Effectiveness of strength training interventions on adolescent backstroke swimming performance

Abstract

The scientific literature on swimming often states swimming performance is highly influenced by the strength and muscular power of the upper and lower body. To reduce injury risk and enhance swimming performance, coaches invariably include strength training on land (dryland) or in-water (resisted swimming) as part of their swimmers’ training programmes to further complement actual in-water swimming training. Despite the popularity of strength training prescribed to enhance performance, the quantification of its effectiveness in improving adolescent backstroke performance has received scant scientific attention. The World Health Organization (WHO) defines an adolescent as any person between ages 10 and 19 years old. Physically, the adolescent stage of life is characterised by rapid changes in body size, shape and growth, during which a young person develops from a child to an adult (Howells, 2018). Due to these changes, rather than applying study findings derived from adults, it is important to understand the influence any strength training intervention has specifically on adolescent performance. Therefore, this thesis seeks to determine the extent to which dryland and in-water strength training practices may be beneficial for adolescent backstroke swimmers.

My thesis is composed of four studies addressing performance analysis (Study 1), dryland (Study 2 and Study 3) and in-water strength training (Study 4) interventions of adolescent backstroke swimmers. Using retrospective analysis, Study 1 quantified the annual change in competition performance as backstroke swimmers matured. Almost 10,000 swimming years of accumulated data from New Zealand based swimmers was used to estimate the rate of improvement of male and female swimmers as they aged from 8 to 18 years. Our data set highlighted that swimmers improve their performance times by ~1/3 with a decade of backstroke swimming training (in association with natural growth and maturation processes). During the early competitive years (ages 8 – 10) it is not uncommon to improve close to 10% annually. However, during the middle years (ages 11 – 14) improvements of ~5% are realised, while in the later years (ages 15 – 18) improvements of only 1 – 2% are achieved.

Performance improved with increasing age and we know that strength increases as a function of age, therefore many studies have correlated grip strength with improved sports performance because grip strength is an indicator of overall body strength. Using a randomised controlled trial, Study 2 primarily investigated whether improved grip strength would enhance adolescent 100 m backstroke performance. In addition to 4 hours per week of swimming training, undertaking grip strength training (5 min/session, 4x/week for 8 weeks) successfully improved isometric grip strength by 30 – 36% in the two treatment groups (Powerball n=9, age 11.5 ± 1.6 y, 6 male, 3 female: Stressball n= 8, age 11.6 ± 1.6 y, 5 male, 3 female). Despite this improved grip strength, 100 m backstroke time did not improve. Notably, this was the first training study to quantify grip strength’s effect on backstroke performance.

As higher overall strength has been linked with faster sprinting performance using a randomised controlled trial with 28 adolescent male swimmers (age: 12.6 ± 2.6 years), Study 3 primarily examined whether improved overall strength from a beginners’ dryland training programme (~30 min/session, 3x/week for 8 weeks) would improve 50 and 100 m backstroke performance. Over 8 weeks, the Dryland strength group had small to large strength gains of 13 – 167%. These strength gains transferred to small 4.4% and trivial 1.6% magnitude faster 50 and 100 m backstroke performances, respectively. Importantly, our study showed dryland strength transfer was more