Alun G. Williams

The adaptations to strength training : Morphological and neurological contributions to increased strength

AbstractHigh-resistance strength training (HRST) is one of the most widely practiced forms of physical activity, which is used to enhance athletic performance, augment musculo-skeletal health and alter body aesthetics. Chronic exposure to this type of activity produces marked increases in muscular strength, which are attributed to a range of neurological and morphological adaptations. This review assesses the evidence for these adaptations, their interplay and contribution to enhanced strength and the methodologies employed.The primary morphological adaptations involve an increase in the cross-sectional area of the whole muscle and individual muscle fibres, which is due to an increase in myofibrillar size and number. Satellite cells are activated in the very early stages of training; their proliferation and later fusion with existing fibres appears to be intimately involved in the hypertrophy response. Other possible morphological adaptations include hyperplasia, changes in fibre type, muscle architecture, myofilament density and the structure of connective tissue and tendons.Indirect evidence for neurological adaptations, which encompasses learning and coordination, comes from the specificity of the training adaptation, transfer of unilateral training to the contralateral limb and imagined contractions. The apparent rise in whole-muscle specific tension has been primarily used as evidence for neurological adaptations; however, morphological factors (e.g. preferential hypertrophy of type 2 fibres, increased angle of fibre pennation, increase in radiological density) are also likely to contribute to this phenomenon. Changes in inter-muscular coordination appear critical. Adaptations in agonist muscle activation, as assessed by electromyography, tetanic stimulation and the twitch interpolation technique, suggest small, but significant increases. Enhanced firing frequency and spinal reflexes most likely explain this improvement, although there is contrary evidence suggesting no change in cortical or corticospinal excitability.The gains in strength with HRST are undoubtedly due to a wide combination of neurological and morphological factors. Whilst the neurological factors may make their greatest contribution during the early stages of a training programme, hypertrophic processes also commence at the onset of training.

Specificity of Acceleration, Maximum Speed and Agility in Professional Soccer Players

High-speed actions are known to impact soccer performance and can be categorized into actions requiring maximal speed, acceleration, or agility. Contradictory findings have been reported as to the extent of the relationship between the different speed components. This study comprised 106 professional soccer players who were assessed for 10-m sprint (acceleration), flying 20-m sprint (maximum speed), and zigzag agility performance. Although performances in the three tests were all significantly correlated (p < 0.0005), coefficients of determination (r2) between the tests were just 39, 12, and 21% for acceleration and maximum speed, acceleration and agility, and maximum speed and agility, respectively. Based on the low coefficients of determination, it was concluded that acceleration, maximum speed, and agility are specific qualities and relatively unrelated to one another. The findings suggest that specific testing and training procedures for each speed component should be utilized when working with elite players.

Effects of differential stretching protocols during warm-ups on high speed motor capacities in professional soccer players

The purpose of this study was to examine the effects of different modes of stretching within a pre-exercise warm-up on high-speed motor capacities important to soccer performance. Eighteen professional soccer players were tested for countermovement vertical jump, stationary 10-m sprint, flying 20-m sprint, and agility performance after different warm-ups consisting of static stretching, dynamic stretching, or no stretching. There was no significant difference among warm-ups for the vertical jump: mean ± SD data were 40.4 ± 4.9 cm (no stretch), 39.4 ± 4.5 cm (static), and 40.2 ± 4.5 cm (dynamic). The dynamic-stretch protocol produced significantly faster 10-m sprint times than did the no-stretch protocol: 1.83 ± 0.08 seconds (no stretch), 1.85 ± 0.08 seconds (static), and 1.87 ± 0.09 seconds (dynamic). The dynamic- and static-stretch protocols produced significantly faster flying 20-m sprint times than did the nostretch protocol: 2.41 ± 0.13 seconds (no stretch), 2.37 ± 0.12 seconds (static), and 2.37 ± 0.13 seconds (dynamic). The dynamic-stretch protocol produced significantly faster agility performance than did both the no-stretch protocol and the staticstretch protocol: 5.20 ± 0.16 seconds (no stretch), 5.22 ± 0.18 seconds (static), and 5.14 ± 0.17 seconds (dynamic). Static stretching does not appear to be detrimental to high-speed performance when included in a warm-up for professional soccer players. However, dynamic stretching during the warm-up was most effective as preparation for subsequent high-speed performance.

