Active Voice: Train High or Low with Carbohydrate? Best Strategies for Improving Sports Performance
By Louise Burke, Ph.D., FACSM, FSMA

Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.

Louise Burke, Ph.D., FACSM, FSMA, is Head of Sports Nutrition at the Australian Institute of Sport in Canberra, Australia. Dr. Burke manages a department providing clinical counseling and education of athletes, research, student supervision and teaching, and development of education resources, and she also oversees food services for athletes. Dr. Burke is a member of the Nutritional Working Group for the International Olympic Committee and the Medical and Anti-Doping Commission for the International Association of Athletics Federations. Her research focus relates primarily to the effects of specific nutrient interventions on metabolism and exercise performance in athletes.

Traditionally, athletes have approached their daily workouts to train as hard as possible, using strategies that promote good performance, just as they would in a race or match. In many sports, these strategies involve fueling up with carbohydrates before, during and between workouts to sustain the capacity to produce power. Recently, however, scientists have proposed an alternative approach – training smarter by trying for greater outcomes from the same training impulse. The muscles’ reactions have shown that when a muscle is low in carbohydrate fuel, there is an increased chemical response to a training stimulus. One study by Bengt Saltin’s group in Denmark compared what happened when untrained people completed ten weeks of training with one leg training low (TL) and the other leg training high (TH). Although each leg completed the same training sessions, the TL leg beat out the TH leg in terms of the muscle’s changes and its capacity to exercise until fatigued. While some publicity surrounding this study suggests otherwise, the outcomes from TL weren’t achieved by following a low carbohydrate diet. Rather, this was accomplished by doing two sessions of exercise back-to-back so the muscle had no time to refuel before the second session. Only half of the training was done with low muscle fuel stores.

Other studies have found that exercising while fasted (a pre-breakfast workout completed on water) was better at changing the chemistry of the muscle than training while consuming carbohydrate. No differences in performance gains were seen this time. While these studies offer intriguing results, particularly to speed up the health benefits of exercise for sedentary people, the benefits for the elite and well-trained athlete focused on performance results is an area of debate. Follow-up studies using TL strategies in well-trained athletes have not found any performance benefits over TH, although the muscle chemistry adaptation in the TL condition has often shown superior gains. Importantly, TL strategies have interrupted the capacity of athletes to train at high speeds or high power outputs.

This situation is similar to the evolution of altitude training techniques. Where early studies promoted this specialized technique because of its ability to increase the positive gains of training, athletes and coaches later realized the downside of being unable to do key training sessions at the desired high workloads. Athletes have since resolved the issue by mixing altitude training into their periodized training calendar, so they have short-term exposure during their baseline phases or so they can arrange to do their high-intensity sessions at sea level without interference. This approach might offer some clues of how to get the best from the potential benefits of TL with carbohydrates.

In fact, sports dietitians often observe that athletes already periodize their nutrition for training. Whether it’s by accident or design, some training sessions are already completed with low carbohydrate status (e.g. first thing in the morning or the second session of the day). In contrast, other sessions are already completed using strategies that promote carbohydrate status (e.g. allowing more recovery time, sessions done after breakfast or a meal, or workouts in which carbohydrate is consumed).

So should athletes deliberately add more TL sessions to their training routine? More studies are needed to see if this will actually lead to better performance or a quicker time to reach better performances (read more). In the meantime, other potential negatives include an increased risk of illness or injury and the loss of some newly recognized benefits from TH. In one recent study, we found that cyclists who consumed carbohydrate drinks during their training sessions increased their ability to absorb and use carbohydrate as an exercise fuel. Athletes may like to experiment to find the best mix of TH and TL in their own programs. It makes sense that sessions completed at lower intensity or at the beginning of a training cycle are best suited for, or perhaps least disadvantaged by, TL strategies. Conversely, quality sessions done at higher intensities or in the transition to peaking for competition might best be undertaken with better fuel support. As with many aspects of training, solutions will need to be individualized to each athlete and his or her goals.