Lower-body strength,power and sprint front crawl performance

Purpose To determine the association between lower-body strength and lower-body power capacities with sprint swimming performance in adolescent competitive swimmers.Methods A total of 44 front crawl swimmers(27 males and 17 females)performed anthropometric assessments,lower-body strength tests(half squat maximum isometric strength,dynamic half squat with 20,30 and 40%of the maximum isometric strength,and knee extension maximum isometric strength)and lower-body power tests(squat jump[SJ],countermovement jump[CMJ]and Abalakov jump).Further front crawl swimming best times in 50 and 100 m were recorded from official swimming competitions and front crawl technique was assessed by an experienced coach using a visual analogue scale.Results Swimming performance was correlated with lower-body power variables(SJ[r=−0.573 for 50 m and−0.642 for 100 m],CMJ[r=−0.497 for 50 m and−0.544 for 100 m],and Abalakov jump[r=−0.452 for 50 m and−0.415 for 100 m];p≤0.05)and lower-body strength(half squat maximum isometric strength[r=−0.430 for 50 m and−0.443 for 100 m];p≤0.05)in males but not in females.Further linear regression models showed that only lower-body power predicted both 50 m(Abalakov jump;r^(2)=0.58;change in r^(2)=0.18)and 100 m(SJ;r^(2)=0.66;change in r^(2)=0.15)performance in male swimmers.Conclusions This study emphasizes the greater association between lower-body power and sprint front crawl performance in adolescent males compared to females.Practical tests(i.e.,SJ and Abalakov jump)are shown to predict front crawl swimming performance,which may facilitate the performance control by coaches and trainers.

Plyometric exercise and bone health in children and adolescents: a systematic review

Background:Many jumping interventions have been performed in children and adolescents in order to improve bone-related variables and thus,ensure a healthy bone development during these periods and later in life.This systematic review aims to summarize and update present knowledge regarding the effects that jumping interventions may have on bone mass,structure and metabolism in order to ascertain the efficacy and durability (duration of the effects caused by the intervention) of the interventions.Data sources:Identification of studies was performed by searching in the database MEDLINE/PubMed and SportDiscus.Additional studies were identified by contacting clinical experts and searching bibliographies and abstracts.Search terms included 'bone and bones','jump*','weight-bearing','resistance training' and 'school intervention'.The search was conducted up to October 2014.Only studies that had performed a specific jumping intervention in under 18-year olds and had measured bone mass were included.Independent extraction of articles was done by 2 authors using predefined data fields.Results:A total of 26 studies were included in this review.Twenty-four studies found positive results as subjects included in the intervention groups showed higher bone mineral density,bone mineral content and bone structure improvements than controls.Only two studies found no effects on bone mass after a 10-week and 9-month intervention.Moreover,those studies that evaluated the durability of the effects found that some of the increases in the intervention groups were maintained after several years.Conclusions:Jumping interventions during childhood and adolescence improve bone mineral content,density and structural properties without side effects.These type of interventions should be therefore implemented when possible in order to increase bone mass in early stages of life,which may have a direct preventive effect on bone diseases like osteoporosis later in fife.