Scott Newbould

This project aimed to investigate the muscle-tendon unit (MTU) properties of female athletes in response to chronic loading and the menstrual cycle. To achieve this, this thesis includes studies investigating the between-day reliability of MTU metrics, the variability of these metrics over the menstrual cycle, and the MTU properties of female athletes who have undergone different types of chronic loading: netball and running. Regarding reliability, global performance metrics generally displayed higher reliability than local measures of MTU function. Over the menstrual cycle, isometric knee extension strength was greater in Phase 4 than Phase 1, and impulse at 50 ms in the isometric midthigh pull was greater in Phase 1 than Phase 4. These phase-based findings were corroborated by relationships between hormones and these metrics, however, the magnitude of change of these variables was smaller than the minimum detectable change calculated from the reliability data. Across two cycles, the Mid-cycle phase displayed the highest reproducibility of MTU assessments. Menstrual cycle symptoms were higher in Phase 1 than both other phases, and symptoms were negatively related to countermovement and drop jump performance. When comparing netballers and runners, netball athletes had greater Achilles’ and patellar tendon thicknesses, Achilles’ tendon stiffness, and knee extension and plantar flexion strength. Overall, this project has shown that MTU function is affected by hormone and symptom changes throughout the menstrual cycle and that female MTU properties are adaptable to chronic loading. The reliability and menstrual cycle data can be used to inform metric selection and better interpret other female athlete MTU data, and this work highlights the importance of assessing symptoms alongside hormones and objective MTU metrics when investigating different hormonal environments. Finally, the data reported for netballers and runners can be used to inform training prescription to enhance performance and mitigate injury risk in female athletes.

Abstract

Measurements of muscle-tendon unit (MTU) function can be categorised into local (e.g. tendon strain) or global (e.g. jump height) assessments. Although menstrual cycle phase may be a key consideration when implementing these assessments in female athletes, the reliability of many MTU assessments is not well defined within female populations. Therefore, the purpose of this study was to report the test-retest reliability of local and global MTU function assessments during the early follicular phase of the menstrual cycle. Seventeen naturally menstruating females (age 28.5 ± 7.3 years) completed local and global assessments of MTU function during two testing sessions separated over 24-72 hours. Local tests included Achilles’ tendon mechanical testing and isometric strength of ankle plantar flexors and knee extensors, whereas global tests included countermovement, squat, and drop jumps, and the isometric midthigh pull. Based on intraclass correlation coefficient (ICC) statistics, poor to excellent reliability was found for local measures (ICC: 0.096-0.936). Good to excellent reliability was found for all global measures (ICC: 0.788-0.985), excluding the eccentric utilisation ratio (ICC 0.738) and most rate of force development metrics (ICC: 0.635-0.912). Isometric midthigh pull peak force displayed excellent reliability (ICC: 0.966), whereas force-time metrics ranged from moderate to excellent (ICC: 0.635-0.970). Excluding rate of force development (coefficient of variation [CV]: 10.6-35.9%), global measures (CV: 1.6-12.9%) were more reproducible than local measures (CV: 3.6-64.5%). However, local metrics directly measure specific aspects of MTU function, and therefore provide valuable information despite lower reproducibility. The novel data reported here provides insight into the natural variability of MTU function within female athletes, which can be used to enhance the interpretation of other female athlete data, especially that which aims to investigate other aspects of variability, such as the menstrual cycle.

