BASES Position Statement on Guidelines for Resistance Exercise in Young People

Data Informing Governing Body Resistance-Training Guidelines Exhibit Sex Bias: An Audit-Based Review

The objective of this review was to examine the ratio of female and male participants utilised in data informing consensus statements and position stands in the field of resistance training (RT). In order to achieve this objective, we conducted an 'audit' style review. We accessed three databases: SPORTDiscus, MEDLINE and Google Scholar utilising the following search terms: resistance or strength training AND consensus statements or position statements/stands. Eligibility criteria included consensus statements and position stands for RT in youth, adults and older adults. In this paper we have used the term 'female' to describe biological sex. Gender is a social construct and often describes roles and behaviours that society assigns to men or women. In this paper we have used the term 'women' to describe gender. Reference lists from each guideline were screened with the number of male and female participants extracted from each study. We also extracted data on the gender of the authors of the statements. We located 11 guidelines encompassing a total of 104,251,363 participants. Youth guidelines were comprised of 69% male participants. There were 287 studies that included both sexes, 205 male-only and 92 female-only studies. Adult guidelines were comprised of 70% male participants. There were 104 studies that included both sexes, 240 male-only and 44 female-only studies. Older adult guidelines were comprised of 54% female participants. There were 395 studies that included both sexes, 112 male-only and 83 female-only studies. Women authors comprised 13% of all authors of position stands and consensus statements. These results demonstrate an under-representation of females and women as both participants and as authors. It is imperative to ensure that data informing governing body guidelines and consensus statements are representative of the population they aim to inform. If this is not possible, guidelines should clearly state when their data and recommendations are based primarily upon one sex.

Efficacy of school-based interventions for improving muscular fitness outcomes in children: A systematic review and meta-analysis

The World Health Organization recommends that children should engage in an average of 60 min of moderate-to-vigorous physical activity (MVPA) per day and should perform activities that strengthen muscle and bone at least 3 days a week. Public health professionals as well as pediatric researchers have identified schools as a strategic place to promote muscular strength development. Thus, the aim of this systematic review and meta-analysis was to investigate the efficacy of school-based exercise interventions for improving muscular fitness (MF) in children. Searches were conducted in three databases. Eligible criteria were randomized and non-randomized controlled trials evaluating the effects of school-based exercise interventions on MF (i.e. muscular strength, muscular power, and local muscular endurance) in children under 13 years of age. Risk of bias by the National Institutes of Health tool was appraised, and pooled effect sizes (Hedges'g) were calculated using random-effects inverse-variance analyses. Seventeen studies enrolling 1653 children (28% girls were analyzed). Exercise interventions, mostly combined interventions targeting selected domains of MF, were associated with significant moderate increases in local muscular endurance (g = 0.65 95% CI, 0.13 to 1.17, p = 0.020; I²= 85.0%) and muscular strength and muscular power (g = 0.33 95% CI, 0.16 to 0.51, p = 0.001; I²= 59.3%), with higher effects using interventions with ≥3 sessions per week. Our findings indicate that school-based exercise that includes strength building exercises may improve MF in children and, consequently, prepare modern day youth for the demands of exercise and sport activities. HighlightsSchool-based muscle and bone strengthening exercises performed at least 3 days per week may serve to support the development of muscular fitness in girls and boysIntegrative interventions that include a variety of strength and conditioning activities seem to be a promising strategy to promote muscular fitness in school environmentFuture research should standardize assessment methods for use with children in the school context and should include interventions with girlsIt is of interest to a growing number of health care providers, fitness professionals and physical education teachers to encourage participation in well-designed muscle and bone strengthening exercises.

Regulatory Mechanisms of Muscle Mass: The Critical Role of Resistance Training in Children and Adolescent

Muscle mass and strength are subjected to several regulations. We found endocrine signals such as growth hormone, insulin-like growth factor 1, testosterone, thyroid hormones, and glucocorticoids among them. Neural inputs also influence muscle development, modulating mass and strength. Among the external stimuli that modulate these muscular features is physical training such as resistance and endurance training. Specifically, resistance training can mediate an increase in muscle mass by hypertrophy in adults, but the effects in children and adolescents are full of myths for most of the population. However, the evidence shows that the impact of resistance training on children and adolescents is clear and provides a wide range of benefits. However, qualified professionals must be available since exercise prescription and subsequent supervision must follow this population's abilities, needs, and interests.

Weightlifting for Children and Adolescents: A Narrative Review

The involvement of youth in the sport of weightlifting and the use of weightlifting methods as part of training for youth sport performance appears to be increasing. Weightlifting for children and adolescents has been criticized in some circles and is a controversial aspect of resistance training for young people. Although injuries can occur during weightlifting and related activities, the incidence and rate of injury appear to be relatively low and severe injury is uncommon. A number of performance, physical, and physiological variables, such as body composition, strength, and power, are improved by weightlifting training in children, adolescents, and young athletes. Manipulating program variables, when appropriate, can have a substantial and profound influence on the psychological, physiological, physical, and performance aspects of weightlifters. An understanding of the sport, scientific training principles, and musculoskeletal growth development is necessary to properly construct a reasonable and appropriate training program. A scientific background aids in providing an evidenced basis and sound rationale in selecting appropriate methods and directing adaptations toward more specific goals and enables the coach to make choices about training and competition that might not otherwise be possible. If weightlifting training and competition are age group appropriate and are properly supervised, the sport can be substantially safe and efficacious.

