This series of reviews focuses on the most important neuromuscular function in many sport performances: the ability to generate maximal muscular power. Part 1, published in an earlier issue of Sports Medicine, focused on the factors that affect maximal power production while part 2 explores the practical application of these findings by reviewing the scientific literature relevant to the development of training programmes that most effectively enhance maximal power production. The ability to generate maximal power during complex motor skills is of paramount importance to successful athletic performance across many sports. A crucial issue faced by scientists and coaches is the development of effective and efficient training programmes that improve maximal power production in dynamic, multi-joint movements. Such training is referred to as ‘power training’ for the purposes of this review. Although further research is required in order to gain a deeper understanding of the optimal training techniques for maximizing power in complex, sportsspecific movements and the precise mechanisms underlying adaptation, several key conclusions can be drawn from this review. First, a fundamental relationship exists between strength and power, which dictates that an individual cannot possess a high level of power without first being relatively strong. Thus, enhancing and maintaining maximal strength is essential when considering the long-term development of power. Second, consideration of movement pattern, load and velocity specificity is essential when designing power training programmes. Ballistic, plyometric and weightlifting exercises can be used effectively as primary exercises within a power training programme that enhances maximal power. The loads applied to these exercises will depend on the specific requirements of each particular sport and the type of movement being trained. The use of ballistic exercises with loads ranging from 0% to 50% of one-repetition maximum (1RM) and/or weightlifting exercises performed with loads ranging from 50% to 90% of 1RM appears to be the most potent loading stimulus for improving maximal power in complex movements. Furthermore, plyometric exercises should involve stretch rates as well as stretch loads that are similar to those encountered in each specific sport and involve little to no external resistance. These loading conditions allow for superior transfer to performance because they require similar movement velocities to those typically encountered in sport. Third, it is vital to consider the individual athlete’s window of adaptation (i.e. the magnitude of potential for improvement) for each neuromuscular factor contributing to maximal power production when developing an effective and efficient power training programme. A training programme that focuses on the least developed factor contributing to maximal power will prompt the greatest neuromuscular adaptations and therefore result in superior performance improvements for that individual. Finally, a key consideration for the long-term development of an athlete’s maximal power production capacity is the need for an integration of numerous power training techniques. This integration allows for variation within power meso-/micro-cycles while still maintaining specificity, which is theorized to lead to the greatest long-term improvement in maximal power.

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Developing maximal neuromuscular power: part 2 - training considerations for improving maximal power production.

The aim of this systematic review was to determine if eccentric exercise is superior to concentric exercise in stimulating gains in muscle strength and mass. Meta-analyses were performed for comparisons between eccentric and concentric training as means to improve muscle strength and mass. In order to determine the importance of different parameters of training, subgroup analyses of intensity of exercise, velocity of movement and mode of contraction were also performed. Twenty randomised controlled trials studies met the inclusion criteria. Meta-analyses showed that when eccentric exercise was performed at higher intensities compared with concentric training, total strength and eccentric strength increased more significantly. However, compared with concentric training, strength gains after eccentric training appeared more specific in terms of velocity and mode of contraction. Eccentric training performed at high intensities was shown to be more effective in promoting increases in muscle mass measured as muscle girth. In addition, eccentric training also showed a trend towards increased muscle cross-sectional area measured with magnetic resonance imaging or computerised tomography. Subgroup analyses suggest that the superiority of eccentric training to increase muscle strength and mass appears to be related to the higher loads developed during eccentric contractions. The specialised neural pattern of eccentric actions possibly explains the high specificity of strength gains after eccentric training. Further research is required to investigate the underlying mechanisms of this specificity and its functional significance in terms of transferability of strength gains to more complex human movements.

https://bjsm.bmj.com/content/bjsports/43/8/556.full.pdf

The effects of eccentric versus concentric resistance training on muscle strength and mass in healthy adults: a systematic review with meta-analysis

