Physiological and Physical Adaptations within the Working Muscle Specific to Cardiovascular Training, Lactate Training, Adenosine Triphosphate-Phosphocreatine Training and Power Training

Abstract

Abbreviations: ATP-PC, adensosine triphosphatephosphocreatine; SSC, stretch shortening cycle IntroductionThe capacity for change within skeletal muscle is immense. Represented by gene expression on a molecular level, the alteration of muscle generally results in an increase or decrease in the amount of muscle proteins. When exercise stress is placed upon the skeletal muscle, the magnitude of adaptation is highly contingent upon plasticity of muscle. Thus, the Principal of Myoplasticity is the specific term that represents the capacity of muscle that is modifiable for adaptation and applies to the ensuing discussion related to muscular training adaptations. 1 Cardiovascular trainingCardiovascular training on a structural level elicits a significant increase in activation frequency of motor units and a slight increase in oppositional load against motor units. Quintessential cardiovascular training that presents this stimulus to the muscle is represented in weight bearing settings (i.e., running) as well as non-weight bearing settings (swimming and cycling). Cardiovascular training results in little to no effect on the crosssectional area of muscle and muscle fibers. However, specific to type I slow-twitch fibers, these fibers may experience slight increases in cross sectional size due to increases glycogen storage as well as oxidative metabolism.2,3 The majority of adaptations to skeletal muscle occur within the metabolic realm. The adaptations to muscle under the influence of cardiovascular training produce changes in fiber type, capillary supply, myoglobin content, mitochondrial function and oxidative enzymes. Fiber typeCardiovascular training relies primarily on type I, slow-twitch muscle fibers. In response to the volume and intensity of training, type I fibers have the capability to become larger in cross-sectional area. 2,4Fast-twitch fibers are not generally recruited to the same capacity as slow-twitch during cardiovascular training; therefore don't experience similar results in cross sectional area. Similarly, most literature suggests little change in muscle fiber percentage in slow-twitch and fast-twitch fibers; however, changes have been documented in fast-twitch subtypes. Type IIx fast-twitch fibers have called upon less during cardiovascular training, consequently, possess a lower aerobic capacity. Recent literature produced by the HERITAGE study suggests that type IIx fast-twitch fibers may transform to type IIa and it is even speculated they may be capable of transitioning to slowtwitch. However, very minuscule results have been published. Capillary supplyA significant adaptation to cardiovascular training is the increase in capillaries surrounding the muscle fibers. Literature has documented that cardiovascular trained individuals have significantly greater amounts of capillary density than compared to sedentary populations. 4,5 Dense capillary content allows a heightened interchange of gasses, heat, waste and nutrients between the working skeletal muscle and the blood delivered. AbstractObjecti...