The effects of yoga on sports performance and health : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

Stretching is frequently used in an attempt to increase flexibility and enhance athletic performance. Stretching and similar techniques have also been used in sedentary and clinical populations to increase the mobility of joints, reduce pain and improve cardiovascular health. Yoga is not only a stretching exercise but uses a holistic approach that improves flexibility and incorporates mental awareness. However, yoga has seldom been investigated in elite athletes or a representative cross-section of society. In the first three studies of this research, a yoga intervention was employed to assess the influence of yoga on flexibility, balance, and sport performance (i.e. sprinting ability) in rugby players. Furthermore, in a fourth, large, cross-sectional study, I examined the effects of practising yoga on cardiovascular health markers (total cholesterol, blood glucose, heart-rate variability (HRV), and arterial stiffness) in healthy adults. Findings in the first study suggest that two, 1 hr yoga sessions per week for 12 weeks resulted in a significantly reduced postural sway signal in the 2-legged eyes closed antero-posterior (-109.7% ± 82.9) and medial-lateral (-115.5% ± 92.1, mean ± 95% CI, p<0.005) directions in a yoga group (n = 15) compared to a control group (n = 14), indicating an improved balance ability in rugby players. In the second study, incorporating 8 weeks of yoga, including two, 1 hr sessions per week I found a minor, non-significant improvement in split times in the yoga group (-3.2% ± 10.4, -0.7% ± 9.0 for the 5 and 10 m sprints respectively, mean ± 95% confidence interval) compared to controls (-0.4% ± 10.2, 0.4% ± 7.9). Additionally, no significant change was found in the flexibility of the yoga group but the control group significantly decreased flexibility over this period. Based on the results of the first two studies (two, 1 hr yoga sessions either over 8 or 12 weeks resulting in minor changes to balance and performance in the male rugby players), a decision was made to investigate a more concise intervention that included shorter yoga sessions (better fit into busy schedules of players), included advanced postures, and had quick progressions through postures to determine if a more practical intervention could be equally effective for players. In the third study, a new yoga intervention which included advanced postures with a shorter session time (2 sessions/week for 30 min each, rather than 1 hr each) over a similar time frame (12 weeks) was carried out to observe the effects of yoga on flexibility measured at the hip and knee and sprint performance (over 5, 10, 15 and 20 m) in female rugby players. The five players in the yoga intervention group demonstrated significantly improved straight leg raises 29.1 ± 15.3 degrees (mean % change ± 95% CI, p < 0.05) compared to the control group 2.9 ± 18.6 (mean % change ± 95% CI, p > 0.05). Players in the yoga group also significantly improved their 5 m sprint time -10.4 ± 10.2 (mean % change ± 95% CI, p < 0.05) compared to the control group 9.9 ± 6.1 (mean % change ± 95% CI, p > 0.05), suggesting that yoga may help female rugby players improve or at least maintain their sprint performance and flexibility during the season. Yoga has also been associated with health improvements, particularly for the cardiovascular system. In the fourth study, the associations between yoga and clinical measures of cardiovascular health was investigated in a large cross-sectional study. New Zealand adult participants were split into those that regularly practised yoga and those that did not. Overall, the regularly-practicing yoga participants had significantly lower carotid-femoral pulse wave velocity (-0.13 ± 0.28, m.s-1, p < 0.05, mean ± 95% CI) and systolic blood pressure (-2.0 ± 2.6, mmHg, p < 0.05), higher flexibility (12.7 ± 1.9 cm, p < 0.01), and higher total physical activity levels (1035.1 ± 671.3 METmin.week-1, p < 0.01) compared to the control group not practicing yoga. The control group was significantly taller (2.7 ± 1.7 cm, mean ± 95% CI, p < 0.002), heavier (8.2 ± 4.1 kg, p < 0.01), had more muscle mass (2.9 ± 1.5 kg, p < 0.05), higher body mass index (2.0 ± 0.7, p < 0.05), higher waist-hip-ratio (0.05 ± 0.02 cm, p < 0.01), and higher body fat (2.9 ± 3.1 kg) than the yoga group. Furthermore, the control group had higher blood glucose levels (92.0 ± 15.2 mg/dl) compared to the yoga group (90.6 ± 13.8 mg/dL, p = 0.36), but the yoga group had higher total cholesterol compared to the control group (192.1 ± 40.5 and 176.7 ± 42.8 mg/dL mean ± SD, for yoga group and control group respectively, p < 0.01). When the groups were separated into age categories the carotid-femoral pulse wave velocity was found to be significantly lower in younger (18 to 39 years) and older (60 years and above) yoga participants compared to controls. The findings suggest that regular practice of yoga is associated with reduced carotid-femoral pulse wave velocity and improved clinical measures of cardiovascular health. Overall, yoga appears to improve the flexibility of those who regularly practice it (i.e. 1 x per week) over a long time period (i.e. 3-months). In particular, yoga was found to be associated with improved eyes closed balance in rugby players and either maintained or improved 5 m sprint performance and improved some cardiovascular health indices among healthy adults. Overall, improved flexibility may be useful for daily physical functioning and for maintaining lifelong physical activity among the general population and for sport performance of athletes.