Neuromuscular fatigue is an inevitable consequence of sustained physical activity. When you make the conscious decision to move, many processes in the central nervous system work together to supply activation signals to your muscles. There are also a number of responses within the muscles that are needed to put this movement plan into action. Neuromuscular fatigue occurs when any of these mechanisms becomes taxed.
The effects of neuromuscular fatigue are different, depending upon the physical tasks you are performing. During very strenuous exercise, neuromuscular fatigue necessitates a reduction in work rate, whereas during less demanding efforts, the same work rate can be maintained with an increased perception of difficulty. In the latter case, body systems must work harder to accomplish the same rate of work, which is particularly problematic for the cardiovascular system because the heart will be activated to higher levels. This will cause a greater blood pressure response, higher heart rate and increased demand for oxygen by cardiac tissue.
Central and Peripheral Fatigue
Neuromuscular fatigue can have both central and peripheral elements. As explained by S.C. Gandevia in the October 2001 issue of "Physiological Reviews," there is controversy regarding the degree to which each of these contributes to the fatigued state. Peripheral aspects are those that occur in the muscles performing the task. These processes are easier to assess, which is why they have received most of the attention in the literature. However, a growing body of research suggests that in some cases, at least part of the loss of performance due to fatigue may be attributable to central mechanisms. These include anything that can interfere with the brain's ability to signal for the appropriate muscular response.
Regardless of whether it originates from central or peripheral locations, the degree of neuromuscular fatigue you experience when performing a physical task depends upon the relative difficulty of the task. When muscles are not regularly challenged by demanding physical endeavors, the neuromuscular system becomes less capable, and the relative difficulty associated with every physical task you perform will increase. This means that even typical physical activities of daily living might produce significant neuromuscular fatigue. The goal of exercise training is to systematically overload your neuromuscular system to force it to adapt to higher levels of development. The end result is that the neuromuscular fatigue you experience during the exercise session conditions your body such that the other physical activities you perform in your life will be far less stressful.
Progressive Resistance Exercise
The positive changes you can expect from an exercise program are highly specific to the type of exercise you perform. To challenge neuromuscular function and force it to improve, your muscles must work against loads that they can only move for short periods of time. Progressive resistance exercise with free weights or machines provides this stimulus, and a weight that you can lift and lower for no more than 90 seconds before having to rest is the appropriate resistance for this type of training. The progressive nature reflects the fact that the right load now is not the one you should be using in the future, because once your system adapts a greater load will be required to elicit the same stimulation. The Physical Activity & Public Health Guidelines from the American College of Sports Medicine and the American Heart Association state that healthy individuals should perform progressive resistance exercise for all of the major muscles of the body two times each week.
To decrease neuromuscular fatigue and associated cardiovascular stress during all of your daily physical activities, you have to experience it on a regular basis during progressive resistance exercise sessions. This means that it is unavoidable that such sessions will stress your cardiovascular system. For this reason, you should consult your physician before beginning a progressive resistance exercise program.