Journal Title (Medline/Pubmed accepted abbreviation): Br J Sports Med
Page number: 2
Article type: Commissioned editorial
This brief editorial (1 page) discusses the current evidence for recommendations on fluid replacement during exercise. Several current and 1 older study casting doubt on the benefit of aggressive fluid replacement on competitive sports performance are presented, specifically the report by Marino et al ( Br J Sports Med.
2010; 44:961-967) challenging the belief that (full) fluid replacement is necessary during high-intensity exercise. This study evaluated neuromuscular changes during exercise with hydration status and its effect on several parameters, including peak and terminal core body temperature, heart rate, and performance. These analyses demonstrated no reduction in cycling performance at 33°C without hydration (despite a body mass loss of 2.1%) compared with 20°C when fully hydrated. In addition, a study by Robinson et al (Eur J Appl Physiol. 1995;71:153-160) observed similar findings for cycling performance among hydrated and non-hydrated subjects (2.2% body mass loss), although fully hydrated subjects had decreased performance.
The author raises the question, “Why does the sports medicine community still encourage drinking to improve performance?” when several studies offer contradictory evidence. Studies have shown that prolonged exercise has been linked to dehydration, which is in turn linked to reduction in plasma volume, cardiac stroke volume and output, osmolality, mean arterial pressure, body temperature, and increased perception of effort and exercise duration. Also, fluid replacement can attenuate the effects that are exacerbated by heat stress. However, the author disputes that previous studies adequately evaluated the effect of (full) fluid replacement on mitigating these adverse consequences.
These observations are based on an experimental model of exercise that primarily measures fixed-intensity exercise. This approach has been reasonable for concluding that an independent variable, such as fluid intake, has an effect on a dependent variable like exercise performance. This approach may not be as relevant when evaluating exercise performance as it occurs in real life (ie, where speed may outweigh endurance). Typically, fixed-intensity exercise measures performance based on volitional fatigue, or the athlete’s decision to continue or stop exercise, ad libitum. “Real-life” competition is more accurately modeled with a race to complete a set distance where self-paced exercise performance measures allow continual adjustments to pace or workload, as needed, to maximize performance.
Several studies are described refuting the commonly held belief that maximum fluid replacement enhances exercise performance. It is the position of the author of this editorial that the literature should be reevaluated in light of the evolution of performance testing favoring a more realistic self-paced exercise model over the traditional fixed-intensity model.