Physiological and Performance Adaptations in Athletically Trained Children Over a 24 Week Period

Abstract

This thesis assessed the validity and reliability of wireless near infrared spectrometry for monitoring muscle oxygenation during exercise in children. Additionally, it also observed the physiological and performance developments of children participating in club-based athletic training.
Study One represented the first attempt to investigate criterion validity and intra-unit reliability of the Moxy wireless near infrared spectroscopy monitor during exercise in children. Fourteen children, 9 males (aged 9.67 ± 0.52 years) and 5 females (aged 9.87 ± 0.68 years) participated in the study. Muscle oxygenation was measured during treadmill running at 4, 6 and 8 km.h-1 with the Moxy and with the NIRO-200 laboratory-based system. At 4 km.h-1 the Moxy recorded higher mean muscle oxygenation than the NIRO-200 (62.16 ± 8.1 compared to 59.61 ± 5.2), whilst at 6 km.h-1 the NIRO-200 measured higher mean values than the Moxy (59.90 ± 7.6 compared to 61.05 ± 6.1). At 8 km.h-1 mean values were 59.46 ± 8.7 for the Moxy and 59.25 ± 5.4 for the NIRO (Figure 1). No significant difference was found muscle oxygenation measures recorded by the Moxy compared to the NIRO-200 (F(1, 78) = .44, p= .508, η2= .006). Whilst Bland Altman analysis showed positive mean differences of 3.17%, 1.32% and 0.50% at 4 km.h-1, 6 km.h-1 and 8 km.h-1 respectively, 96% of data points fell within limits of agreement. Additionally, strong correlation was evident at 8 km.h-1 (r = .800, P< .05) but only moderate at 4 km.h-1 (r = .351, P< .05) and 6 km.h-1 (r = .497, P< .05) showing that the Moxy measures muscle oxygenation closer to the criterion measure at higher running speeds in children. The Moxy demonstrated intra-unit reliability through CV values of 5% at 4 km.h-1 and 6 km.h-1. Strong ICC values were also evident at 4 km.h-1 (r = .809, P< .001) and 6 km.h-1 (r = .834, P< .001). At 8 km.h-1 CV improved to 3% and ICC categorised as almost perfect (r = .940, P< .001). Intra-unit reliability values from the Moxy were strong and therefore this suggests that this wireless monitor can reliably monitor longitudinal changes in muscle oxygenation. In conclusion, the Moxy NIRS monitor provides a valid and reliable a tool for monitoring muscle oxygenation during running activity in children.
Study Two observed the physiological and performance development of eighteen children, 10 males (aged 9.67 ± 0.87) and 8 females (aged 9.56 ± 0.53), who participated in athletic training. This study also introduced the novel observation of 24 weeks of exercise in addition to the first use of wireless near infrared spectroscopy technology to observe longitudinal changes in muscle oxygenation in children. After 24 weeks, 10 metre (ES = 0.48), 20 metre (ES = 0.73) and 40 metre (ES = 0.73) sprint times were significantly faster and jump height significantly higher (ES = 0.43), whilst no change was recorded on fat free mass, calf or thigh circumference. After 24 weeks, 400 metre (ES = 0.25) run time was significantly faster with measures of muscle oxygenation showing mean muscle oxygenation significantly higher (ES = 0.78), deoxygenation half-relaxation time (THR) significantly faster (ES = 0.19) and actual muscle oxygenation values recorded at THR significantly higher (ES = 0.78). Deoxygenation half-relaxation time and mean SmO2 were found to demonstrate significant change only between weeks 12 to 24. Pre-run muscle oxygenation showed no change. In conclusion, the study found that 24 weeks of athletic training resulted in beneficial improvements to sprint and jump performance. Different temporal patterns were evident for jump performance that matched previous research but not for the acceleration phase of the sprint. The first use of a wireless NIRS monitor to measure longitudinally found significant and beneficial changes in muscle oxygenation over 24 weeks that may indicate an improvement in the ability to supply and remove oxygen from the blood during exercise, with the significant change occurring from 12 to 24 weeks.