Chronic Physiological Effects of Swim Training Interventions in Non-Elite Swimmers: A Systematic Review and Meta-Analysis.

BACKGROUND: Swimming is a popular and potentially health-enhancing exercise, but has received less scientific attention compared with other exercise modes.
OBJECTIVE: The objective of the study was to determine the chronic (long-term) effect of pool swim training on physiological outcomes in non-elite or non-competitive swimming participants.
DESIGN: This study was a systematic review with a meta-analysis. DATA SOURCES: We searched the electronic databases PubMed, EMBASE and CENTRAL from inception to March 2017. ELIGIBILITY CRITERIA: The eligibility criteria included randomised controlled trials, quasi-randomised controlled trials and controlled trials of chronic (long-term) swimming interventions in non-elite or non-competitive swimming participants, with a physiological outcome measure.
RESULTS: Our search of 6712 records revealed 29 eligible studies. Swimming had a significant and clinically meaningful effect on maximal oxygen uptake compared with the control in an analysis including multiple populations (mean difference 6.32 mL/kg/min; 95% confidence interval 4.33-8.31), and subgroup analyses of healthy children/adolescents (mean difference 7.93 mL/kg/min; 95% confidence interval 3.31-12.55) and those with asthma (mean difference 9.67 mL/kg/min; 95% confidence interval 5.84-13.51) and healthy adults (mean difference 5.87 mL/kg/min; 95% confidence interval 2.93-8.81). Swimming also resulted in significant improvements in other cardiorespiratory fitness-related outcomes such as maximal minute ventilation (mean difference 0.61 L/min; 95% confidence interval 0.17-1.05), submaximal exercise performance (standardised mean difference 0.64; 95% confidence interval 0.14-1.13) and total exercise test time (mean difference 4.27 min; 95% confidence interval 2.11-6.42). Compared with the control, swimming had significant favourable effects on body mass (mean difference - 2.90 kg, 95% confidence interval - 5.02 to - 0.78), body fat percentage in multiple populations (mean difference - 1.92%; 95% confidence interval - 3.25 to - 0.60) and healthy children/adolescents (mean difference - 1.92%; 95% confidence interval - 4.64 to - 0.80) and lean mass (mean difference 1.96 kg; 95% confidence interval 0.21-3.71), but negative effects on waist circumference in a pooled analysis of two studies involving adults with hypertension (mean difference 4.03 cm; 95% confidence interval 2.58-5.49). Regarding lung function, significant effects of swimming vs. the control were found only for peak expiratory volume in analyses including children/adolescents combined with healthy adults (mean difference 58.74 L/min; 95% confidence interval 29.70-87.78) and children/adolescents with asthma alone (mean difference 63.49 L/min; 95% confidence interval 25.01-101.97). Based on limited data, swimming had similar effects to other exercise modes, except for higher post-intervention body mass index values with swimming vs. running in healthy adults (mean difference 1.18 kg/m2; 95% confidence interval 0.54-1.81).
CONCLUSIONS: Swimming may offer robust beneficial effects on cardiorespiratory fitness and body composition across multiple populations and effects may be comparable to other exercise modes. Future randomised controlled trials are required to establish the effectiveness of swimming on physiological outcomes in healthy populations and those with non-communicable disease.