At the cellular level, muscles rely on efficient energy production for contraction and function. With exercise intolerance, there can be a problem with the metabolic pathways, specifically in the mitochondria, which are the energy powerhouses of the cell. This can result in decreased ATP production, the primary energy currency for muscle contraction. The outcome? Muscle weakness and premature fatigue even with minimal exertion.
Lactic acid build-up is another concern. During strenuous exercise, lactic acid accumulates in the muscles, leading to the familiar sensation of muscle burn. However, in individuals with exercise intolerance, this accumulation can occur much more rapidly and at lower intensities of activity, causing pain and cramping far earlier than it would in a healthy individual, per a 2012 study in Neuromuscular Disorders.
Furthermore, muscle recovery post-exercise is often compromised. Inefficient removal of metabolic waste products and reduced blood flow can prolong muscle soreness and delay the healing process (via Physio.co.uk). This persistent muscle discomfort is not just the typical post-workout ache but an extended period of pain and sensitivity.
Lastly, the chronic nature of these muscular effects can lead to muscle atrophy over time. The combination of reduced activity due to pain and fatigue, along with potential metabolic deficiencies, can result in muscle wasting, further exacerbating weakness and reducing endurance, per a 1992 study in Circulation.