Studies using animal models have been unable to determine the mechanical stimuli that most influence muscle architectural adaptation. We examined the influence of contraction mode on muscle architectural change in humans, while also describing the time course of its adaptation through training and detraining. Twenty-one men and women performed slow-speed (30 degrees /s) concentric-only (Con) or eccentric-only (Ecc) isokinetic knee extensor training for 10 wk before completing a 3-mo detraining period. Fascicle length of the vastus lateralis (VL), measured by ultrasonography, increased similarly in both groups after 5 wk (Delta(Con) = +6.3 +/- 3.0%, Delta(Ecc) = +3.1 +/- 1.6%, mean = +4.7 +/- 1.7%; P < 0.05). No further increase was found at 10 wk, although a small increase (mean approximately 2.5%; not significant) was evident after detraining. Fascicle angle increased in both groups at 5 wk (Delta(Con) = +11.1 +/- 4.0%, Delta(Ecc) = +11.9 +/- 5.4%, mean = 11.5 +/- 3.2%; P < 0.05) and 10 wk (Delta(Con) = +13.3 +/- 3.0%, Delta(Ecc) = +21.4 +/- 6.9%, mean = 17.9 +/- 3.7%; P < 0.01) in VL only and remained above baseline after detraining (mean = 13.2%); smaller changes in vastus medialis did not reach significance. The similar increase in fascicle length observed between the training groups mitigates against contraction mode being the predominant stimulus. Our data are also strongly indicative of 1) a close association between VL fascicle length and shifts in the torque-angle relationship through training and detraining and 2) changes in fascicle angle being driven by space constraints in the hypertrophying muscle. Thus muscle architectural adaptations occur rapidly in response to resistance training but are strongly influenced by factors other than contraction mode.

Influence of concentric and eccentric resistance training on architectural adaptation in human quadriceps muscles

This series of reviews focuses on the most important neuromuscular function in many sport performances, the ability to generate maximal muscular power. Part 1 focuses on the factors that affect maximal power production, while part 2, which will follow in a forthcoming edition of Sports Medicine, explores the practical application of these findings by reviewing the scientific literature relevant to the development of training programmes that most effectively enhance maximal power production. The ability of the neuromuscular system to generate maximal power is affected by a range of interrelated factors. Maximal muscular power is defined and limited by the force-velocity relationship and affected by the length-tension relationship. The ability to generate maximal power is influenced by the type of muscle action involved and, in particular, the time available to develop force, storage and utilization of elastic energy, interactions of contractile and elastic elements, potentiation of contractile and elastic filaments as well as stretch reflexes. Furthermore, maximal power production is influenced by morphological factors including fibre type contribution to whole muscle area, muscle architectural features and tendon properties as well as neural factors including motor unit recruitment, firing frequency, synchronization and intermuscular coordination. In addition, acute changes in the muscle environment (i.e. alterations resulting from fatigue, changes in hormone milieu and muscle temperature) impact the ability to generate maximal power. Resistance training has been shown to impact each of these neuromuscular factors in quite specific ways. Therefore, an understanding of the biological basis of maximal power production is essential for developing training programmes that effectively enhance maximal power production in the human.

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Developing maximal neuromuscular power: Part 1--biological basis of maximal power production.

Objective: To review the effect of calcitonin on bone density and fractures in postmenopausal women. Data Source: We searched MEDLINE and EMBASE from 1966 to 2000 and examined citations of relevant articles and the proceedings of international osteoporosis meetings. We contacted osteoporosis investigators to identify additional studies and primary authors for unpublished data. Study Selection: We included 30 studies that randomized women to calcitonin or an alternative (placebo or calcium and/or vitamin D) and measured bone density or fracture incidence for at least 1 yr. Data Extraction: For each trial, three independent reviewers assessed the methodological quality and abstracted data. Data Synthesis: Calcitonin reduced the incidence of vertebral fractures, with a pooled relative risk (RR) of 0.46 [95% confidence interval (CI) 0.25-0.87, P = 0.02, n = 1404, 4 trials]. However, the RR from the one relatively large randomized controlled trial (RCT) was 0.79 (95% CI 0.62-1.00, P = 0.05, n = 1108). For nonvertebral fractures, the pooled RR was 0.52 (95% CI 0.22-1.23, P = 0.14, n = 1481, 3 trials). Once again, the single large trial showed a less impressive effect than the smaller trials (RR 0.80, 95% CI 0.59-1.09, P = 0.16, n = 1245). For bone density of the lumbar spine, the pooled weekly dose of 250 to 2800 IU per week resulted in significant increase in the weighted mean difference (WMD) of 3.74 (2.04-5.43, P < 0.01, n = 2260, 24 trials). The combined forearm showed a similar effect, with a WMD of 3.02 (95% CI 0.98-5.07, P < 0.01, n = 468, 9 trials). At the femoral neck, the pooled weighted mean difference showed a nonsignificant trend toward benefit, WMD 3.80 (95% CI-0.32-7.91, P = 0.07, 9 trials, n = 513). Methodologically weaker studies tended to show greater effects on bone density, and the lumbar spine results suggested the possibility of publication bias. Conclusions: Calcitonin likely increases bone density in postmenopausal women predominantly at the lumbar spine and forearm for weekly doses of greater than 250 IU, although the true effect may be smaller than the pooled estimate would suggest. Calcitonin likely reduces the risk of vertebral fracture; its effect on nonvertebral fracture remains uncertain.

