Question

Thirty-five-year-old Jane recently began "working out" and jogs three times a week. After her jog, she is breathless and her muscles ache.

From your understanding of muscle physiology, describe what has happened inside Maggie's skeletal muscle cells. How do her muscle cells recover from this?

Answer 1

As our bodies perform strenuous exercise, we begin to breathe faster as we attempt to shuttle more oxygen to our working muscles. The body prefers to generate most of its energy using aerobic methods, meaning with oxygen. Some circumstances, however—such as evading the historical saber tooth tiger or lifting heavy weights—require energy production faster than our bodies can adequately deliver oxygen. In those cases, the working muscles generate energy anaerobically. This energy comes from glucose through a process called glycolysis, in which glucose is broken down or metabolized into a substance called pyruvate through a series of steps. When the body has plenty of oxygen, pyruvate is shuttled to an aerobic pathway to be further broken down for more energy. But when oxygen is limited, the body temporarily converts pyruvate into a substance called lactate, which allows glucose breakdown—and thus energy production—to continue. The working muscle cells can continue this type of anaerobic energy production at high rates for one to three minutes, during which time lactate can accumulate to high levels.

A side effect of high lactate levels is an increase in the acidity of the muscle cells, along with disruptions of other metabolites. The same metabolic pathways that permit the breakdown of glucose to energy perform poorly in this acidic environment. On the surface, it seems counterproductive that a working muscle would produce something that would slow its capacity for more work. In reality, this is a natural defense mechanism for the body; it prevents permanent damage during extreme exertion by slowing the key systems needed to maintain muscle contraction. Once the body slows down, oxygen becomes available and lactate reverts back to pyruvate, allowing continued aerobic metabolism and energy for the body’s recovery from the strenuous event.

Contrary to popular opinion, lactate or, as it is often called, lactic acid buildup is not responsible for the muscle soreness felt in the days following strenuous exercise. Rather, the production of lactate and other metabolites during extreme exertion results in the burning sensation often felt in active muscles, though which exact metabolites are involved remains unclear. This often painful sensation also gets us to stop overworking the body, thus forcing a recovery period in which the body clears the lactate and other metabolites.

Researchers once attributed fatigue to a build-up of lactic acid in muscles.However, this is no longer believed. Rather, lactate may stop muscle fatigue by keeping muscles fully responding to nerve signals.The available oxygen and energy supply, and disturbances of muscle ion homeostasis are the main factor determining exercise performance, at least during brief very intense exercise.
Each muscle contraction involves an action potential that activates voltage sensors, and so releases Ca²⁺ ions from the muscle fibre’s sarcoplasmic reticulum. The action potentials that cause this require also ion changes: Na influxes during the depolarization phase and K effluxes for the repolarization phase. Cl⁻ ions also diffuse into the sarcoplasm to aid the repolarization phase. During intense muscle contraction, the ion pumps that maintain homeostasis of these ions are inactivated and this (with other ion related disruption) causes ionic disturbances. This causes cellular membrane depolarization, inexcitability, and so muscle weakness.^[53] Ca²⁺ leakage from type 1 ryanodine receptor) channels has also been identified with fatigue.

Physical exercise may cause pain both as an immediate effect that may result from stimulation of free nerve endings by low pH, as well as a delayed onset muscle soreness. The delayed soreness is fundamentally the result of ruptures within the muscle, although apparently not involving the rupture of whole muscle fibers.
Muscle pain can range from a mild soreness to a debilitating injury depending on intensity of exercise, level of training, and other factors.
There is some preliminary evidence to suggest that moderate intensity continuous training has the ability to increase someones pain threshold.

Prevention
Delayed onset muscle soreness can be reduced or prevented by gradually increasing the intensity of a new exercise program, thereby taking advantage of the repeated-bout effect. Soreness can theoretically be avoided by limiting exercise to concentric and isometric contractions.But eccentric contractions in some muscles are normally unavoidable during exercise, especially when muscles are fatigued. Limiting the length of eccentric muscle extensions during exercise may afford some protection against soreness, but this may also not be practical depending on the mode of exercise. Static stretching or warming up the muscles before or after exercise does not prevent soreness.

Treatment
The soreness usually disappears within about 72 hours after appearing. If treatment is desired, any measure that increases blood flow to the muscle, such as low-intensity activity, massage, nerve mobilization,hot baths, or a sauna visit may help somewhat.
Immersion in cool or icy water, an occasionally recommended remedy, was found to be ineffective in alleviating DOMS in one 2011 study, but effective in another.There is also insufficient evidence to determine whether whole-body cryotherapy – compared with passive rest or no whole-body cryotherapy – reduces DOMS, or improves subjective recovery, after exercise.

Counterintuitively, continued exercise may temporarily suppress the soreness. Exercise increases pain thresholds and pain tolerance. This effect, called exercise-induced analgesia, is known to occur in endurance training (running, cycling, swimming), but little is known about whether it also occurs in resistance training. There are claims in the literature that exercising sore muscles appears to be the best way to reduce or eliminate the soreness, but this has not yet been systematically investigated.

Most importantly for recovery muscle fibers need good quality nutrition specially protein....
Exercise requires healthy muscles and protein in your diet is important for providing the building blocks (called amino acids) to repair, maintain and build muscle.
Our bodies don’t have a storage form for extra dietary protein so when we eat adequate amounts of carbohydrate and protein the carbohydrate provides the energy for your body to use the protein for its structural (bone, muscle) and functional (enzymes, hormones, transport molecules) properties. This means if you enjoy plenty of activity the protein you eat is available to repair, maintain and build muscle.
You can help with muscle recovery by consuming a snack containing both protein and carbohydrate after exercise. This will help with muscle repair and glycogen replacement, and can be as simple and inexpensive as a ham and salad sandwich. There is no need to buy expensive protein bars or shakes.
Including protein in a meal can affect hormones that suppress your appetite and prolong your sense of fullness helping with appetite control. Along with a good quality carbohydrate this can mean feeling fuller for longer with a steady energy supply to work, rest and play.
The Australian diet is adequate in high quality protein from both animal and plant sources. The trick is to choose lean cuts of meat, and add a vegetarian meal once a week for variety.

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