Efficacy of School-Based Interventions for Improving Muscular Fitness Outcomes in Adolescent Boys: A Systematic Review and Meta-analysis

BACKGROUND

It has been reported that boys' and girls' physical activity (PA) levels decline throughout adolescence. Boys are at risk of physical inactivity during adolescence; however, in intervention research, they are an under-represented group relative to girls. It is suggested that the school environment may be central to developing interventions that support adolescents in meeting the current PA guidelines. The aim of this systematic review and meta-analysis was to investigate the efficacy of school-based physical activity interventions for improving muscular fitness (MF) in adolescent males.

METHODS

This systematic review and meta-analysis followed the preferred reporting systems for meta-analyses guidelines and was registered on PROSPERO (Registration number: CRD42018091023). Eligible studies were published in English within peer-reviewed articles. Searches were conducted in three databases, with an additional grey literature search in Google Scholar. Studies investigating MF outcomes were included.

RESULTS

There were 43 data sets identified across 11 studies, from seven countries. Overall methodological quality of the studies was moderate-to-strong. Interventions targeting MF evidenced a small-to-medium effect (g = 0.32, CI 0.17, 0.48, p < 0.00). Subgroup analyses of MF delivery method resulted in small-to-medium effects: upper limb MF measures (g = 0.28, 95% CI - 0.02, 0.58, p = 0.07), lower limb MF measures (g = 0.28, 95% CI 0.09, 0.68, p = 0.03), combined MF activities (g = 0.24, 95% CI - 0.04 to 0.49, p = 0.05), plyometric activities (g = 0.39, 95% CI 0.09, 0.68, p = 0.01), body weight (g = 0.27, 95% CI - 0.10, 0.65, p = 0.15), and traditional MF methods (g = 0.43, 95% CI 0.09, 0.78, p = 0.01).

CONCLUSIONS

School-based interventions which aimed to increase MF outcomes in adolescent boys demonstrated small-to-moderate effects. Traditional and plyometric methods of resistance training appear to be the most effective form of PA delivery in adolescent males. More quality research is required to assess the impact of MF delivered in the school environment to inform future intervention design.

Maturity offset affects standing postural control in youth male soccer players

Quantifying the response of postural control in developmental athletes makes it possible to understand critical coordination and learning phases and to improve technical-physical interventions. However, the influence of maturation on postural control amongst young soccer players has neither been tested using quantitative methods, nor over a wide age range. In this study, we examined stabilometric parameters of 238 young male soccer players from 9 to 17 years old relative to maturity offset. Two 30-s tests (eyes open and eyes closed) were recorded on a baropodometric platform at 50 Hz. Participants were split into six groups according to their maturity offset, expressed as years from individual's peak height velocity. Dependent variables were: Sway Area, Center-of-Pressure velocity, standard deviation of the antero-posterior and medio-lateral Center-of-Pressure trajectory, Romberg Quotient. Sway Area was significantly higher in players with maturity offset <-1.5 than in groups with maturity offset > 0.5 years (p < 0.001, large effect). Center-of-Pressure velocity markedly dropped in players with maturity offset >-0.5 years (p < 0.001, very large effect). Antero-posterior standard deviation was higher before than after peak height velocity (p < 0.05, large effect) and significantly higher with closed eyes at some points. Medio-lateral standard deviation was higher in the youngest group of players (maturity offset <-2.5 years, large effect) than in those with maturity offset >-0.5 years. In sum, stabilometric parameters improved with age until zero maturity offset was achieved. Thereafter, variables describing postural control in developing soccer players were almost stable. No evidence of a changing role of vision in postural sway control during maturation was observed.

The Importance of Fundamental Motor Skills in Identifying Differences in Performance Levels of U10 Soccer Players

This study examined the differences in fundamental motor skills (FMSs) and specific conditioning capacities (SCCs) between a coach’s classification of first team (FT) and second team (ST) U10 soccer players and examined the most important qualities based on how the coach differentiates them. The FT (n = 12; M_age = 9.72 ± 0.41) and ST (n = 11; M_age = 9.57 ± 0.41) soccer players were assessed using the Test of Gross Motor Development-2, standing long jump, sit and reach, diverse sprints, and the 20 m multistage fitness test (MSFT). The coach’s subjective evaluation of players was obtained using a questionnaire. No significant differences existed between the FT and ST in any variables (p > 0.05). However, large and moderate effect sizes were present in favour of the FT group in locomotor skills (d = 0.82 (0.08, 1.51)), gross motor quotient (d = 0.73 (0.00, 1.41)), height (d = 0.61 (−0.12, 1.29)), MSFT (d = 0.58 (−0.14, 1.25)), and maximum oxygen uptake (VO_2max) (d = 0.55 (−0.17, 1.22)). Furthermore, the coach perceived the FT group as having greater technical and tactical qualities relative to ST players. This suggests that it might be more relevant for players of this age to develop good FMS connected to technical skills, before focusing on SCC. Therefore, it might be beneficial for soccer coaches to emphasize the development of FMSs due to their potential to identify talented young soccer players and because they underpin the technical soccer skills that are required for future soccer success.

The Effect of Resistance Training Interventions on 'The Self' in Youth: a Systematic Review and Meta-analysis

Background

There is growing evidence that physical activity (PA) is beneficial for the mental health of young people. One area that has been widely examined is the impact of PA on ‘the self’, which is a term that encompasses a range of specific and related terms (e.g. self-esteem, self-efficacy, self-perceptions). There is evidence that PA is strongly associated with ‘the self’ in childhood and beyond. However, the impact of the specific PA of resistance training (RT) is not yet clear. The purpose of this review was to advance knowledge on the potential of RT for enhancing mental health by examining the effect of RT interventions on ‘the self’ in youth.