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VI. Meta-Analysis of Calcitonin for the Treatment of Postmenopausal Osteoporosis

The aims of this study were to assess changes in muscle architecture, isometric and dynamic strength of the leg extensor muscles, resulting from dynamic resistance training, and the relationships between strength and muscle architecture variables. The participants (n = 30) were randomly assigned to one of two groups. The training group (n = 16; age 21.8 +/- 2.3 years, body mass 74.8 +/- 9.2 kg, height 1.75 +/- 0.08 m) performed dynamic resistance training for 13 weeks. The control group (n = 14; age 19.9 +/- 1.5 years, body mass 74.0 +/- 8.5 kg, height 1.76 +/- 0.05 m) did not perform any resistance training. Maximal dynamic and isometric strength were tested in both groups, before and after the training period. The members of the training group used the free-weight squat lift (90 degrees ) as their training exercise. The concentric phase of the squat was performed explosively. Skeletal muscle architecture of the vastus lateralis was visualized using ultrasonography. At the end of the study, significant increases in vastus lateralis muscle thickness (+6.9%, P < 0.001), fascicle length (+10.3%, P < 0.05), one-repetition maximum (+8.2%, P < 0.05), rate of force development (+23.8%, P < 0.05) and average force produced in the first 500 ms (+11.7%, P < 0.05) were seen only in the training group. Adaptations to the muscle architecture in the training group limited the loss of fibre force, and improved the capacity for developing higher velocities of contraction. The architectural changes in the training group were similar to those seen in studies where high-speed training was performed. In conclusion, dynamic resistance training with light loads leads to increases in muscle thickness and fascicle length, which might be related to a more efficient transmission of fibre force to the tendon.

Effects of dynamic resistance training on fascicle length and isometric strength.

Predictors of chronic ankle instability: Analysis of peroneal reaction time, dynamic balance and isokinetic strength.

Background Tendinopathy is an overuse tendon injury that occurs in loaded tendons and results in pain and functional impairment. Although many treatments for painful tendons are described, the scientific evidence for most of the conservative and surgical treatments is not always conclusive. Objectives This study was designed to evaluate the efficacy of 3 different interventions in patients with Achilles tendinopathy. The interventions include the combination of 2 physical therapy programs (eccentric training [EC] or passive stretching [PS]) with a supplement containing mucopolisaccharides. The efficacy of the interventions was evaluated depending on the stage of the disease. Methods Fifty-nine patients were randomly assigned to 1 of 3 treatment groups, and classified according to the disease stage: reactive versus degenerative tendinopathy. Treatment groups were EC; EC + a dietary supplement containing mucopolisaccharides, type I collagen, and vitamin C (MCVC); and a passive stretching program + MCVC. Patients were evaluated at baseline, 6 weeks, and 12 weeks with the Victorian Institute of Sports Assessment-Achilles questionnaire for function, a visual analog scale for pain, and ultrasound characterization for the evolution of tendon structure. Results A significant improvement in Victorian Institute of Sports Assessment-Achilles questionnaire score, pain at rest, and pain during activity were detected in all 3 treatment groups at 6 and 12 weeks' follow-up when compared with baseline. In patients with reactive tendinopathy, the reduction in pain at rest was greater in the groups who took the supplemental MCVC than in the EC alone group ( P Conclusions MCVC seems to be therapeutically useful for management of tendinopathies, providing some additional benefit to physical therapy. This is especially evident in early stages of the disease, when the tendon does not present severe matrix and vascular changes. ClinicalTrials.gov identifier NCT01691716.

