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Discuss the relative contribution of muscle hypertrophy and neurological adaptations to the strength gains observed in response to a resistance training programme.

Resistance training or strength training is a type of exercise used to improve athletic performance, augment musculo-skeletal health and enhance body aesthetics. Resistance training is now adopted as an essential training component for a number of different athletes ranging from swimmers to soccer players, even endurance athletes (Wilmore and Costill, 1999). It is essential for strength and conditioning coaches to understand the mechanisms and processes involved in the development of strength for the successful implementation of appropriate and effective training programmes. Literature suggests that there are two main factors, which influence the role of strength development; hypertrophy and neurological adaptations. In general, muscle strength improves during the early phases of resistance training, with improvements in muscle size occurring later.  

Muscular strength is defined as the maximal force a muscle can produce in one contraction (Wilmore and Costill, 1999). Substantial improvements (25-100%) in muscle strength have been observed after just 3 to 6 months of resistance training. However, the physiological adaptations, which occur as a result of resistance training, differ significantly over time and as a result of the stimulus provided. Traditional theories suggested that improvements in strength were as a direct result of muscle hypertrophy. Hypertrophy refers to muscular enlargement, which will occur as a result of regular high-resistance activity after a few months training. There are two types of muscle hypertrophy, which can occur as a result of resistance training. In terms of this review, chronic hypertrophy will be discussed throughout and reflects actual structural changes to the muscle in terms of an increase in the number of muscle fibres or the size of existing fibres. In contrast, transient hypertrophy refers to fluid accumulation in the muscle as a result of a single bout of training.

Moritani et al. (1980) used electromyogram analysis the relative contribution of neural factors to increase muscle strength. Following 2 weeks of resistance exercise, the authors concluded that neurological adaptations accounted for 90% of the improvements found in muscular strength. In general, neural factors account for the majority of gains in maximal strength up until 8 weeks of training, after which, the percentage contribution of hypertrophy increases exponentially. In addition, Staron et al. (1994) used muscle biopsies to assess muscle fibre cross-sectional area following an 8-week, high intensity resistance training programme. Muscle strength improved substantially after 8 weeks of training, with the greatest gains occurring after only 2 weeks. The authors found that despite these improvements, biopsy results indicated only a minimal increase in the cross-sectional area of the muscle fibres, indicating strength gains were a result of neural adaptations and not fibre hypertrophy per se.

A substantial range of adaptations occur as a result of a resistance training programme, ultimately resulting in increased strength. An increase in the size of the active muscle, commonly termed hypertrophy, is seen as the long term adaptation to a resistance training programme, although hyperplasia may play a small part in this. There is a substantial weight of evidence to suggest a significant proportion of strength gains observed during the early phase of training is as a result of neurological adaptations. In principle, this increases the training stimulus to which the muscle is then exposed. It must be stressed that there are a number of confounding reports in the literature and although this seems like the most plausible explanation for the early development of strength when no change in muscle size is evident, the area remains ambiguous. Sports coaches and practitioners must understand the structural and functional developments of muscle as a result of strength training in order to develop specific programmes to suit each individual athlete. For example, research suggests that with the correct stimulus or strength programme, significant improvements in strength can occur without increased muscle mass. This may be particularly important for female athletes in particular who are often adverse to adding bulk or weight classification sports such as rowing or wrestling where increased strength would be beneficial but increased muscle bulk would be detrimental. This information is also important if the primary aims of the strength training programme is hypertrophy as it is apparent no increases in muscle size will be evident to begin with.

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