References
Muscle hypertrophy and its relevance to horses

Abstract
Muscle growth has been researched within human athletes to maximise muscle growth and performance; however, this area has been researched less for the equine athlete. Skeletal muscle growth predominantly happens by hypertrophy – the most common types are either myofibrillar or sarcoplasmic. There are a number of physiological processes involved in muscle hypertrophy, with muscle protein synthesis being one of the main contributors. The differentiation and proliferation of satellite cells also contribute to muscle growth, and the rates of these processes can be increased or decreased by the presence of different molecules. In human and animal studies, it has been found that muscle hypertrophy can be induced by regular training for several weeks, using targeted exercises, working on positive and negative gradients and the length and intensity of a training session.
Strength and conditioning programmes are essential for improving a horse's overall level of fitness; for reintroducing a horse back into work following an injury, general maintenance or improving fitness for competition. The fundamental importance of correct muscle development is widely understood and considered during the process of strength and conditioning training; however, the cellular and physiological detail is less commonly understood and addressed. Therefore, this review describes the process of muscle growth and looks at how published literature can be applied to maximise the efficiency of conditioning plans to achieve optimal muscle development.
There are three types of muscle: smooth, cardiac and skeletal. Smooth and cardiac muscles are controlled by involuntary neural stimulation. Skeletal muscle is controlled by conscious, voluntary neural stimulation and is responsible for movement (MacIntosh et al, 2006). Therefore, this review looks at the effect of exercise in general, as well as specific, targeted exercises, on skeletal muscle. Skeletal muscle is made up of several subunits – the smallest, sarcomeres, are a contractile unit made up of actin and myosin (Dave et al, 2022). Several sarcomeres are lined in series and in parallel to form myofibrils. Myofibrils are arranged to make muscle fibres, which subsequently become fascicles (Figure 1). The outermost outer layer of skeletal muscle is the epimysium, which is dense, irregular connective tissue (Jennings and Premanandan, 2017).
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