Methods

This systematic review followed the PRISMA guidelines (PROSPERO registration number CRD42016038365). Electronic literature databases were searched from the year of their inception to October 2018. The search included English language articles that examined the effect of isolated RT on the broad term of ‘the self’ in youth, with participants of school age (5–18 years). Data were extracted using an electronic form by one reviewer with 10% conducted by a second reviewer. The ‘Quality Assessment Tool for Quantitative Studies’ was used to assess the quality and risk of bias and was conducted by two reviewers.

Results

From seven peer-reviewed studies, ten data sets were included exploring seven outcomes related to ‘the self’ in participants aged between 10 and 16 years. Four of these studies (including seven data sets) were combined in a meta-analysis, with results from the remaining three studies reported separately. Significant intervention effects were identified for resistance training self-efficacy (Hedges’ g = 0.538, 95% CI 0.254 to 0.822, P < 0.001), physical strength (Hedges’ g = 0.289, 95% CI 0.067 to 0.511, P = 0.011), physical self-worth (Hedges’ g = 0.319, 95% CI 0.114 to 0.523, P = 0.002) and global self-worth (Hedges’ g = 0.409, 95% 0.149 to 0.669, P = 0.002). Although not statistically significant, the effect sizes for the remaining three outcomes were body attractiveness (Hedges’ g = 0.211, 95% CI − 0.031 to 0.454, P = 0.087), physical condition (Hedges’ g = 0.089, 95% CI − 0.238 to 0.417, P = 0.593) and sport competence (Hedges’ g = 0.004, 95% CI − 0.218 to 0.225, P = 0.974). There was variable quality of studies, with just two studies being classified as ‘strong’.

Conclusion

This is the first review to synthesise research on the effects of isolated RT interventions on ‘the self’. The findings indicate that RT has a positive impact on some aspects of ‘the self’ in youth. More high-quality studies should be conducted to further investigate this topic. If validated, this type of intervention could have a positive impact on ‘the self’ and ultimately improve the health of individuals not only during childhood but as they progress through life.

The effect of resistance training interventions on fundamental movement skills in youth: a meta-analysis

BACKGROUND

Fundamental movement skills (FMS) are strongly related to physical activity (PA) in childhood and beyond. To develop FMS, resistance training (RT) may be a favourable intervention strategy. The purpose of this meta-analysis was to systematically examine the effect of RT interventions on FMS in youth.

METHODS

Meta-analysis followed the PRISMA guidelines (Prospero registration number CRD42016038365). Electronic literature databases were searched from the year of their inception up to and including June 2017. The search strategy aimed to return studies that included product and process-oriented measures as a means of assessing FMS. Studies from English language peer-reviewed published articles that examined the effect of RT on indicators of FMS in youth, with participants of school age (5-18 years) were included.

RESULTS

Thirty-three data sets were included exploring five outcomes related to FMS. Studies included only reported product-oriented outcomes. Significant intervention effects were identified for: sprint (Hedges' g = 0.292, 95% CI 0.017 to 0.567, P = 0.038), squat jump (Hedges' g = 0.730, 95% CI 0.374 to 1.085, P = < 0.001), standing long jump (Hedges' g = 0.298, 95% CI 0.096 to 0.499, P = 0.004), throw (Hedges' g = 0.405, 95% CI 0.094 to 0.717, P = 0.011) and vertical jump (Hedges' g = 0.407, 95% CI 0.251 to 0.564, P = < 0.001). There was variable quality of studies, with 33.3% being classified as 'strong'.

CONCLUSION

RT has a positive impact on indicators of FMS in youth but more high-quality studies should be conducted to further investigate the role RT may play in the development of FMS. Additionally, to more comprehensively evaluate the impact of RT on FMS, there is a need for FMS assessments that measure both process- and product-oriented outcomes.

The effect of resistance training interventions on weight status in youth: a meta-analysis

BACKGROUND

There has been a rise in research into obesity prevention and treatment programmes in youth, including the effectiveness of resistance-based exercise. The purpose of this meta-analysis was to examine the effect of resistance training interventions on weight status in youth.

METHODS

Meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines and was registered on PROSPERO (registration number CRD42016038365). Eligible studies were from English language peer-reviewed published articles. Searches were conducted in seven databases between May 2016 and June 2017. Studies were included that examined the effect of resistance training on weight status in youth, with participants of school age (5-18 years).

RESULTS

There were 24 complete sets of data from 18 controlled trials (CTs) which explored 8 outcomes related to weight status. Significant, small effect sizes were identified for body fat% (Hedges' g = 0.215, 95% CI 0.059 to 0.371, P = 0.007) and skinfolds (Hedges' g = 0.274, 95% CI 0.066 to 0.483, P = 0.01). Effect sizes were not significant for: body mass (Hedges' g = 0.043, 95% CI - 0.103 to 0.189, P = 0.564), body mass index (Hedges' g = 0.024, 95% CI - 0.205 to 0.253, P = 0.838), fat-free mass (Hedges' g = 0.073, 95% CI - 0.169 to 0.316, P = 0.554), fat mass (Hedges' g = 0.180, 95% CI - 0.090 to 0.451, P = 0.192), lean mass (Hedges' g = 0.089, 95% CI - 0.122 to 0.301, P = 0.408) or waist circumference (Hedges' g = 0.209, 95% CI - 0.075 to 0.494, P = 0.149).

CONCLUSIONS

The results of this meta-analysis suggest that an isolated resistance training intervention may have an effect on weight status in youth. Overall, more quality research should be undertaken to investigate the impact of resistance training in youth as it could have a role to play in the treatment and prevention of obesity.

