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Title: The effect of reproductive hormones and energy availability on muscle function, cognition and bone metabolism in females
Author: Martin, Dan
Awarding Body: Nottingham Trent University
Current Institution: Nottingham Trent University
Date of Award: 2018
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The Relative Energy Deficiency in Sport (RED-S) model has proposed that several health and performance factors, including muscle strength and elements of cognitive function, are affected by reduced energy availability (EA) in athletes, yet there is currently limited evidence available to support this. Furthermore, it is not known whether alterations to reproductive hormones, that occur with low EA, impact these factors in the same way that bone metabolism is synergistically affected by hypothalamic amenorrhea and low EA in the Female Athlete Triad. Any potential effects of reproductive hormones are further confounded by hormonal contraceptive (HC) use, which down-regulates reproductive hormones, while supplying exogenous reproductive hormones to the system, although the prevalence of HC use in female athletes is not known. In Chapter 4, it was shown that quadriceps and first dorsal interosseus (FDI) muscle force measurements were reliable (ICC = 0.990-002, CV = 3.21-3.22 %) and suitable for use in subsequent chapters (Chapters 6 and 9). In Chapter 5, it was shown that approximately half (49.5%) of 430 elite female athletes used HCs, with 50.5% using no form of HC, evidencing the importance of considering both HC users and non-users in future research. The majority (69.8%) of HC use was comprised of combined oral contraceptives (OCs) and the main reason for using these preparations was the perceived ability to manipulate menstruation. In Chapters 6-8, muscle force production (quadriceps force, FDI muscle force and countermovement jump height), cognitive function (verbal memory, spatial awareness, verbal fluency, psychomotor performance, executive inhibition and attention) and bone metabolism (Carboxy-terminal cross-linking telopeptide of type 1 collagen [β-CTX], Procollagen Type 1 N Propeptide [P1NP] and bone-specific alkaline phosphatase [BAP]) were assessed across the menstrual cycle (early follicular [EF], ovulatory [OV] and mid-luteal [ML] phases; n= 14) and OC cycle (early pill consumption [PC1], late pill consumption [PC2] and pill-free interval [PFI]; n=14). Muscle force production, cognitive function and bone formation (P1NP, BAP) were not affected by menstrual cycle or OC phase (main effect time; all P > 0.05). This was despite significant variations in oestrogen concentrations between menstrual cycle phases (main effect time; P < 0.05) and measuring during the pill-free interval (PFI) and early and late pill consumption in OC users. Bone resorption marker (β-CTX) concentrations, however, were significantly higher (+16.0%; P = 0.014; d = 0.37) during PC1 compared to PC2, showing the importance of exogenous hormones in regulating bone metabolism. In Chapters 9-10, 20 participants (10 eumenorrheic, 10 OC users) completed three, 3-day conditions: controlled-balanced EA without exercise (BAL; 45 kcal·kg·LBM-1·day-1), diet-induced low EA without exercise (DIET; 15 kcal·kg·LBM-1·day-1) and exercise-induced low EA (EX; 15 kcal·kg·LBM-1·day-1, including 30 kcal·kg·LBM-1·day-1 treadmill running at 70% V̇O2max). Muscle force ( quadriceps and FDI muscle) and cognitive function ( verbal memory, spatial awareness, psychomotor performance, executive inhibition and attention) were measured before and after each condition. DIET had no effect on muscle force production or cognitive function, while EX significantly impaired quadriceps force production (-13.2%; P < 0.05) and mental rotation accuracy (-1.4%; P < 0.05). The muscle and cognitive response to low EA were not different between eumenorrheic women and OC users (all P > 0.05). In conclusion, changes to the reproductive hormone environment that occur with low EA are not as important a consideration for muscle function and cognitive function compared to bone metabolism. Furthermore, short-term low EA achieved via dietary restriction does not affect muscle force production or cognitive function, but exercise-induced low EA impairs muscle force production and aspects of cognition, evidencing the importance of considering the method by which low energy is achieved in the RED-S model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available