Female athletes exhibit three- to six-fold greater incidence of noncontact anterior cruciate ligament (ACL) injury relative to their male counterparts. The increased risk appears to stem from interactions between several risk factors, that can roughly be categorized as anatomic, biomechanical, hormonal, and neuromuscular. Neuromuscular risk factors have recently gained a greater focus, and include differences in the timing and magnitude of activation of lower extremity and trunk musculature. In addition to neuromuscular risk factors, the incidence of ACL injury is not evenly distributed across the menstrual cycle, suggesting that hormonal fluctuations may influence neuromuscular control. Finally, it is known that even well-trained athletes experience decrements in performance and postural control when forced to attend to multiple sensory stimuli, which is common in many sports. PURPOSE: To explore neuromuscular differences in the ways healthy and ACL-injured women respond to a secondary task requiring fine motor control and sustained mental focus (typing task). Our investigation encompassed three broad aims. First, we sought to determine whether ACL-injured individuals demonstrated similar reflex profiles to healthy individuals, as well as to determine whether the ACL-involved limb was similar to its uninvolved counterpart. Our second aim was to determine whether the typing task resulted in attenuated Hoffmann (H) reflex amplitudes, and to investigate whether any observed changes were similar in healthy and ACL-injured groups. Finally, our third broad aim was to utilize more complex H reflex analysis techniques to determine whether differences in spinal excitability existed at different points in the menstrual cycle. METHODS: Thirty nine recreationally active women (20 with prior unilateral noncontact ACL injury: 24.0 ± 4.5 years; 23.8 ± 4.5 kg•m⁻²; 4.1 ± 2.6 years post-injury; 19 with no history of knee injury: 23.8 ± 4.5 years; 23.1 ± 2.3 kg•m⁻²) agreed to participate, and were tested during days 2-5 (follicular phase) of the menstrual cycle. A sub-set of this original group (n=8; 24.0 ± 4.8 years; 22.0 ± 2.1 kg•m⁻²) also agreed to return for a second testing session 24-96 hours after ovulation (early luteal phase), in order to assess H reflex differences across the menstrual cycle. During each testing session, H reflex testing was used to explore spinal-level control mechanisms of the lower extremity musculature under both Rest and Task conditions. In the control group, the dominant limb was tested (CON-D) while in the ACL group, both the uninvolved (ACL-UN) and involved (ACL-INV) limbs were assessed. Differences between groups (Control vs. ACL) and within-groups (ACL-UN vs. ACL-INV) were explored. RESULTS: At rest, H reflex parameters in ACL-INV were generally similar to ACL-UN and to CON-D. However, differences in presynaptic inhibition were apparent in ACL-INV that imply reduced reflex plasticity. During the typing task, both the Control and ACL groups experienced attenuated H reflex parameters. In the sub-set of participants who were tested twice during the menstrual cycle, a significant increase in presynaptic inhibition was observed during the early luteal phase compared to the follicular phase. CONCLUSION: While individuals with prior ACL injury display similar H reflex profiles to healthy individuals, the ACL-involved limb may demonstrate less reflex plasticity in response to environmental changes. This lack of plasticity may potentially increase the risk of re-injury. In addition, an upper extremity task requiring fine motor control and sustained mental focus attenuates the H reflex in both groups. This attenuation has implications for lower-extremity neuromuscular control in dual-task environments. Finally, the increase in presynaptic inhibition observed during the early luteal phase may provide insight into why ACL injuries are not evenly distributed across the menstrual cycle. / Graduation date: 2012

[Truncated abstract] Broadly, research literature on the physiological aspects of water polo game play is limited, but particularly so in the women's game. Moreover, significant changes to game rules in recent years are likely to have had an impact on the game demands. Therefore, this research project sought to investigate the physiological characteristics of contemporary elite female water polo players and the demands of match play. Overall, the five studies comprising this thesis aimed to improve the practical knowledge of coaches and sport scientists concerning the training and monitoring of players. Study one (Chapter 3) compared two water polo-specific field tests of aerobic and/or match fitness (MSST, multistage shuttle swim test; and WIST, water polo intermittent shuttle test) with a traditional incremental swimming test to exhaustion (IST, 5 x 200 m). Prior to this study, the physiological responses to the MSST and WIST were not well understood. Additionally, the degree of association between these two tests was unknown. Therefore, 14 Australian National Women's Water Polo Squad players performed the MSST and WIST, and 13 players from a National Water Polo League club performed the MSST, WIST and IST, on separate occasions. Peak heart rate, blood lactate and ratings of perceived exertion were obtained for all tests. Expired air was collected post test for the National League players. The results showed that the National Squad players performed significantly better in the MSST (636 ± 114 vs. 437 ± 118 m, p < 0.001) and WIST (270 ± 117 vs. 115 ± 57 m, p < 0.001) than the National League players. ... Absolute decrement yielded TE of 0.55 s (-0.42-0.81), CV of 26.0% (19.3-41.0) and ICC of -0.002 (-0.44-0.44). Relative (%) decrement yielded TE of 1.6% (1.2-2.3), CV of 27.2% (20.1-42.9) and ICC of -0.02 (-0.46-0.42). Results indicate that total time was a reliable measure, whilst decrement was not. Similar to land-based RSA tests, total time should be the criterion measure of performance in the RST. The RST can form part of a specific battery of field tests for water polo, and can also be used as a conditioning tool. The final study (Chapter 7) was a nutritional-intervention study. Based on the time-motion data from study three, a 59-min match simulation test (MST) was designed to mimic the activity profiles and physical demands of water polo match play. Using a randomized cross-over double-blind design, 12 Australian National Women's Water Polo Squad players ingested 0.3 g·kg-1 of NaHCO3 or placebo, 90 min before performing the MST, which included 56 x 10-m maximal-sprint swims as the performance measure. Although pre-exercise ingestion of NaHCO3 was effective in enhancing extracellular pH and bicarbonate levels, the percentage difference in mean sprint times between trials showed no substantial effects of NaHCO3 (0.4; ±0.9%, effect size = 0.09; ±0.23, p = 0.51). The results suggest that elite water polo players should not expect enhancement in intermittent-sprint performance from NaHCO3 supplementation. These findings are contrary to previous NaHCO3 studies on simulated team-sport performance, but this investigation is unique in that it examined highly-trained athletes performing sport-specific tasks. In conclusion, the findings of this thesis add to the existing literature on the applied physiology of women's water polo. It is hoped that the knowledge gained from these findings will lead to more appropriate conditioning, testing and selection outcomes.