Cortical activation pattern during shoulder simple versus vibration exercises: a functional near infrared spectroscopy study

To date, the cortical effect of exercise has not been fully elucidated. Using the functional near infrared spectroscopy, we attempted to compare the cortical effect between shoulder vibration exercise and shoulder simple exercise. Eight healthy subjects were recruited for this study. Two different exercise tasks (shoulder vibration exercise using the flexible pole and shoulder simple exercise) were performed using a block paradigm. We measured the values of oxygenated hemoglobin in the four regions of interest: the primary sensory-motor cortex (SM1 total, arm somatotopy, and leg and trunk somatotopy), the premotor cortex, the supplementary motor area, and the prefrontal cortex. During shoulder vibration exercise and shoulder simple exercise, cortical activation was observed in SM1 (total, arm somatotopy, and leg and trunk somatotopy), premotor cortex, supplementary motor area, and prefrontal cortex. Higher oxygenated hemoglobin values were also observed in the areas of arm somatotopy of SM1 compared with those of other regions of interest. However, no significant difference in the arm somatotopy of SM1 was observed between the two exercises. By contrast, in the leg and trunk somatotopy of SM1, shoulder vibration exercise led to a significantly higher oxy-hemoglobin value than shoulder simple exercise. These two exercises may result in cortical activation effects for the motor areas relevant to the shoulder exercise, especially in the arm somatotopy of SM1. However, shoulder vibration exercise has an additional cortical activation effect for the leg and trunk somatotopy of SM1.

State of the Art Reviews: Resistance Training for Children and Adolescents

Although much of what we understand about the stimulus of resistance exercise has been gained by exploring the responses of adults to various training protocols, research into the effects of resistance exercise on children and adolescents has increased over the past decade. Despite outdated concerns that resistance training was ineffective or unsafe for youth, research increasingly suggests that resistance training can be a safe and effective method of exercise for children and adolescents provided that appropriate training guidelines are followed. In addition to enhancing motor skills and sports performance, regular participation in a youth resistance training program has the potential to positively influence several measurable indices of health. It helps strengthen bone, facilitate weight control, enhance psychosocial well-being, and improve one's cardiovascular risk profile. Furthermore, a stronger musculoskeletal system will enable boys and girls to perform life's daily activities with more energy and vigor and may increase a young athlete's resistance to sports-related injuries. Along with other types of physical activity, a properly designed youth resistance training program can offer observable health value to children and adolescents when appropriately prescribed and supervised.

Resistance strength training exercise in children with spinal muscular atrophy

INTRODUCTION

Preliminary evidence in adults with spinal muscular atrophy (SMA) and in SMA animal models suggests exercise has potential benefits in improving or stabilizing muscle strength and motor function.

METHODS

We evaluated feasibility, safety, and effects on strength and motor function of a home-based, supervised progressive resistance strength training exercise program in children with SMA types II and III. Up to 14 bilateral proximal muscles were exercised 3 times weekly for 12 weeks.

RESULTS

Nine children with SMA, aged 10.4 ± 3.8 years, completed the resistance training exercise program. Ninety percent of visits occurred per protocol. Training sessions were pain-free (99.8%), and no study-related adverse events occurred. Trends in improved strength and motor function were observed.

CONCLUSIONS

A 12-week supervised, home-based, 3-day/week progressive resistance training exercise program is feasible, safe, and well tolerated in children with SMA. These findings can inform future studies of exercise in SMA.

The sit up test to exhaustion as a test for muscular endurance evaluation

AIMS/HYPOTHESIS

The aim of this study was to examine the sit up test to exhaustion as a field test for muscular endurance evaluation in a sample of sedentary people of both sexes.

METHODS

A cross-sectional study was performed. Three-hundred-eighty-one participants volunteered for the study (28.5 ± 10.0 years; 168.2 ± 8.9 cm; 65.1 ± 11.1 kg), of which 194 males (27.5 ± 10.2 years; 173.6 ± 7.0 cm; 71.2 ± 5.2 kg) and 187 females (29.6 ± 10.1 years; 162.6 ± 7.1 cm; 58.7 ± 8.9 kg). Each subject voluntarily and randomly performed: a sit up test (SUT), a push up test (PUT), and a free weight squat test (ST), all till exhaustion. A multiple regression analysis was adopted for data analysis. Subsequently a percentile model for muscle endurance was developed. The 25th, 50th, and 75th percentile were identified as upper limit for low muscular endurance, average muscular endurance, and lower limit for high muscular endurance, respectively.

RESULTS

Considering the sit up test as the dependent variable, the coefficients (R(2) = 0.23; r = 0.49; p < 0.001), and (R(2) = 0.31; r = 0.57; p < 0.001) emerged from a multiple regression analysis applied with respect to the push up test and the squat test, respectively. Gender stratification showed regression coefficients of (R(2) = 0.19; r = 0.44; p < 0.001) for SUT vs. PUT, and (R(2) = 0.30; r = 0.56; p < 0.001) for SUT vs. ST in male; and (R(2) = 0.23; r = 0.49; p < 0.001) for SUT vs. PUT, and (R(2) = 0.34; r = 0.59; p < 0.001) for SUT vs. ST in female.

CONCLUSIONS/INTERPRETATION

The SUT showed low inter-relation with the other proposed tests indicating that the adoption of a single test for the global evaluation of muscle endurance is not the optimal approach. Moreover, the SUT was found to be inexpensive, safe, and appropriate for core muscle endurance measurement for both male and female.

Peripheral quantitative computed tomography (pQCT) reveals low bone mineral density in adolescents with motor difficulties

This is the first reported study to describe local bone mineral density, assess parameters of fracture risk and report history of fractures in adolescents with motor difficulties. Motor difficulties evidenced by poor coordination in adolescence should be considered a new risk factor for below-average bone strength and structure and fracture risk.

INTRODUCTION

Adolescents with motor difficulties are characterised by poor coordination and low levels of physical activity and fitness. It is possible these deficits translate into below-average bone strength and structure. The objectives of this study were to describe local bone mineral density (BMD), assess parameters of fracture risk (stress-strain index, SSI) and report history of fractures in this group.

