Abstract
It is well-documented that strength training (ST) improves measures of muscle strength in young athletes. Less is known on transfer effects of ST on proxies of muscle power and the underlying dose-response relationships. The objectives of this meta-analysis were to quantify the effects of ST on lower limb muscle power in young athletes and to provide dose-response relationships for ST modalities such as frequency, intensity, and volume. A systematic literature search of electronic databases identified 895 records. Studies were eligible for inclusion if (i) healthy trained children (girls aged 6–11 y, boys aged 6–13 y) or adolescents (girls aged 12–18 y, boys aged 14–18 y) were examined, (ii) ST was compared with an active control, and (iii) at least one proxy of muscle power [squat jump (SJ) and countermovement jump height (CMJ)] was reported. Weighted mean standardized mean differences (SMDwm) between subjects were calculated. Based on the findings from 15 statistically aggregated studies, ST produced significant but small effects on CMJ height (SMDwm = 0.65; 95% CI 0.34–0.96) and moderate effects on SJ height (SMDwm = 0.80; 95% CI 0.23–1.37). The sub-analyses revealed that the moderating variable expertise level (CMJ height: p = 0.06; SJ height: N/A) did not significantly influence ST-related effects on proxies of muscle power. “Age” and “sex” moderated ST effects on SJ (p = 0.005) and CMJ height (p = 0.03), respectively. With regard to the dose-response relationships, findings from the meta-regression showed that none of the included training modalities predicted ST effects on CMJ height. For SJ height, the meta-regression indicated that the training modality “training duration” significantly predicted the observed gains (p = 0.02), with longer training durations (>8 weeks) showing larger improvements. This meta-analysis clearly proved the general effectiveness of ST on lower-limb muscle power in young athletes, irrespective of the moderating variables. Dose-response analyses revealed that longer training durations (>8 weeks) are more effective to improve SJ height. No such training modalities were found for CMJ height. Thus, there appear to be other training modalities besides the ones that were included in our analyses that may have an effect on SJ and particularly CMJ height. ST monitoring through rating of perceived exertion, movement velocity or force-velocity profile could be promising monitoring tools for lower-limb muscle power development in young athletes.
Highlights
Coaches’ and fitness professionals’ daily task is to enhance performance of their athletes using effective and efficient training regimes
After a careful review of the full texts, 23 articles were excluded and the remaining 15 articles were included in this meta-analysis
Our analyses revealed small strength training (ST)-related effects (SMDwm = 0.65; 95% confidence intervals (95% CI) 0.34– 0.96) for countermovement jump (CMJ) height, with moderate heterogeneity (I2 = 53.11%) (Figures 2, 3)
Summary
Coaches’ and fitness professionals’ daily task is to enhance performance of their athletes using effective and efficient training regimes. High levels of muscle power represent important performance determinants in several sports (e.g., athletics, combat sports, rugby) and are related to success in sport competition (James et al, 2016; Slimani and Nikolaidis, 2017). Granacher et al (2016) postulated that muscle power should be systematically developed during daily strength and conditioning routines in athletes. Athletes’ performance in muscle power can be estimated using different tests. Vertical jump tests represent easy-to-administer, frequently used, and reliable tests for the assessment of muscle power. Markovic et al (2004) reported that the countermovement jump (CMJ) and squat jump (SJ) tests are well-suited since they afford complex motor coordination between upper- and lower-body segments and because performance-related measures like jump height are highly associated with power measures (Kons et al, 2018) Vertical jump tests represent easy-to-administer, frequently used, and reliable tests for the assessment of muscle power. Markovic et al (2004) reported that the countermovement jump (CMJ) and squat jump (SJ) tests are well-suited since they afford complex motor coordination between upper- and lower-body segments and because performance-related measures like jump height are highly associated with power measures (Kons et al, 2018)
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