The experience of feeling tired after a workout is normal and affects all exercisers. When you feel absolutely exhausted after an exercise session, however, you may be concerned that you are pushing yourself too hard. Exhaustion is also normal, assuming you're not overexerting yourself. Through defining exhaustion, and finding its source and factors, you can develop an appropriate strategy to fight this feeling.
You can see exhaustion as a physical state or a mental state, depending on your viewpoint. Defining exhaustion is a complex task, and a number of models claim to explain exhaustion. You can divide the models of exhaustion into two groups: mental models and physical models. In a mental model, psychologists explain how the drive for exercise can be reduced, leading to a feeling of lack of motivation, or exhaustion. In a physical model, physiologists explain how the body engages in mechanical force until it has problems continuing to supply the energy needed for this force. In either case, an assumption that exercise is being done for a period of time implies that energy supply and depletion is a major reason for any model of exhaustion.
The main reason your body gets to this exhausted state is that exercise requires you to move your muscles so force is created. This force comes from muscle contractions, which require energy in a chemical form. Your body runs on a duo of chemicals by the names adenosine triphosphate (ATP) and glycogen. The chemical ATP is in every cell in your body and is the main player in supplying energy during exercise. Glycogen is in storage areas, mainly your muscles and liver. Exhaustion occurs when your body cannot gather the supply of ATP and glycogen it needs. The experience of exhaustion is your body telling you that the ratio of energy supply to energy need has become restrictively low.
Factors that affect how quickly you will become exhausted and how exhausted you will be after a workout are numerous. The main factors determining your level of exhaustion include your age, the intensity of the exercise and the length of the workout. Your age influences how much energy your body can store, with reserves decreasing as you get older. The intensity of the workout shifts how you use energy, with more intense workouts drawing more glycogen and less intense workouts drawing from fat reserves; you will feel more exhausted after an intense workout, as it is glycogen depletion that makes you feel tired. The length of the workout determines how long your body will be drawing increased rations from its energy stores; a longer workout will deplete more energy.
Numerous strategies that address the scientific reason for exhaustion exist. One of the easiest ways to fight exhaustion is to resupply your body with energy. The two main ways of doing this are ingesting carbohydrates and resting. Eating a meal high in carbohydrates can help postpone the feeling of exhaustion during a workout. Resting can involve short breaks in between workout sessions or weightlifting sets; it can also involve long breaks, over the course of days. If you feel exhausted after a weightlifting session, resting for long periods of time is a better option, as your muscles will need a few days to recover.
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