METHODS

Thirty-three adolescents (13 females), mean age of 14.3 (SD = 1.5) years, with motor difficulties underwent peripheral quantitative computed tomography (pQCT) measurements at proximal (66 %) and distal (4 %) sites of the non-dominant radius (R4 and R66) and tibia (T4 and T66). One sample t test was used to compare Z-scores for total BMD, trabecular density, cortical density and stress strain index (SSI) against standardized norms.

RESULTS

Significant differences were present at R4 total density mean Z-score = -0.85 (SD = 0.7, p < 0.001), R66 cortical density mean Z-score = -0.74 (SD = 1.97, p = 0.038), R66 SSI mean Z-score = -1.00 (SD = 1.08, p < 0.001) and T66 SSI mean Z-score = -0.70 (SD = 1.15, p < 0.001). There was a higher incidence of fractures (26.9 %) compared to the normal population (3-9 %).

CONCLUSIONS

Motor difficulties in adolescence should be considered a risk factor for below-average bone strength and structure and fracture risk. Strategies are needed to improve bone health in this high-risk-group.

Improving health-related fitness in adolescents: the CrossFit Teens™ randomised controlled trial

The aim of this study was to evaluate the preliminary efficacy and feasibility of the CrossFit Teens™ resistance training programme for improving health-related fitness and resistance training skill competency in adolescents. This assessor-blinded randomised controlled trial was conducted in one secondary school in the Hunter Region, Australia, from July to September 2013. Ninety-six (96) students (age = 15.4 (.5) years, 51.5% female) were randomised into intervention (n = 51) or control (n = 45) conditions for 8-weeks (60 min twice per week). Waist circumference, body mass index (BMI), BMI-Z score (primary outcomes), cardiorespiratory fitness (shuttle run test), muscular fitness (standing jump, push-up, handgrip, curl-up test), flexibility (sit and reach) and resistance training skill competency were measured at baseline and immediate post-intervention. Feasibility measures of recruitment, retention, adherence and satisfaction were assessed. Significant group-by-time intervention effects were found for waist circumference [-3.1 cm, P < 0.001], BMI [-1.38 kg · m(‒)(2), P < 0.001], BMI-Z [-0.5 z-scores, P < 0.001], sit and reach [+3.0 cm, P < 0.001], standing jump [+0.1 m, P = 0.021] and shuttle run [+10.3 laps, P = 0.019]. Retention rate was 82.3%. All programme sessions were delivered and participants' mean satisfaction scores ranged from 4.2 to 4.6 out of 5. The findings demonstrate that CrossFit Teens™ is a feasible and efficacious programme for improving health-related fitness in adolescents.

Top 10 research questions related to musculoskeletal physical fitness testing in children and adolescents

The purpose of this article is to bring attention to the 10 most pressing questions relevant to musculoskeletal physical fitness testing in children and adolescents. The goal is to stimulate research to answer these questions. The most pressing needs include establishing definitive links between valid, reliable, and feasible field test measures of muscular strength, endurance, power, and flexibility and health risk factors/markers in children and adolescents; determining the effects of exercise training on these relationships; and documenting the tracking of these relationships. The role of flexibility in health-related physical fitness (HRPF) needs to be carefully and specifically examined. Although body weight/composition is a separate component of health-related fitness, it is also a factor that can influence the performance of musculoskeletal test items. The role of body weight, body fat, and central adiposity and the possibility of adjustment of tests results are important research questions. Several questions relate to which field tests are best for use in schools. Finally, actual health-related criterion-referenced cutoff values need to be developed. In conclusion, more quality research is needed to firmly establish the musculoskeletal area for HRPF in youth.

Effects of weight-bearing activities on bone mineral content and density in children and adolescents: a meta-analysis

Osteoporosis and associated fractures are a major health concern in Western industrialized nations. Exercise during growth is suggested to oppose the involutional bone loss later in life by increasing peak bone mass. The primary aim of the present meta-analysis was to provide a robust estimate of the effect of weight-bearing activities (WBAs) on bone mineral content (BMC) and areal bone mineral density (aBMD), during childhood and adolescence. To locate relevant studies up to June 2012, computerized searches of multiple bibliographic databases and hand searches of key journals and reference lists were performed. Results were extracted by two independent reviewers. The quality of the included trials was assessed via the Physiotherapy Evidence Database (PEDro) score. The study group effect was defined as the difference between the standardized mean change for the treatment and control groups divided by the pooled pretest SD. From 109 potentially relevant studies, only 27 met the inclusion criteria. The analyzed training programs were capable of significantly increasing BMC and aBMD during growth. However, the weighted overall effect sizes (ESs) for changes in BMC (ES 0.17; 95% confidence interval [CI], 0.05-0.29; p < 0.05) and aBMD (ES 0.26; 95% CI, 0.02-0.49) were small. Stepwise backward regression revealed that more than one-third of the observed variance (r(2)  = 0.35) between subgroups of the BMC dataset could be explained by differences in the amount of habitual calcium intake per day (beta 0.54, p < 0.01) and the maturational stage (beta -0.28, p < 0.01) at baseline. No significant moderators were identified for aBMD, possibly due to the small number of trials investigating WBAs on aBMD. The results of this meta-analysis conclude that WBAs alongside high calcium intake provide a practical, relevant method to significantly improve BMC in prepubertal children, justifying the application of this exercise form as an osteoporosis prophylaxis in this stage of maturity.

