Nutrition factors associated with rib stress injury in elite rowers

Rib stress injuries (RSI) contribute the highest loss of training time of all rowing related injuries, negatively affecting training consistency and the ability to produce optimal performances when needed. Nutrition interacts with training to moderate bone growth, repair and maintenance and, as such, is of interest in understanding changeable contributors to injury.

Given the scarcity of available research, this thesis investigated nutrition factors associated with RSI, the development of a tool to assess one of these factors, low energy availability (LEA), and the effects of acute calcium intake on markers of bone turnover (BTM) over a typical training day.

Study 1 (Chapter 4) was a cross-sectional analysis of RSI history and related nutrition factors in elite Australian rowers (n= 133). Bone mineral density (BMD), body composition, vitamin D and K status, usual calcium intake, menstrual history, diet restriction, age, sex, training age and injury history were assessed.

Diet restriction was inversely related to spine and rib BMD. Vitamin D and K status, and calcium intake were not associated with injury. Among rowers with RSI history, lightweight males had lower total bone mass, femur and rib BMD, whereas heavyweight females had lower rib BMD. In relation to RSI history, the best models included rib, spine or femur BMD with age, body fat and sex. A female specific
model included current menstrual dysfunction, age and body fat levels.

Study 2 (Chapter 6) aimed to develop and validate a screening tool for low energy availability (LEA) in male athletes. This was a multi-centre collaboration, recruiting male athletes (n=310) from a variety of sports. Multivariate analysis was used to identify associations between variable responses
and clinical markers, and Receiver Operating Characteristics (ROC) curve analysis of variables, with an inclusion threshold of 60% sensitivity. Of the variables, dizziness, illness, fatigue, and sex drive had sufficient sensitivity to be retained in the questionnaire, but only low sex drive was able to distinguish between LEA cases and controls. In this large and international cohort, low sex drive was the most effective self-reported symptom in identifying male athletes requiring further clinical assessment for LEA.

Study 3 (Chapter 8) examined the influence of acute calcium intake on bone turnover markers over a typical training day in elite male rowers. While acute exercise typically increases BTM, the impact of subsequent sessions and the interaction with pre-exercise calcium intake remains unclear despite the application to the ‘real life’ training of athletes. Using a randomized crossover design, elite male rowers (n=16) completed two trials, a week apart, consisting of two 90-minute rowing ergometer sessions (Ex1, Ex2) separated by 150min. Prior to each trial, participants consumed a high (CAL: ~1000 mg) or isocaloric low (CON: <10 mg) calcium meal. BTM (parathyroid hormone: PTH; C-terminal telopeptide of type I collagen: β-CTX-I; osteocalcin: OC) and serum ionised calcium (iCa) were monitored from baseline to 3 hours post Ex2.

While each session caused perturbances of serum iCa, CAL maintained calcium concentrations above those of CON for most time points, 4.5 and 2.4% higher post EX1 and EX2 respectively. The decrease in iCa in CON was associated with an elevation of blood PTH and β-CTX-I over this period of repeated training sessions and their recovery, particularly during and after Ex2. Pre-exercise intake of a calcium-rich meal prior to training sessions undertaken within the same day had a cumulative and prolonged effect on the stabilisation of blood iCa during exercise. In turn, this
reduced the post-exercise PTH response, potentially attenuating the increase in markers of bone resorption.

Collectively the findings of the thesis were
1. Clarification of associations between nutrition factors and RSI history informing future monitoring and interventions, LEA is important.
2. Association of rib BMD with RSI providing practical benefits to frequency of monitoring and lower radiation dose, opening avenues for better characterisation of its relationship with RSI.
3. Sex drive is an important indicator of LEA in male athletic populations
4. Pre-exercise calcium has the potential to safeguard long term bone health and reduce the risk of bone stress injuries and is a practical strategy, easily integrated into the athlete’s overall sports nutrition plan, complementing those adequacy of EA.