To eat or not to eat? That is the question – The physiology behind a boxer’s fasted cardio.
A staple in a boxer’s training regime is the morning fasted cardio session. This could be in the form of a low intensity steady state run or a light pad work circuit.
It is well known that carbohydrates are king when it comes to fuelling exercise performance and athletes are encouraged to take on carbohydrates before, during and after exercise to enhance their energy levels and performance. So why do boxers perform fasted cardio so regularly?
Carbohydrates are converted into glycogen when consumed. Glycogen is stored in the liver and the muscles as a fuel source (1). These stores become depleted during exercise as they are used by the muscles for energy. Stores must be replenished by consuming carbohydrates following exercise.
Similarly, after an overnight fast, glycogen stores become depleted during sleep. If no breakfast is consumed, boxers will begin their cardio session with low glycogen stores. As glycogen stores are low, the body will utilise other fuel stores as a substrate to provide energy for the working muscles. The next fuel source the body will look to break down into energy is fat. Therefore, you may hear fasted sessions being referred to as ‘fat burning’ sessions.
However, this does not mean body fat is being eaten away during fasted exercise. It simply means fat is being used as the primary fuel for metabolism and if the goal is weight loss, an energy deficit is required.
A boxer will participate in fasted cardio for performance adaptations. Recent studies have suggested that training with reduced glycogen availability can enhance aerobic performance (2). There is evidence to suggest training in a fasted state may translate into increases in mitochondrial number and volume, leading to enhanced aerobic performance (3). Although, more research is required in this area.
Performing in a fasted state regularly means boxers will adapt to be able to perform comfortably when using fat as the primary substrate for metabolism. This will mean the boxer is better adapted and comfortable when using fat for fuel in later rounds when their glycogen stores have become depleted. Which can lead to strong performances and late round knock outs.
Sam Keane, BSc (Hons), MSc, (SENr)
@SamKeaneMethod
References
(1) Burke, L., Hawley, J., Wong, S and Jeukendrup, A. (2011). Carbohydrates and training for competition. Journal of Sport Sciences. 29 (Supp 1), S17 – S27.
(2) Impey, S., Hearris, M., Hammond, K., Bartlett, J., Louis, J., Close, G and Morton, J. (2018). Fuel for the work required: A theoretical framework for carbohydrate periodisation and the glycogen threshold hypothesis. Sports Medicine. 48, pp: 1031-1048.
(3) Van Proeyen, K., Szlufcik, K., Nielens, H., Ramaekers, M., Hespel, P. (2011). ‘Beneficial metabolic adaptations due to endurance exercise training in the fasted state’. Journal of Applied Physiology. 110, pp: 236–45