Sex-Related Effects in Strength Training during Adolescence: A Pilot Study

The objective was to investigate the effects of high-velocity strength training on isometric strength of the leg extensors and jump height in female and male adolescents. Twenty-eight students (13 boys, 15 girls) ages 16 to 17 years participated in this study and were assigned to either a strength training group or a control group. Strength training was conducted over 8 weeks (2 times per week). Pre- and post-training tests included the measurements of maximal isometric force and rate of force development of the leg extensors as well as countermovement jump height. Both girls (effect size = 1.37) and boys (effect size = 0.61) showed significant improvements in jump height. However, significant increases in maximal isometric force (effect size = 1.85) and rate of force development (effect size = 2.23) were found only in girls. In female and male adolescents, high-velocity strength training is an effective training regimen that produced improvements in countermovement jump height in both sexes but higher gains in maximal isometric force and rate of force development in girls.

Improving physical self-perception in adolescent boys from disadvantaged schools: psychological outcomes from the Physical Activity Leaders randomized controlled trial

OBJECTIVES

To evaluate the effect of a school-based obesity prevention programme on physical self-perception and key physical-activity related cognitions in adolescent boys from disadvantaged secondary schools. A secondary objective was to determine if any psychological changes were associated with improved weight status.

METHODS

Participants (n = 100, age = 14.3[0.6]) were randomized to the PALS (Physical Activity Leaders) intervention (n = 50) or a control group (n = 50) and assessed at baseline, 3- and 6-month follow up. Measures included BMI, BMI z-score and % body fat (bioelectrical impedance analysis). Students also completed the Children's Physical Self-Perception Profile and a physical activity-related cognitions questionnaire. The findings include secondary data analyses.

RESULTS

Relative to the controls, the PALS group significantly increased their physical self worth (p = .01), perceived physical condition (p = .02), resistance training self efficacy (p < .001) and their use of physical activity behavioural strategies (p = .02).

CONCLUSIONS

A school-based obesity prevention programme that targeted leadership skills improved psychological health in the physical domain in adolescent boys from disadvantaged schools.

Influence of exclusive resistance training on body composition and cardiovascular risk factors in overweight or obese children: a systematic review

OBJECTIVE

Since the last decade, a significant increase in the prevalence of overweight and obesity among children has been reported. Low aerobic fitness and a low compliance with endurance sports in such children are theoretical reasons to favor the use of resistance training in intervention studies, even though positive effects of resistance training on morbidity without accompanying dietary modifications are a matter of debate. In this review we summarize the studies that have shown the isolated effect of resistance training on body composition and cardiovascular risk factors in overweight and obese children.

METHOD

We systematically reviewed interventional studies that exclusively applied resistance training to overweight and obese 3- to 18-year-old children. Outcome measurements were body composition or cardiovascular risk factors.

RESULTS

Only six studies passed the inclusion criteria. All studies preferred an individually planned and supervised whole-body resistance training of moderate to submaximal intensity during treatment. The mean compliance was 84%. Four studies reported significant changes in body composition, with an increase in fat free mass and BMI, along with a decrease in fat mass. Three studies analyzed the effect of resistance training on cardiovascular risk factors, and only one study reported a significant decrease in systolic blood pressure.

CONCLUSION

An individually planned and supervised whole-body resistance training of moderate to submaximal intensity in children seems to be safe and tends to show positive effects on body composition. Similar to interventions based on endurance exercise alone or in combination with dietary modifications, the effects on cardiovascular risk factors cannot be substantiated. In consequence, we suggest to substantiate the effect of resistance training on cardiovascular risk factors in overweight and obese children in upcoming randomized controlled trials with high case numbers, applying both resistance training only and resistance training in combination with dietary intervention to get knowledge about whether resistance training alone is effectual in the treatment of overweight and obesity in youth or if a combination of resistance training and dietary interventions is actually needed.

Influence of resistance training on cardiorespiratory endurance and muscle power and strength in young athletes

The purpose of this study was to investigate the influence of additional resistance training on cardiorespiratory endurance in young (15.8 ± 0.8 yrs) male basketball players. Experimental group subjects (n=23) trained twice per week for 12 weeks using a variety of general free-weight and machine exercises designed for strength acquisition, beside ongoing regular basketball training program. Control group subject (n=23) participated only in basketball training program. Oxygen uptake (VO(2max)) and related gas exchange measures were determined continuously during maximal exercise test using an automated cardiopulmonary exercise system. Muscle power of the extensors and flexors was measured by a specific computerized tensiometer. Results from the experimental group (VO(2max) 51.6 ± 5.7 ml.min(-1).kg(-1) pre vs. 50.9 ± 5.4 ml.min(-1).kg(-1) post resistance training) showed no change (p>0.05) in cardiorespiratory endurance, while muscle strength and power of main muscle groups increased significantly. These data demonstrate no negative cardiorespiratory performance effects on adding resistance training to ongoing regular training program in young athletes.

Associations of physical activity with muscular fitness in adolescents

The aim of this study was to examine the associations between objectively assessed physical activity (PA) and muscular fitness (MF) in adolescents, and to determine whether only resistance training exercise is associated with the increase of MF. A sample of 211 Spanish adolescents (105 girls) wore the ActiGraph monitor for 7 days. Participants also completed a fitness evaluation including three MF tests (handgrip strength, a 60-s abdominal test and a standing broad jump), a cardiorespiratory fitness assessment and anthropometric measures. A standardized MF score was computed using the three muscular tests. Adolescent participation in resistance training was self-reported. Linear regression showed that only vigorous PA was significantly (P=0.041) and positively (β=0.133) associated with MF after adjustment by gender, age, pubertal status, BMI, and cardiorespiratory fitness. Significant differences in MF were found between youth in the lowest and upper tertiles of vigorous PA. Moreover, adolescents who were involved in resistance training had significantly higher MF scores compared with youth in low and medium tertiles of vigorous PA, but no significant differences were found when compared with non-lifters from the highest tertile of vigorous PA (P=0.356). These findings suggest that vigorous activity may be associated with indicators of MF in adolescents.