The ACE gene and muscle performance

Angiotensin-converting enzyme in human skeletal muscle can be encoded by either of two variants of the ACE gene, one of which carries an insertion of 287 base pairs. This longer allele gives rise to lower enzyme activity, and is associated with enhanced endurance performance and an anabolic response to intense exercise training. Here we examine training-related changes in the mechanical efficiency of human skeletal muscle (energy used per unit power output) and find that the presence of this ACE allele confers an enhanced mechanical efficiency in trained muscle.

Similarity of polygenic profiles limits the potential for elite human physical performance

Human physical capability is influenced by many environmental and genetic factors, and it is generally accepted that physical capability phenotypes are highly polygenic. However, the ways in which relevant polymorphisms combine to influence the physical capability of individuals and populations are unknown. Initially, the literature was searched to identify associations between 23 genetic polymorphisms and human endurance phenotypes. Next, typical genotype frequencies of those polymorphisms in the general population were obtained from suitable literature. Using probability calculations, we found only a 0.0005% chance of a single individual in the world having the ‘preferable’ form of all 23 polymorphisms. As the number of DNA variants shown to be associated with human endurance phenotypes continues to increase, the probability of any single individual possessing the ‘preferable’ form of each polymorphism will become even lower. However, with population turnover, the chance of such genetically gifted individuals existing increases. To examine the polygenic endurance potential of a human population, a ‘total genotype score’ (for the 23 polymorphisms) was calculated for each individual within a hypothetical population of 1000 000. There was considerable homogeneity in terms of genetic predisposition to high endurance potential, with 99% of people differing by no more than seven genotypes from the typical profile. Consequently, with population turnover world and Olympic records should improve even without further enhancement of environmental factors, as more ‘advantageous’ polygenic profiles occasionally, though rarely, emerge. More broadly, human potential appears limited by the similarity of polygenic profiles at both the ‘elite sport’ and ‘chronic disorder’ ends of the performance continuum.

Measures of exercise intensity during soccer training drills with professional soccer players.

Recent evidence supports the use of certain soccer drills for combined technical and physical training. Therefore, it is important to be able to accurately monitor training intensity during soccer drills intended for physical development to allow the optimization of training parameters. Twenty-eight professional soccer players were assessed for heart rate (HR) and rating of perceived exertion (RPE) responses to 5 commonly used soccer training drills (2v2 to 8v8 drills). The responses of both HR and RPE differed significantly (p < 0.05) between the drills, generally showing an elevated response to drills involving lower player numbers. However, the 2v2 drill showed a significantly (p < 0.05) lower HR response (mean ± SD: 88.7 ± 1.2% HRmax) than 3v3 (91.2 ± 1.3% HRmax) and 4v4 drills (90.2 ± 1.6% HRmax). There was no significant correlation between the HR and RPE responses to the various drills (r = 0.60, p < 0.200). This poor relationship is probably because during the 2v2 drill, RPE was higher than during any of the other 6 drills, whereas HR was only fourth highest of the 6 drills. This demonstrates that HR and RPE are only poorly related during the intense drills used in this study, and that HR underestimates the intensity of the 2v2 drill. Heart rate demonstrated lower intersubject variability (1.3–2.2%) than RPE (5.1–9.9%). However, unlike HR, Borg 15-point RPE appears to be a valid marker of exercise intensity over a wide range of soccer training drills by maintaining validity in all drills and demonstrating acceptable intersubject variability. A combination of both HR- and RPE-based training load calculations appears optimal for use in soccer training.

Physiology: The ACE gene and muscle performance

Angiotensin-converting enzyme in human skeletal muscle can be encoded by either of two variants of the ACE gene, one of which carries an insertion of 287 base pairs. This longer allele gives rise to lower enzyme activity, and is associated with enhanced endurance performance and an anabolic response to intense exercise training. Here we examine training-related changes in the mechanical efficiency of human skeletal muscle (energy used per unit power output) and find that the presence of this ACE allele confers an enhanced mechanical efficiency in trained muscle.

