MUSCLE FATIGUE – Training and nutrition
Updated: Sep 2
There are different definitions of Fatigue, but in sports it is defined as the inability to maintain the required or expected strength. Another definition that is used in exercise physiology is that fatigue occurs when the regeneration rate of adenosine triphosphate (ATP) is not equal to the utilization rate. If you don’t know what ATP is, imagine it as a source of energy. Although this is a somewhat enlightening definition, today we know that in some cases fatigue can arise even if there is a satisfactory ATP regeneration rate. Muscle fatigue implies that the athlete is no longer able to sustain a certain level of performance, whether in activities such as weight lifting or in aerobic activities such as running or cycling.
Fatigue is not caused by an accumulation of lactic acid as many mistakenly think, but by the interruption of the chain events that occur between the central nervous system and the muscle fibers. To better understand these processes, I refer you to the video about Neuromuscular Training.
The interruption of these chain of events is manifested by the decrease in the production of force and the slowing down of muscle contraction. Going back to lactic acid, I said that its accumulation is not the cause of fatigue, but this does not mean that it does not play a role in the process of interrupting the chain of events. Indeed, an accumulation of lactic acid in the muscles can reduce the activity of the enzymes involved in metabolism and consequently reduce the availability of energy. It can also interfere with chemical processes by slowing down muscle contraction. To learn more about lactic acid, I leave you the link to a video by Gian Mario Migliaccio.
How does fatigue manifest itself? There is a bit of confusion on this point, where fatigue and DOMS are often confused. Let’s start by saying that they are not the same. DOMS (Delay-Onset Muscle Soreness) are muscle pains that arise between 24 and 48 hours after training as a result of small lesions of the muscle fibers to which the body reacts by increasing the state of inflammation which then leads to perceive these pains with delayed burst. The symptoms of fatigue, on the other hand, arise during physical activity and manifest themselves as: • Acidosis: muscle burning sensation • Loss of strength: inability to handle the same load • Loss of speed: inability to maintain a high speed of movement
Is it bad to feel fatigue? Of course not, if you want to get the most out of your training. The Powerlifting champion and researcher, Dr. Claire Minshull, explains it with an example based on PowerLifting. She says, “If you want to train to get stronger, your training should be structured like this: – 3-5 RM. A load with which you do only 5 repetitions, with which if you try to do the sixth you will not be able to perform it correctly. – 2 minutes of rest between sets – 3-5 sets per exercise
Why following this protocol? The muscle fibers we use during strength training (fast fibers) are strong by nature, but have a limited source of energy. They tire quickly, so strength exercises should consist of 3-5RM and adequate rest time between sets so that they can recover and you can get the most out of each set. How can we prevent fatigue? Guidelines for preventing chronic fatigue in athletes were drafted in a 1991 study. With intense and repeated training the carbohydrate reserves are emptied and it takes at least one or two days of rest or light activity and carbohydrate intake to restore muscle glycogen reserves. The guidelines provide for: • Consume easily digestible foods/drinks with a high carbohydrate content or solid foods 1 to 4 hours before training or competition, staying in a range of 1-4 g of carbohydrates/kg. • Consume fast digestible foods, liquid or solid, containing from 0.35 to 1.5g of carbohydrates per/kg of body mass immediately after exercise or in any case within the following 4 hours. • Consume a drink or solid food containing between 15 and 25% carbohydrates as a supplement to each meal. • Try to maintain a stable weight during the training phases by evaluating the energy consumption and energy demand of the training itself so as to maintain glycogen reserves.
References Edwards, R. H. T. (1981) ‘Human muscle function and fatigue.’
Hultman, E. e Sjoholm, H. (1986) ‘Biomechanical causes of fatigue.’ McArdle, W. D. et al. (2014) ‘Exercise Physiology: Nutrition, Energy and Human Performance.’ Minshull, C. (2016) ‘What is fatigue ? – The basics and how it impacts your training.’ Sherman, W. J. e Maglischo, E. W. (1991) ‘Minimizing chronic athletic fatigue among swimmers: special emphasis on nutrition.’