, muscle volume, and strength increase in a similar manner with exercise that reaches volitional (muscular) failure under both low and heavy loading (i.e., 30% vs. 80% of maximal strength). 9 The effect of such muscular contractions to failure on muscle strength gains is supported by evidence from studies which observed the accumulation of by-products such as lactate, hydrogen ions, 10 inorganic phosphate, and mitogen-activated protein kinase, all of which may induce an anabolic signal and hence muscle hypertrophy.…”

“…Morphological adaptations include predominantly increased muscle thickness and pennation angle, both yielding changes in physiological cross‐sectional area 7 . It is well established that muscle responds well to a variety of mechanical loading modalities when a specific overall training volume is exceeded without the requirement to incorporate high training loads 8 . For example, it has been shown that muscle protein synthesis rate, muscle volume, and strength increase in a similar manner with exercise that reaches volitional (muscular) failure under both low and heavy loading (i.e., 30% vs. 80% of maximal strength) 9 .…”