Investigating the effects of acute photobiomodulation on submaximal rowing performance and physiological responses in trained female rowers

Abstract

It is well established that Red Light Therapy (RLT), or Photobiomodulation (PBM), can enhance mitochondrial function, reduce markers of muscle damage, and improve exercise performance and recovery. As a result, RLT has become an increasingly popular non-invasive intervention within sport and exercise settings. Recent research has shown that pre-exercise application of red and near-infrared light may improve time to exhaustion, reduce fatigue, and enhance recovery in activities such as cycling, running, and resistance exercise. However, there is currently no research examining the effects of RLT on rowing performance, particularly during submaximal exercise in trained female rowers.

This thesis is separated into three chapters. Chapter one provides a review of the literature on RLT, beginning with its historical development and underlying physiological mechanisms of action. This review includes a discussion of the interaction between RLT and mitochondrial chromophores, effects on adenosine triphosphate (ATP) production, oxidative stress modulation, and nitric oxide-mediated processes. The chapter further examines the role of RLT in exercise performance and recovery, with particular emphasis on muscle fatigue, endurance capacity, and post-exercise recovery markers.

The literature review also critically evaluates the application of RLT across a range of exercise modalities, including resistance exercise, cycling, and running, while highlighting the variability in outcomes reported across studies. Particular attention is given to inconsistencies in methodological approaches, including differences in wavelength, dosage, timing of application (pre- versus post-exercise), and participant characteristics. Chapter One also identifies key gaps in the current literature, notably the limited research in endurance -based, sport-specific contexts and the underrepresentation of female athletes. These gaps provide the rationale for the present study, with a specific focus on rowing as an endurance sport requiring sustained submaximal performance and efficient recovery. Rowing has continuous physiological demands on both the upper and lower body and relies heavily on sustained submaximal power output and efficient recovery between repeated efforts.

As a result, Chapter Two investigated the acute effects of PBM on submaximal rowing performance and exercise physiology in trained female athletes. Twelve trained female rowers participated in a placebo-controlled, double-blind, randomized crossover design. Each participant completed five laboratory sessions, beginning with a maximal graded exercise test to determine maximal oxygen uptake (VO2max) and establish individualised workload targets for subsequent submaximal trials. The remaining four sessions involved identical rowing protocols performed following one of four treatment conditions: red light (630 and 660 nm), near infrared (810, 830 and 850 nm), combined red and near-infrared light, or placebo condition. Treatment order was randomised, and participants were blinded to the condition. A minimum of 48 hours recovery was maintained between sessions to minimise potential carryover effects. Primary outcome measures included oxygen uptake (VO2), blood lactate concentration, and blood glucose concentration during progressive submaximal exercise. Secondary measures included respiratory exchange ratio (RER) and ratings of perceived exertion (RPE), providing a comprehensive assessment of both physiological and perceptual responses to PBM.

Statistical analysis revealed participants completed a greater number of submaximal rowing intervals following the red light (7.25 ± 0.75 intervals; p = 0.046) and infra-red light (7.25 ± 0.45 intervals; p = 0.012) conditions compared with the placebo condition (6.67 ± 0.98 intervals) indicating improved exercise capacity. PBM was also associated with lower blood glucose concentrations during the exercise intensity closest to the lactate threshold in the infra-red condition (p=0.0300; d= 0.58 ±0.51). There were also differences in RER responses between the red light and placebo conditions suggesting alterations in energy utilisation during exercise. However, no significant differences were observed in VO2, blood lactate concentration, or RPE between conditions. These findings suggest that pre-exercise PBM may enhance submaximal rowing performance through alterations in metabolic responses, including utilisation and glucose regulation, while producing only limited changes in broader physiological responses.

Chapter Three summarises the findings from Chapter Two, identifies the strengths and limitations for the present study, and provides recommendations for future research. Overall, this thesis identified key gaps within the existing literature on PBM (RLT), particularly in relation to sport-specific endurance performance, female athlete populations and submaximal exercise protocols.