What limits endurance exercise performance?

As an Australian, one of the most memorable moments of the 2004 Summer Olympic Games was the final of the women’s eights rowing (www.youtube.com/watch?v=ZK529UiaFZQ). The Australian team, by no means the favourites, were well-positioned for a podium finish at the half-way point of the 2000-m race. Soon after the half-way mark they slipped out of 3^rd place and gradually began to fade. The Australian’s finished the race in last place with a time 6:31.65, nearly 10 seconds behind the rest of the field, which was otherwise separated by just over 4 seconds. Why would such a race be so memorable for me? Because the large gap between Australia and the rest of the field was primarily caused by one rower, Sally Robins, who with approximately 500 m to go lay down and stopped rowing! She had clearly reached the point of exhaustion.

For over a century sports scientists have attempted to identify the factor/s guilty of causing exhaustion and limiting endurance exercise performance. The blame has traditionally been placed (either individually or in combination) on factors such as ‘lactic acid’ accumulation, high core temperature, depleted energy stores and inadequate delivery of oxygen to the muscles [1].  But when asked about the incident in the 2004 Olympics, Sally Robins didn’t blame any of these factors. She simply stated that she “didn’t have anything left”. Is it possible that Sally Robins and other endurance athletes are limited by psychological constructs rather than physiological mechanisms?

This may indeed be the case, with large amounts of contemporary research on fatigue and endurance performance emphasizing the importance of the brain. In recent years, this trend toward emphasizing the brain began with the development of the Central Governor Model [2]. In short this model proposes that a subconscious centre within the brain regulates exercise performance based on physiological feedback from the body, with the main purpose of maintaining homeostasis and avoiding exercise-induced damage. Therefore we stop exercising or slow down because the ‘central governor’ perceives continuation to be dangerous.

An alternative and less complex theory also exists. Based on Brehm’s motivational intensity theory, the Psychobiological Model suggests that endurance performance is determined by two main psychological factors in the conscious brain: motivation and perception of effort [3, 4]. Put simply, during endurance exercise we stop/slow down because we have either i) exerted the maximum effort we are willing to exert for success (i.e. lack of motivation limits us) or ii) we believe we have exerted our maximal possible effort and we simply cannot continue at the current pace (i.e. our perception of effort limits us). Therefore, assuming that Sally Robins was highly motivated (she was in an Olympic final!), the Psychobiological Model of endurance performance would agree with her statement that she “didn’t have anything left”, attributing her ‘exhaustion’ to a maximal perception of effort.

It seems too simple doesn’t it? Well the evidence suggests otherwise. In fact in a study published in the European Journal of Applied Physiology in 2010 [5], athletes were asked to cycle until exhaustion at 80% of their peak power (~240 W). On average they lasted 10.5 minutes before their perception of effort was maximal and they could no longer cycle at the required 240 W. Immediately after this point of ‘exhaustion’, without any prior knowledge, the athletes were asked to produce a maximal effort for 5 seconds. This is where the important results occurred – the athletes were able to reach a cycling power output of 730 W. That’s three times higher than the power they were required to generate to continue in the test to exhaustion. Therefore, the authors concluded that although the athletes were clearly able to physically generate the required power, they stopped cycling because they perceived their effort to be maximal.

So, if as the evidence suggests, the Psychobiological model is correct, the key to improving endurance performance lies in increasing motivation, decreasing perception of effort or a combination of both. We don’t have room to go into detail here about how to do that but you can check out some other TheSportInMind posts for ideas on how to increase motivation. As for decreasing perception of effort; evidence suggests that both caffeine [6] and self-talk [7] can significantly reduce perception of effort and increase endurance performance. Or you could always just train more!