A 3-Arm Randomized Trial for Achilles Tendinopathy: Eccentric Training, Eccentric Training Plus a Dietary Supplement Containing Mucopolysaccharides, or Passive Stretching Plus a Dietary Supplement Containing Mucopolysaccharides

Background 
The continued practice of a sport linked to the unilateral predominance of the dominant side can provoke chronic asymmetric adaptations in the myotendinous structure and mechanical properties. Objectives: The main purpose was to determine whether asymmetry between the preferred and non-preferred lower limb is present in the lower limb tendon structure, muscle architecture and stiffness values of professional badminton players.


Methods 
Sixteen male professional badminton players (age = 24.1 ± 6.7 years; body height = 177.90 ± 7.53 cm) participated in this study. The muscle architecture of the vastus lateralis (VL), medial gastrocnemius (MG) and lateral gastrocnemius (LG) and the structure of patellar and Achilles tendons were measured in the dominant and non-dominant lower limb with ultrasonography. Stiffness was also measured at the same points with a hand-held MyotonPro. Significant differences between the dominant and non-dominant lower limb were determined using Student’s t test for related samples.


Results 
Bilateral differences were observed for thickness, width and cross-sectional area (CSA) in both tendons showing higher values for the dominant side: patellar tendon CSA (2.02 ± 0.64 vs. 1.51 ± 0.42 cm2; p < 0.05) and Achilles tendon CSA (1.12 ± 0.18 vs. 0.92 ± 0.28 cm2; p < 0.05). No significant differences were observed in muscle architecture and myotonic variables between the dominant and non-dominant lower limb.


Conclusions 
The prolonged practice of badminton caused asymmetries in the CSA, width and thickness of the patellar and Achilles tendon between the dominant and non-dominant lower limbs. No bilateral differences were found in the muscle architecture of VL, MG and LG or in the stiffness of any muscle or tendon analyzed.

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Myotendinous asymmetries derived from the prolonged practice of badminton in professional players

Background: The ligament sprain of the lateral ankle is the most frequent injury that occurs when participating in sports. Whole body vibration (WBV) is a training method that has been recently introduced as a rehabilitative tool for treatment of athletes. It has been hypothesized that the transmission of mechanical oscillations from the vibrating platform may lead to physiological changes in muscle spindles, joint mechanoreceptors, as well as improve balance. Propose: The aim of this study was to assess the effects of a 6-week WBV training program on the reflex response mechanism of the peroneus longus (PL), peroneus brevis (PB) and anterior tibialis (AT) muscles in ankle inversion at 30o from horizontal, in a static position. Methods: This study was a single-blinded and randomized controlled trial. Forty-four healthy, physically active participants were randomly split into two groups: the experimental group (n = 26) (the WBV training) and control group (n = 18). Reaction time (RT), maximum electromyographic (EMG) peak (peak EMG), time to the maximum peak EMG (peak EMG time) and reflex electrical activity of all the muscles were assessed before and after the WBV training through surface EMG. Results: After 6-weeks WBV training, there were no significant changes in the variables analysed for all the muscles involved. Conclusion: A 6-week WBV training does not improve the reflex response mechanism of the lateral stabilizing muscles of the ankle.

Fernando Jiménez

Papers

Effects of dynamic resistance training on fascicle length and isometric strength.

Predictors of chronic ankle instability: Analysis of peroneal reaction time, dynamic balance and isokinetic strength.

A 3-Arm Randomized Trial for Achilles Tendinopathy: Eccentric Training, Eccentric Training Plus a Dietary Supplement Containing Mucopolysaccharides, or Passive Stretching Plus a Dietary Supplement Containing Mucopolysaccharides

Myotendinous asymmetries derived from the prolonged practice of badminton in professional players

Effects of 6‐week whole body vibration training on the reflex response of the ankle muscles: a randomized controlled trial