Home of Sports Medicine and Exercise Physiology

Erase Age with Exercise
A snapshot of all the ways staying fit can keep you healthy for years:

1- Better Memory:

Exercising at least 3 times a week at a moderate to high intensity can reduce odds of mental decline like dementia by 46%, according to a study of adults over the age of 55.

2- Stronger Bones:

Lifting weights twice a week can boost bone density and decrease falls by 40%, reports a study of 246 women ages 65 and older. Participants also stretched and did balance exercises 2 days a week.

3- Healthier Body:

Women who walk at a brisk pace at age 60 are up to 200% more likely to remain disease free at age 70, compared with casual walkers, found the Nurses Health Study.

by JC/ Prevention Magazine

During short-term, high-intensity exercise, lactate accumulates as the result of lactic acid production being greater than its removal. At a physiological pH, lactic acid, a strong organic acid, dissociates a proton (H+). It is the H+ rather than the lactate ion that causes pH to decrease. Although lactate accumulation in blood is directly related to H+ accmnulation in blood because the muscle cell membrane exports into blood both lactate anions and protons, in muscle the cause of acidosis is different. All the glycolytic intermediates of glycolysis are weak organic acids and dissociate protons. Further, as pointed out by Cevers (1977), the degradation of ATP results in H+ formation. Thus, lactate accumulation is associated with acidosis for more than one reason, but it is important to recognize that it is unbuffered protons (i.e., H+), not lactate anions, that pose difficulties for the performer.
The H+ accumulation resulting from glycolysis and ATP catabolism as the result of lactic acid production can have several negative effects. Within the muscle, the lower pH may inhibit phosphofructokinase (FFK) and slow glycolysis. In addition, H + may act to displace Ca 2+ from Troponin, thereby interfering with muscle contraction. Further, the low pH may stimulate pain receptors.
Hydrogen ion liberated into the blood and reacting in the brain causes severe side effects, including pain, nausea, and disorientation. Within the blood itself, H+ inhibits the combination of O2 with hemoglobin in the lungs. Some species actually run themselves to the point where O2 delivery is reduced by lactic acid formation and the blocking of oxyhemoglobin fonnation. High circulating H+ levels also thwart the action of hormone-sensitive lipase activity in adipose tissue by stimulating phosphodiesterase and the reesterification of fatty acids to triglycerides. The net result is a limiting of the release of free fatty acids (FFA) into the circulation. Fat oxidation in muscle is directly dependent on circulating FFA levels.
As debilitating as high levels of H + from lactic acid dissociation may be in the muscles and blood, it is uncertain whether the pH decrement actually stops exercise. Because of a muscle’s gross and microanatomy, muscle biopsies actually yield little information on the pH at critical sites of metabolism. Many active sites on enzymes are hydrophobic, and the environment pH has minimal effect. In theory, a lowered cytoplasmic pH should benefit mitochondrial function. Recent studies utilizing nuclear magnetic resonance (NMR) technique to look within muscles noninvasively during exercise and recovery suggest that fatigue is due to CF depletion, as noted, rather than to lactic acid accumulation.
Muscle and blood lactate accumulation during exercise are symptomatic of more than muscle and blood acidosis. Lactate accumulation means that the mechanisms of lactate disposal and clearance have been exceeded. Thus, the overall system is failing to cope with metabolic demands. Further, lactate accumulation is indicative of glycogen depletion, as noted.

Source: McGraw Hill, Brooks, Fahey, Baldwin – Exercise Physiology, Human Bioenergetics and Its applications – Fourth Ed(book)

Figure 1 - Metabolism and Heat Production in a body at rest.

Physical exercise represents a special metabolic situation. As Figure 1 indicates, for a body at rest, all the energy liberated within appears as heat. If metabolism is constant, the quantity of heat produced within the body over a period of time will be the same as that leaving the body. However, during exercise, some of the energy liberated within the body appears as physical work outside the body. Therefore, devices to measure external work performed, such as bicycle ergometers (Figure 2, Figure 3) and treadmills (Figure 4, Figure 5), are used.

Figure 2 – bicycle ergometer  indirect calorimetry

Figure 3 – bicycle ergometer indirect calorimetry

During exercise, direct calorimeters such as the Atwater—Rosa calorimeter (Figure 6) are of little use for several reasons. First, such devices are very expensive. Second, the heat generated by an ergometer, if it is electrically powered, may far exceed that of the subject. Third, body temperature increases during exercise because not all the heat produced is liberated from the body. Therefore, the sensors in the walls of the calorimeter do not pick up all the heat produced. Finally, the body sweats during exercise, which also affects the calorimeter and changes body mass. Changes in body mass and the unequal distribution of heat within the body make it very difficult to use direct calorimetry in exercise.

Figure 6 - Atwater—Rosa calorimeter