Resistance training for adolescents

The benefits and possible detriment of resistance training have been noted extensively in the literature. Although the benefits of resistance training are well known, many professionals fail to heed scientific advice or follow appropriate recommendations for resistance training in adolescents. When developing a resistance training program for adolescents, be cognizant of any pre-existing health conditions and experience level of the adolescent. For strength training, the adolescent should begin with exercises that involve all major muscle groups with relatively light weight, one to three sets of 6 to 15 repetitions, 2 to 3 non-consecutive days per week. As the adolescent becomes more experienced, gradually increase loads and add multijoint exercises. Each exercise session should be properly supervised for safety, and to provide feedback on technique and form, regardless of the resistance training experience of the adolescent. This article reviews the guidelines for resistance training for health-related fitness for adolescents.

Resistance training among young athletes: safety, efficacy and injury prevention effects

A literature review was employed to evaluate the current epidemiology of injury related to the safety and efficacy of youth resistance training. Several case study reports and retrospective questionnaires regarding resistance exercise and the competitive sports of weightlifting and powerlifting reveal that injuries have occurred in young lifters, although a majority can be classified as accidental. Lack of qualified instruction that underlies poor exercise technique and inappropriate training loads could explain, at least partly, some of the reported injuries. Current research indicates that resistance training can be a safe, effective and worthwhile activity for children and adolescents provided that qualified professionals supervise all training sessions and provide age-appropriate instruction on proper lifting procedures and safe training guidelines. Regular participation in a multifaceted resistance training programme that begins during the preseason and includes instruction on movement biomechanics may reduce the risk of sports-related injuries in young athletes. Strategies for enhancing the safety of youth resistance training are discussed.

Youth resistance training: updated position statement paper from the national strength and conditioning association

Faigenbaum, AD, Kraemer, WJ, Blimkie, CJR, Jeffreys, I, Micheli, LJ, Nitka, M, and Rowland, TW. Youth resistance training: Updated position statement paper from the National Strength and Conditioning Association. J Strength Cond Res 23(5): S60-S79, 2009-Current recommendations suggest that school-aged youth should participate daily in 60 minutes or more of moderate to vigorous physical activity that is developmentally appropriate and enjoyable and involves a variety of activities (). Not only is regular physical activity essential for normal growth and development, but also a physically active lifestyle during the pediatric years may help to reduce the risk of developing some chronic diseases later in life (). In addition to aerobic activities such as swimming and bicycling, research increasingly indicates that resistance training can offer unique benefits for children and adolescents when appropriately prescribed and supervised (). The qualified acceptance of youth resistance training by medical, fitness, and sport organizations is becoming universal ().Nowadays, comprehensive school-based programs are specifically designed to enhance health-related components of physical fitness, which include muscular strength (). In addition, the health club and sport conditioning industry is getting more involved in the youth fitness market. In the U.S.A., the number of health club members between the ages of 6 and 17 years continues to increase () and a growing number of private sport conditioning centers now cater to young athletes. Thus, as more children and adolescents resistance train in schools, health clubs, and sport training centers, it is imperative to determine safe, effective, and enjoyable practices by which resistance training can improve the health, fitness, and sports performance of younger populations.The National Strength and Conditioning Association (NSCA) recognizes and supports the premise that many of the benefits associated with adult resistance training programs are attainable by children and adolescents who follow age-specific resistance training guidelines. The NSCA published the first position statement paper on youth resistance training in 1985 () and revised this statement in 1996 (). The purpose of the present report is to update and clarify the 1996 recommendations on 4 major areas of importance. These topics include (a) the potential risks and concerns associated with youth resistance training, (b) the potential health and fitness benefits of youth resistance training, (c) the types and amount of resistance training needed by healthy children and adolescents, and (d) program design considerations for optimizing long-term training adaptations. The NSCA based this position statement paper on a comprehensive analysis of the pertinent scientific evidence regarding the anatomical, physiological, and psychosocial effects of youth resistance training. An expert panel of exercise scientists, physicians, and health/physical education teachers with clinical, practical, and research expertise regarding issues related to pediatric exercise science, sports medicine, and resistance training contributed to this statement. The NSCA Research Committee reviewed this report before the formal endorsement by the NSCA.For the purpose of this article, the term children refers to boys and girls who have not yet developed secondary sex characteristics (approximately up to the age of 11 years in girls and 13 years in boys; Tanner stages 1 and 2 of sexual maturation). This period of development is referred to as preadolescence. The term adolescence refers to a period between childhood and adulthood and includes girls aged 12-18 years and boys aged 14-18 years (Tanner stages 3 and 4 of sexual maturation). The terms youth and young athletes are broadly defined in this report to include both children and adolescents.By definition, the term resistance training refers to a specialized method of conditioning, which involves the progressive use of a wide range of resistive loads and a variety of training modalities designed to enhance health, fitness, and sports performance. Although the term resistance training, strength training, and weight training are sometimes used synonymously, the term resistance training encompasses a broader range of training modalities and a wider variety of training goals. The term weightlifting refers to a competitive sport that involves the performance of the snatch and clean and jerk lifts.This article builds on previous recommendations from the NSCA and should serve as the prevailing statement regarding youth resistance training. It is the current position of the NSCA that:

Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents

Many position stands and review papers have refuted the myths associated with resistance training (RT) in children and adolescents. With proper training methods, RT for children and adolescents can be relatively safe and improve overall health. The objective of this position paper and review is to highlight research and provide recommendations in aspects of RT that have not been extensively reported in the pediatric literature. In addition to the well-documented increases in muscular strength and endurance, RT has been used to improve function in pediatric patients with cystic fibrosis and cerebral palsy, as well as pediatric burn victims. Increases in children's muscular strength have been attributed primarily to neurological adaptations due to the disproportionately higher increase in muscle strength than in muscle size. Although most studies using anthropometric measures have not shown significant muscle hypertrophy in children, more sensitive measures such as magnetic resonance imaging and ultrasound have suggested hypertrophy may occur. There is no minimum age for RT for children. However, the training and instruction must be appropriate for children and adolescents, involving a proper warm-up, cool-down, and appropriate choice of exercises. It is recommended that low- to moderate-intensity resistance exercise should be done 2-3 times/week on non-consecutive days, with 1-2 sets initially, progressing to 4 sets of 8-15 repetitions for 8-12 exercises. These exercises can include more advanced movements such as Olympic-style lifting, plyometrics, and balance training, which can enhance strength, power, co-ordination, and balance. However, specific guidelines for these more advanced techniques need to be established for youth. In conclusion, an RT program that is within a child's or adolescent's capacity and involves gradual progression under qualified instruction and supervision with appropriately sized equipment can involve more advanced or intense RT exercises, which can lead to functional (i.e., muscular strength, endurance, power, balance, and co-ordination) and health benefits.

Cross-sectional investigation of indices of isokinetic leg strength in youth soccer players and untrained individuals

In this cross-sectional study, the differences in the isokinetic peak torque of the knee joint muscles (dominant and non-dominant) were investigated in three groups of youths (n=45; age, 14.9+/-1.1 years) with different soccer training backgrounds. Significant main effects were observed for training background on the functional hamstrings to quadriceps ratios for knee flexion (H(CON):Q(ECC) ratio; F(2,42)=4.023, P=0.025) and extension (H(ECC):Q(CON) ratio; F(2,42)=8.53, P<0.001) at 4.32 rad/s. Post hoc tests indicated that both ratios were significantly different between conventionally trained players compared with resistance-trained players and controls (mean+/-SD; H(ECC):Q(CON) ratio, dominant limb; 0.91+/-0.10; 1.04+/-0.12; 1.10+/-0.22; non-dominant limb; 0.89+/-0.09; 1.05+/-0.19; 1.06+/-0.15; H(CON):Q(ECC) ratio, dominant limb; 0.36+/-0.06; 0.34+/-0.07; 0.30+/-0.08; non-dominant limb; 0.33+/-0.05; 0.32+/-0.08; 0.28+/-0.07). Results suggest that the muscle-loading patterns experienced in youth soccer may alter the reciprocal balance of strength about the knee under high-velocity conditions. The findings also indicate that these balances may be improved by incorporating resistance training into the habitual exercise routines of youth soccer players.

Physical activity behaviors and emotional self-efficacy: is there a relationship for adolescents?

BACKGROUND

This study explored relationships between physical activity (PA) behaviors and emotional self-efficacy (ESE) in a statewide sample of public high school adolescents in South Carolina (n=3836).

METHODS

The Center for Disease Control Youth Risk Behavior Survey PA items and an adolescent ESE scale were used. Logistic regression analyses and multivariate models constructed separately, revealed significant race by gender findings.

RESULTS

Results suggest that reduced vigorous PA (past 7 days), moderate PA (past 7 days), strengthening/toning exercises (past 7 days), and playing on sport teams (past 12 months) were associated (p<or=.05) with reduced ESE for specific race/gender groups.

CONCLUSIONS

Results have implications for school- and community-based mental health services and PA programs for adolescents. Measures of ESE as a component of comprehensive assessments of adolescent mental health and PA behaviors in fieldwork, research, and program-evaluation efforts should be considered.

Effects of resistance training on metabolic fitness in children and adolescents: a systematic review

The majority of resistance training (RT) research with children to date has focused on pre-adolescents and the safety and efficacy of this type of training rather than the potential metabolic health benefits. Our objectives, using computerized databases, were (i) to systematically review studies utilizing RT interventions with children and adolescents <18 years; (ii) to investigate the metabolic health outcomes (adiposity, lipids, insulin, glucose) associated with RT; (iii) to provide recommendations for future investigations. A total of 12 studies met the review criteria. There is only a small amount of evidence that children and adolescents may derive metabolic health-related adaptations from supervised RT. However, methodological limitations within the body of this literature make it difficult to determine the optimal RT prescription for metabolic fitness in children and adolescents, and the extent and duration of such benefits. More robustly designed single modality randomized controlled trials utilizing standardized reporting and precise outcome assessments are required to determine the extent of health outcomes attributable solely to RT and to enable the development of evidence-based obesity prevention and treatment strategies in this cohort.

Preliminary evaluation of an after-school resistance training program for improving physical fitness in middle school-age boys

Most after-school physical activity programs for youth focus on aerobic games and activities. The purpose of this study was to evaluate the efficacy of an after-school resistance training program on improving the physical fitness of middle school-age boys. 22 boys (M = 13.9 yr., SD = .4 yr.) participated in a periodized, multiple-set, 9-wk. (2x/week) resistance training program. All subjects were pre- and post-tested on their 10-repetition maximum squat, 10-repetition maximum bench press, vertical jump, medicine ball toss, flexibility, and also percentage of body fat and the progressive aerobic cardiovascular endurance run (PACER). Statistical analysis indicated that subjects significantly improved performance on the squat (19%), bench press (15%), flexibility (10%), vertical jump (5%), medicine ball toss (12%), and the PACER (36%). Although this design minus a control group limits interpretation, this after-school resistance-training program can improve muscular fitness and cardiovascular fitness in boys and should be replicated with appropriate experimental controls.