Scientifically measuring weight loss speed: physiological limits, overtraining identification, and the logic of rest intervals during aerobic exercise.

Provided that health is maintained, a 28-day exercise cycle can result in a weight loss of 8% to 10% of one's body weight. This is based on data observations over the past 10 years. Previously, some literature suggested that a weight loss of about 0.5 kg per week, or 2 kg per month, was a suitable rate of weight loss. However, data from nearly 10 years of closed-loop weight loss programs show that losing 8% to 10% of body weight in a 28-day cycle has no abnormal physical reactions, and related health indicators reach or approach normal ranges. Therefore, losing 8% to 10% of body weight in a 28-day exercise cycle is entirely possible and healthy.

Generally, a weight loss rate of 1.0% to 3.5% of one's body weight per week (7 days) is considered acceptable. This is because the rate of weight loss varies from person to person, depending not only on the design and execution of the exercise plan but also on individual differences. Even for the same person, the rate of weight loss can differ at different stages. Therefore, a weight loss rate of 1.0% to 3.5% of one's body weight per week (7 days) is acceptable. The rate of weight loss is relatively faster in the first two weeks and slower in the following weeks. However, as long as it remains within this range, it is acceptable. If the weight loss is less than 1.0% per week, the reasons should be analyzed. Besides personal factors and individual differences, the rationality of the exercise plan should also be considered. Regardless of the speed of weight loss, dieters should maintain a calm mindset, actively face weight changes, carefully analyze the reasons, and avoid being impatient or giving up halfway.

Physical exercise involves various forms of contraction and relaxation of skeletal muscles, regulated by the nervous system, to stretch bones and overcome resistance. Appropriate physical activity induces corresponding adaptive changes in skeletal muscles and related organs, such as stronger bones, increased bone density, skeletal muscle hypertrophy, and improved cardiovascular function. Overtraining or over-exercising refers to a state where the intensity or volume of exercise exceeds the body's tolerance, leading to adverse reactions in bodily functions. Under such conditions, the body experiences a series of adverse reactions, such as immune system imbalance, decreased cardiovascular function, reduced nervous system regulation, endocrine disorders, imbalances in metabolism and energy metabolism, and decreased athletic ability; in severe cases, it can negatively impact health.

Exercise leads to increased skeletal muscle cell thickness due to increased synthesis of intracellular protein components, particularly contractile proteins such as myosin. Muscle protein synthesis is a complex process regulated by a series of neuroendocrine system functions. Muscle protein synthesis requires raw materials-various amino acids-which enter the muscle cell under the influence of insulin and are assembled into proteins on ribosomes under the direction of endocrine hormones such as testosterone. During overtraining, endocrine function is disrupted, testosterone levels decrease, and the synthesis of contractile proteins significantly declines. This makes it impossible to achieve the muscle hypertrophy effect of exercise. Excessive strength training can even cause a significant loss of muscle protein, resulting in muscle volume decreasing rather than increasing.

While exercise does indeed burn fat through muscle movement, it has strict requirements regarding intensity, duration, and frequency. Over-exercising is generally avoided. Over-exercising significantly impacts exercise quality and can even affect the exerciser's mental state, making effective weight loss impossible. Furthermore, it increases the risk of sports injuries, hindering continued weight loss efforts. More exercise does not necessarily mean better results. In short, weight loss through exercise must be scientific and reasonable; unscientific exercise or unreasonable dieting will not yield satisfactory results.

Regarding over-exercising, we should pay more attention to its adverse reactions on the body. Exercise within your limits and choose a variety of sports to ensure sustainable exercise effects and achieve fitness and fat loss goals. Prolonged aerobic exercise does not mean that exercise must be completely uninterrupted. Short rest periods are essential, with rest periods of no more than 5 minutes, and every 30 to 45 minutes. The purpose of rest includes resting energy reserves. Short rest periods during continuous exercise can quickly restore phosphagen, and it only takes 2-3 minutes to fully recover to pre-exercise levels.

Promote lactic acid metabolism. Even during prolonged aerobic exercise, lactic acid is inevitably produced at the beginning, leading to muscle fatigue. Prolonged training without rest can damage muscles, and the body may be forced to stop due to inability to continue. Replenish fluids. During exercise, the body becomes dehydrated due to sweating and water evaporation. Replenish 100-200 ml of water during each rest period. If exercise exceeds one hour, replenish electrolytes to prevent muscle fatigue and decreased coordination caused by significant electrolyte loss.

If you've just started exercising to lose weight, or haven't exercised for a long time, you can appropriately increase the frequency of rest, taking a 2-minute break every 15 minutes. This rest should not be done sitting or lying down; it should be active rest. Simply put, it's about achieving a resting effect by reducing the intensity of your exercise. For example, if you're jogging at 6 km/h, you can choose to walk at 3 km/h as an active rest. Studies have confirmed that active rest eliminates accumulated lactic acid twice as quickly as resting at rest.

This rest differs from the cool-down period after exercise. Cool-down involves gentle movements or stretching exercises to gradually restore the body's muscles to a resting state. However, rest during exercise does not allow the body to return to a resting state. If you suddenly stop exercising at a certain intensity and stand still immediately, it will significantly affect venous blood return, reduce cardiac output, and cause physical discomfort such as dizziness and nausea, or even serious consequences such as orthostatic hypotension.