Introduction

Methods to improve sports performance is an ever-evolving practice for both the elite and non-elite. Resistance training is a very popular form of training used to improve sports performance due to the adaptations in hypertrophy, strength, power and speed. The physical changes amongst players exhibited in field sports such as rugby union over the last twenty years are very evident, with players today who are bigger, stronger and faster (Austin et al. 2011; Quarrie et al. 2013).

The search for increased muscle hypertrophy through the form of resistance training is very popular amongst players in field-based sports due to the strong correlations between muscle strength and muscle cross-sectional area (Maughan et al. 1983). Individual sports such as weightlifting, wrestling, boxing and other combat sports have also seen physical changes over the past few decades.

Unlike field-based sports, bodyweight category sports require the athletes to weigh in prior to the event taking place. The timing of the weigh-in can range anywhere from two to twenty-four hours before the event, depending on the sport in question and level of competition. However, like field-based sports, they exhibit a range of forces and velocities, so training to improve sports performance and the need to increase lean muscle mass and optimise body composition can be a major advantage (Siahkouhian M., Azimi F. 2016).

Optimal muscle hypertrophy is both directly and indirectly linked to improvement in all the sports mentioned above and this essay will look to review current research on the most up to date methods of developing hypertrophy through resistance training.

What is hypertrophy

The word hypertrophy refers to the increase in the size of muscle tissue or organ due to the enlargement of individual cells (Michael Kent 2007). Resistance training can generate adaptations that increase muscular hypertrophy due to the increased cross sectional area of skeletal muscle, myofilament density and changes in the fibre type (Folland & Williams 2007). There are two key factors that instigate hypertrophy responses as a result of resistance training; mechanical tension and mechanical stress (Shinohara et al. 1998).

Mechanical Tension

Mechanical tension (loading) produced by force generation and stretch leads to muscle fibre damage which is an important driver of the hypertrophy response (Pearson & Hussain 2015). There are two types of hypertrophy responses experienced following mechanical tension. The first is sarcoplasmic hypertrophy. This is the acute increase in muscle size experienced directly after resistance exercise, also known as the “pump” effect.

This is mainly due to an increase in various non-contractile elements and fluid inside the muscle which can disappear within a few hours. Although this appears to be non-functional, it initiates a process that involves the activation of protein-kinase signalling pathways in muscle influencing the hormonal profile by stimulating an anabolic environment (Schoenfeld 2010). The second form of hypertrophy is myofibrillar hypertrophy which can also be referred to as chronic hypertrophy. Myofibrils enlarge under mechanical stress and when they get to a certain size split to form two daughter myofibrils. This continuous process of increasing number of myofibrils increases the muscle fibres size.

The structural damage occurred to the myofibrils stimulates a response involving muscle protein synthesis. Protein balance, the difference between protein synthesis and protein breakdown, needs to be positive, for protein to be added to muscle fibres. Positive protein balance can only occur in the presence of amino acids which must be supplied from the breakdown of existing protein in the diet (Folland & Williams 2007).

Metabolic Stress

The accumulation of metabolites such as; lactate, hydrogen ion inorganic phosphate and creatine, build up during exercises. This process can be referred to as metabolic stress and carries equal weight to that of mechanical stress in the production of muscle hypertrophy (Loenneke & Pujol 2009; Schoenfeld 2013). A study comparing the metabolite accumulation between two groups, with both groups evenly matched in resistance exercise protocols, giving one group a thirty-second rest half way through a set compared to full completion of a set in the other group showed blood lactate levels to be significantly higher in the group with no rest.

The group with no rest also saw a significant increase in cross sectional area compared to the other group, demonstrating both and acute and chronic relationship between metabolic stress and muscle hypertrophy (Goto et al. 2005). It is theorised that mammalian target of rapamycin (mTOR) also plays a critical role in the regulation of skeletal muscle tissue through its involvement in the initial stages of protein synthesis. Evidence by Baar and Esser (1999) was the first of its kind which investigated the key role between phosphorylation and the increase in muscle mass.

Rapid activation of protein synthesis is partially inhibited by rapamycin, implying that mTOR, activated by amino acids, provides signals involving an increase in the translational capacity of the muscle cell through increased levels of ribosomes and other translational components (Wang & Proud 2006). Metabolic stress facilitates exercise induced muscle soreness (EIMS), elevated hormone production, increased fast twitch fibre recruitment, cell swelling, increased production of reactive oxygen species (Takarada et al. 2000; Schoenfeld 2013; Schiaffino et al. 2013; Pearson & Hussain 2015). The extent of EIMS experienced will be determined by the type of exercise selected, intensity, volume and duration of exposure.

Muscle damage can be both specific and general, enhancing muscle hypertrophy by releasing inflammatory agents, stimulating satellite cells and trigger the signalling pathways that upregulate insulin growth factor (Handayaningsih et al. 2011; Schoenfeld 2010; Schoenfeld 2012). Metabolic stress also causes a process of muscle fibre type transition. Muscle fibres types consist of slow twitch type I fibres and fast twitch type IIa and type IIx fibres.

The most common increases in fibres size during resistance training are to that of type IIa fibres at the expense of type IIx fibres. When examining muscle fibres through a muscle biopsy, studies have found fibre type transition to occur anywhere from six to fourteen weeks, depending on exercise selection, frequency, intensity and volume in the resistance training protocols used (Carroll et al. 1998).