Muscle-tendon unit (MTU) assessments can be categorised into local (e.g., tendon strain) or global (e.g., jump height) assessments. Although menstrual cycle phase may be a key consideration when implementing these assessments in female athletes, the reliability of many MTU assessments is not well defined within female populations. Therefore, the purpose of this study was to report the test-retest reliability of local and global MTU assessments during the early follicular phase of the menstrual cycle. Seventeen naturally menstruating females (age 28.5 ± 7.3 years) completed local and global MTU assessments during two testing sessions separated over 24–72 hours. Local tests included Achilles’ tendon mechanical testing and isometric strength of ankle plantar flexors and knee extensors, whereas global tests included countermovement, squat, and drop jumps, and the isometric midthigh pull. Based on intraclass correlation coefficient (ICC) statistics, poor to excellent reliability was found for local measures (ICC: 0.096–0.936). Good to excellent reliability was found for all global measures (ICC: 0.788–0.985), excluding the eccentric utilisation ratio (ICC 0.738) and most rate of force development metrics (ICC: 0.635–0.912). Isometric midthigh pull peak force displayed excellent reliability (ICC: 0.966), whereas force-time metrics ranged from moderate to excellent (ICC: 0.635–0.970). Excluding rate of force development (coefficient of variation [CV]: 10.6–35.9%), global measures (CV: 1.6–12.9%) were more reproducible than local measures (CV: 3.6–64.5%). However, local metrics directly measure specific properties of the MTU, and therefore provide valuable information despite lower reproducibility. The novel data reported here provides insight into the natural variability of MTU assessments within female athletes which can be used to enhance the interpretation of other female athlete data, especially that which aims to investigate other aspects of variability, such as the menstrual cycle.

Muscle-tendon unit (MTU) assessments can be categorised into local (e.g. tendon strain) or global (e.g. jump height) assessments. Although menstrual cycle phase may be a key consideration when implementing these assessments in female athletes, the reliability of many MTU assessments is not well defined within female populations. Therefore, the purpose of this study was to report the test-retest reliability of local and global MTU assessments during the early follicular phase of the menstrual cycle. Seventeen naturally menstruating females (age 28.5 ± 7.3 years) completed local and global MTU assessments during two testing sessions separated over 24-72 hours. Local tests included Achilles’ tendon mechanical testing and isometric strength of ankle plantar flexors and knee extensors, whereas global tests included countermovement, squat, and drop jumps, and the isometric midthigh pull. Based on intraclass correlation coefficient (ICC) statistics, poor to excellent reliability was found for local measures (ICC: 0.096-0.936). Good to excellent reliability was found for all global measures (ICC: 0.788-0.985), excluding the eccentric utilisation ratio (ICC 0.738) and most rate of force development metrics (ICC: 0.635-0.912). Isometric midthigh pull peak force displayed excellent reliability (ICC: 0.966), whereas force-time metrics ranged from moderate to excellent (ICC: 0.635-0.970). Excluding rate of force development (coefficient of variation [CV]: 10.6-35.9%), global measures (CV: 1.6-12.9%) were more reproducible than local measures (CV: 3.6-64.5%). However, local metrics directly measure specific properties of the MTU, and therefore provide valuable information despite lower reproducibility. The novel data reported here provides insight into the natural variability of MTU assessments within female athletes, which can be used to enhance the interpretation of other female athlete data, especially that which aims to investigate other aspects of variability, such as the menstrual cycle.

Muscle-tendon function can be categorised into “energy conservation” or “power modulation” tasks. However, little is known about how female tendons adapt to these different loading demands. This study compared muscle-tendon unit morphological and mechanical properties in athletes who regularly undergo either energy conservation (14 runners) or power modulation (eight netballers) activities. Static ultrasound was used to measure Achilles’ and patellar tendon thickness, as well as the thickness, pennation angle, and fascicle length of the gastrocnemii and vastus lateralis muscles. Achilles’ tendon length and moment arm were also measured. Muscle-tendon mechanical measures included plantar flexion and knee extension isometric strength, and Achilles’ tendon elongation, strain, and stiffness. Netballers displayed significantly higher absolute tendon thickness (p = 0.004 for Achilles’, p = 0.021 for patellar), but not when normalised to body mass. Netballers also displayed significantly higher Achilles’ tendon stiffness (p = 0.046) and isometric plantar flexion and knee extension strength (both p < 0.001). No differences were detected in any other measure of muscle or tendon morphology. The results of this study provide evidence that power modulation activities promote different muscle-tendon unit properties to energy conservation activities in females, but that these adaptations may be body mass dependent.