SUITABILITY OF SOCCER TRAINING DRILLS FOR ENDURANCE TRAINING

Recent evidence suggests that certain soccer drills produce exercise intensities suitable for physical conditioning. However, it remains debatable whether soccer drills can provide a sufficiently unified exercise intensity among different players and on repetition of a drill, because movement patterns cannot be externally controlled during soccer drills. Good reliability and low variability of exercise intensity would enable all players to receive an appropriate training stimulus. The purpose of this study was to investigate intersubject variability and intrasubject reliability in exercise intensity during soccer drills. It was hypothesized that soccer drills that involve the highest exercise intensities would demonstrate the lowest intersubject variability and the highest intrasubject reliability. Heart rates of 23 professional soccer players were recorded during a range of soccer training drills. The drills consisted of 2 vs. 2 to 8 vs. 8 normal scoring games and 2 further possession games. Heart rate responses were examined for variability, reliability, and suitability for soccer endurance training. Coefficients of variation across players were less than 3% for all drills. Paired t-tests showed no significant differences in heart rate on repetition of the drills and 95% ratio limits of agreement were 1.8–3.8%. There were no significant correlations between exercise intensity and the statistical measures of variability and reliability. Several drills produced exercise intensities suitable for soccer endurance training with mean heart rate responses ranging from 87–91% HRmax. Soccer drills such as those used in the present study appear to be an adequate substitute for physical training without the ball and thus provide simultaneous skill and fitness training. The increase in training time spent developing technical ability and/or a reduction in total training time required may be useful for soccer teams.

The dependence of preferred competitive racing distance on muscle fibre type composition and ACTN3 genotype in speed skaters

It is generally accepted that muscle fibre composition may influence physical performance. The α‐actinin‐3 (ACTN3) gene R577X polymorphism is suspected to be one of the contributing gene variations in the determination of muscle fibre type composition and athletic status. In the present study, we examined the dependence of average preferred racing distance (PRD) on muscle fibre type composition of the vastus lateralis muscle in 34 subelite Russian speed skaters (20 men and 14 women) who competed in races of different length (500–10,000 m). We also investigated the association between the ACTN3 polymorphism and muscle fibre characteristics in 94 subjects (60 physically active healthy men and 34 speed skaters), as well as the relationship between PRD and ACTN3 genotype in 115 subelite and elite speed skaters. In addition, ACTN3 genotype and allele frequencies of the 115 speed skaters were compared with 1301 control subjects. The ACTN3 XX genotype frequency was significantly lower in sprinters (n = 39) compared with control subjects (2.6 versus 14.5%; P = 0.034). We observed a positive relationship between PRD and the proportion of slow‐twitch muscle fibres that was close to linear, but better fitted a logarithmic curve (r = 0.593, P < 0.0005). The ACTN3 R577X polymorphism was associated with muscle fibre composition (slow‐twitch fibres: RR genotype, 51.7 (12.8)%; RX, 57.4 (13.2)%; XX 61.5 (16.3)%; ρ= 0.215; P = 0.049) in the overall muscle biopsy group, and with PRD of all athletes (ρ= 0.24, P = 0.010), indicating that ACTN3 XX genotype carriers exhibit a higher proportion of slow‐twitch fibres and prefer to skate long‐distance races. However, the majority of the association between muscle fibre type and PRD was independent of ACTN3 genotype. In conclusion, the ACTN3 R577X polymorphism is associated with preferred racing distance in speed skaters and muscle fibre type composition. Thus, it is probably partly via associations with fibre type that the R577X polymorphism contributes to a small but perhaps important component of the ability to perform at a high level in speed skating.

Effects of basic training on material handling ability and physical fitness of British Army recruits.

No study has yet evaluated the efficacy of British Army basic training in improving material handling performance. Therefore, the purpose of this study was to evaluate the efficacy of the current British Army basic training in improving material handling performance and physical fitness. Forty-seven males (19.4 (3.2) years of age, 1753 (59) mm in height, 71.0 (9.6) kg in weight) and 10 females (21.5 (3.5) years, 1623 (45) mm, 62.5 (5.2) kg) served as subjects. Testing was carried out in the week prior to, and in the final week of, an 11-week basic training course. Maximal box lifts to two different heights, and repetitive lifting and carrying of a 10 kg load did not improve with training. Static (38 cm upright pull) and dynamic (incremental dynamic lift to 145 cm) lifting strength data concurred with the maximal box lift data in that no improvement was observed. Repetitive lifting and carrying of a 22 kg load improved (29.5%, p < 0.001), as did 3.2 km loaded march performance with 25 kg (15.7%, p < 0.001), but march performance with a 15 kg load did not. Predicted VO2max improved from 48.4 to 51.4 ml.kg-1.min-1, a change of 6.1% (p < 0.05). Fat-free mass increased by 0.9 kg (1.5%, p < 0.01), and body fat reduced by 2.7% of body mass (20.1%, p < 0.001), resulting in a loss of 1.2 kg of body mass (1.7%, p < 0.01). It is concluded that basic training in the British Army produces some favourable adaptations in recruits, especially in terms of aerobic fitness. However, the poor development of strength and material handling ability during training fails to improve the ability of soldiers to perform simulated military tasks, and it does little to reduce future injury risk while performing these tasks.