Training Considerations

Appropriate application of training variables is essential for developing muscle hypertrophy responses. These include; exercise selection, training intensity, repetitions, training volume, training frequency and rest periods.

Exercise Selection

When designing a resistance training programme, one needs to look at the needs analysis of the athlete and sport. Exercise selection and order should be specific to the desired goal of the programme, adhering to the principals of dynamic correspondence, following a logical order in sequencing and stacking. Highly technical and neural demanding exercises should be completed in a fresh state, compound exercises that involve multiple muscle groups should be completed before isolation exercises and high-intensity exercises before low-intensity exercises (Siff 2003; Verkhoshansky & Verkhoshansky 2011).

Free weight compound exercises (multi-joint) are advantageous compared to isolation (single-joint) exercise due to the large range of motion they go through, using multiple muscle groups as a result of stabilisation requirements, consequently recruiting larger amounts of muscle fibres and a more significant anabolic hormone response post exercise, specifically in both testosterone and growth hormone levels, compared to that in isolation exercises (Hansen et al. 2001).

On the other hand, isolation exercises have their advantage in that they have a greater focus on a specific muscle group, which can serve a purpose if functional development is lacking or when rehabilitating from an injury in an underdeveloped muscle (Antonio 2000).

Training Intensity

Training intensity can be calculated as a percentage of ones one repetition maximum in the form of a load and is inversely proportional to the number of repetition one can complete. Finding the optimum intensity and load to use for muscle hypertrophy can be confusing due to the mixed findings amongst the literature available.

This is partly due to the inconsistency in volume and frequency among the studies as well as the training experience amongst the subjects used (Campos et al. 2002; Mitchell et al. 2012). Although it was previously generally accepted that loads needed to be at least sixty five percent (65%) of one’s repetition maximum to promote muscle hypertrophy responses (McDonagh & Davies 1984), recent research has emerged to show that low loads, ranging from thirty to fifty percent (30%-50%), can be an effective method to increase muscle hypertrophy amongst young well-trained men (Schoenfeld et al. 2015).

Repetition

Repetition range can be classified into low (1-5), moderate (6-12) and high ranges (13+), with each range having a different effect on the neuromuscular system through the use of different energy systems (Schoenfeld 2010). Moderate and high repetition ranges seem to be superior to that of low ranges due to the greater time under tension and metabolic stress associated with these ranges. Recent research seems to suggest the use of moderate repetitions (6-12) to be more advantages in developing muscle hypertrophy compared to low ranges (1-5) and high ranges (13+). This is believed to be the case because moderate repetitions recruit and fatigue the highest threshold of motor units attributing a greater anabolic dominance (Kerksick et al. 2009; Schoenfeld et al. 2016).

Training Volume

Training volume is calculated as the total number of reps, sets, and load combined. This is measured per exercises, training session, training week, training cycle, etc. High training volume (5 sets) has reliably proven greater hypertrophy adaptations when compared to that of moderate training volume (3 sets) and low training volume (1 set) when training intensity is standardised across all three (Krieger 2010; Wolfe et al. 2004). It is hypothesised that greater total mechanical tension, metabolic stress and muscle damage are a consequence of higher volume training leading to acute elevated testosterone levels and growth hormone response experienced after four sets compared to two sets

(Craig & Kang 1994; Mulligan et al. 1996; Smilios et al. 2003). A gradual increase in training volume over a training cycle appears to be most beneficial in maximising muscle hypertrophy. This accumulation of training volume should reach a peak overreaching point, followed by a short taper to allow for optimal supercompensation (Kuipers & Keizer 1988).

Training Frequency (100)

Training frequency refers to total the number of training sessions performed. Finding the optimal training frequency for muscle hypertrophy will depend on the factors discussed above as well as training experience. Low training frequency (2-3 days per week) has been proven to be effective for muscle hypertrophy amongst un-trained individuals (Berger 1962; Dudley et al. 1991; Hickson et al. 1994). However higher frequency (3+) appears to be more beneficial for muscle hypertrophy adaptation in advanced individuals as regular bouts of resistance exercise keeps elevated levels of muscle protein synthesis constant during the course of the week presuming appropriate measures are in place to prevent overtraining (Kraemer et al. 2002; Brad J Schoenfeld et al. 2015).

Rest Intervals

Rest intervals refer to the time taken to recover in between sets and exercises and can be classified into short (30 seconds or less), moderate (60-90 seconds) and long (120 + seconds) intervals, with each having a different effect on neural recovery, mechanical tension and metabolic stress (WILLARDSON 2006). Metabolic stress and metabolite build up are best affected during short rest intervals, however mechanical tension is compromised as it is best optimised during long rest intervals.

Hence moderate rest intervals provides the compromise between the two, enhancing a larger anabolic spike after exercise, whilst also allowing a greater chance of completion of repetitions, resulting in a higher overall training volume and greater muscle activation per set (Kraemer et al. 1990; Brad J. Schoenfeld et al. 2015; Willardson & Burkett 2006; Willardson & Burkett 2008).

Conclusion

Research over the past decade has highlighted the importance of population specificity when comparing results and drawing conclusions on the topic of optimal muscle hypertrophy adaptations in response to resistance training. With exercise selection, training intensity, repetition, volume, frequency and rest periods all providing pivotal pieces of the puzzle to elicit mechanical tension, metabolic stress and muscle damage to promote muscle hypertrophy.

Sami Dowling – APEC High-Performance Director

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