Effects of body condition on metabolism, performance and recovery

Background

There is a perception in the world of sports that an increased amount of body fat reduces performance in many sports, even among elite athletes who do not normally have much extra fat. However, there are few studies that have investigated whether and why this is the case under controlled conditions. The question of how body fat content affects performance is also relevant in equestrian sports. There are a few studies that have compared the performance of individuals or groups of horses with different body fat content, and in most cases it has been observed that horses with better performance, even at the elite level, also have a lower body fat content. However, these types of studies cannot provide answers about cause and effect. Perhaps it is simply that individuals who have trained a little more (and therefore also become better) have also consumed more fat?

About this study

We have conducted a controlled study in which we investigated what happens to performance and the physiological and metabolic response during work in a group of horses if they both increased and decreased in body fat content. This type of study design provides a better understanding of what may be behind a change in performance, as it does not compare different individuals but rather the same individual with itself, in this case, the performance of the same individual with different body fat content.

Nine horses (weighing approximately 400 kg) were studied over two periods of 36 days, one of which involved them receiving slightly more feed (energy) than they needed, resulting in an increase in weight (and body fat). The second period involved them receiving the energy they needed or slightly less, which meant that they lost a little weight or maintained their weight. The difference in weight between the two periods was 15-20 kg and the difference in body fat content and condition was 5-8%. At the end of each period, the horses underwent two types of work tests and various physiological and metabolic measurements were taken.

Results

When the horses had higher body fat content, their heart rate increased during standardized work and their lactate threshold decreased. Both of these effects were expected and may be a direct result of the horses becoming heavier. Both effects are linked to reduced performance. A less expected effect was that they also had lower blood glucose levels, which is also unfavorable for performance. Another unexpected effect was that the proportion of red blood cells decreased as body fat content increased, which may also be linked to reduced performance. The reason for this is unclear, but it may be because the liver (which takes care of old red blood cells) functions differently at higher body fat content. It also took longer for the horses to reduce their lactic acid concentration after work when they had higher body fat content.

When assessing the quality of the horses' gaits, their lightness, and willingness to work (in a competition-like riding test), the horses also received lower scores when they had higher body fat content. This was assessed by judges who were unaware of the horses' body fat content (a blind study). The impact on movement patterns was also confirmed by objective movement analysis (sensor-based analyses) where the horses, without riders, moved more asymmetrically when they had higher body fat content. Overall, this study shows that increased body weight and body fat content cause a physiological and metabolic response that is not good for performance. The condition also delays recovery after work and appears to have a negative effect on movement patterns.

Link to the full study

Increased body fat content in horses alters metabolic and physiological exercise response, decreases performance, and increases locomotion asymmetry - Jansson - 2021 - Physiological Reports - Wiley Online Library