B. Saltin

Arterial Noradrenaline Concentration during Exercise in Relation to the Relative Work Levels

The noradrenaline (NA) levels in arterial blood plasma were followed at rest and during increasing muscular exercise in 5 healthy men. The levels were found to be significantly correlated to the oxygen consumption, measured at submaximal and calculated at supramaximal work. The NA levels increased slowly, up to about 75 % of the maximal oxygen consump tion, thereafter the NA levels increased rapidly. These increases are discussed with respect to increased sympathetic impulse flow, decreased inactivation of the circulating NA, and increased release from the nerve terminals per nerve impulse. At a work load requiring about 75 % or less of the maximal oxygen consumption the mean sympathetic impulse flow seems to be low. At the highest work loads (maximal to supramaximal) a markedly increased sympathetic impulse flow is of major importance for the rapidly increasing NA levels.

Physical Training in Sedentary Middle-aged and Older Men III. Cardiac Output and Gas Exchange at Submaximal and Maximal Exercise

Fifteen previously sedentary men (38–55 years old) participated in an endurance training program which consisted of running for 2–3 half-hours a week for 8–10 weeks. Maximal oxygen uptake increased in all subjects, mean increase from 2.68 to 3.06 l/min, i.e. 14 per cent. This increase was brought about by a 13 per cent increase in maximal cardiac output, from 18.7 to 21.1 l/min. Heart rate was 8–17 beats/min lower during submaximal exercise. The maximal heart rate decreased by 6 (from 182 to 176) beats/min. Thus stroke volume was increased 7–17 ml at submaximal and 17 ml (16 per cent) at maximal exercise. Heart volume determined from X-rays did not change. After the training, mean arterial blood pressure was on the average 5 mm Hg lower at a given submaximal oxygen uptake; no change was observed at maximal exercise.

Peak skeletal muscle perfusion is maintained in patients with chronic heart failure when only a small muscle mass is exercised

OBJECTIVESnThe issue to be resolved was whether peripheral leg blood flow in patients with chronic heart failure (CHF) is reduced by low local flow capacity or as a function of the amount of muscle mass activated during exercise.nnnMETHODS AND RESULTSnIn ten CHF patients (ejection fraction 26 (9)%), and 12 healthy controls central and peripheral circulatory responses were assessed during dynamic one- and two-legged knee extensor work. The patients reached a peak perfusion of 234 (16) ml 100 g-1 min-1 in the one-legged mode, which was similar to the controls (244 (11) ml 100 g-1 min-1). At peak two-legged work muscle perfusion was reduced in the patients by 24% (P < 0.05). In contrast the controls maintained their peak muscle perfusion. The mass of the quadriceps femoris muscle and peak leg blood flow correlated closely for both groups at peak one-legged work (r = 0.85, P < 0.001). Peak oxygen uptake in the active limb during one-legged exercise was similar for patients and controls (0.52 (0.06) vs. 0.63 (0.06) l min-1), but it was 38% lower (P < 0.05) in patients than controls during exhaustive two-legged exercise. Arterial systemic oxygen delivery (cardiac output x arterial oxygen content), at peak exercise was highly correlated with peak one- and two-legged workload for both groups, explaining 70% of the difference in peak workload attained (P < 0.001). At peak two-legged exercise non-exercising tissues of the body in the male CHF patients with the largest limb muscle mass, received a blood flow of only 1.2 (0.7) 1 min-1. Mean arterial blood pressure at peak work in both test conditions was significantly lower for the patients than the controls. A higher sympathetic nerve activity in the patients, as evaluated by arterial noradrenaline concentration (NA) and leg NA spillover, contributed to maintain the perfusion pressure.nnnCONCLUSIONSnPatients with moderate CHF can reach a peak skeletal muscle perfusion and a leg oxygen uptake comparable to that of healthy individuals when a sufficiently small muscle mass is activated. Exercise involving a larger muscle mass, for the patients in this study about 4 kg, markedly reduces peak leg blood flow, perfusion and oxygen uptake as well as blood flow to non-exercising organs and tissues.

Physical training in sedentary middle-aged and older men. I. Medical evaluation.

In a group of 68 middle-aged sedentary men participating for 2 months in hard physical training, 5 were initially advised against participation for medical reasons; 54 subjects completed the training program. The frequency of orthopaedic complications was high. A slight decrease of the number of abnormal ECG findings at rest and at work (premature beats and ST-changes) was found after training. The blood pressure reaction during work in relation to the heart rate response was not changed. A significant reduction of the iron and cholesterol levels in the serum occurred.

Aerobic and anaerobic exercise capacities of elite middle-distance runners after two weeks of training at moderate altitude

The effect of short‐term altitude training on sea‐level physiological characteristics in elite runners was investigated. Seven middle‐distance runners (6 men, 1 woman) belonging to the Swedish national team (mean age 23 years) spent 2 weeks of training at 2000 m above sea level in Kenya. Treadmill tests were performed before and 6 and 12 d after the altitude sojourn. Six other runners (4 men, 2 women) had a corresponding training sojourn at sea level in Portugal (control group). Ro of the runners (1 man, 1 woman) in the Kenya group were omitted from the study because of gastroenteritis. The maximal oxygen uptake (VO2 max; pretravel: Kenya group 212 and control group 188 ml · kg−0.75 ‐ min−1), maximal treadmill time and oxygen cost of running were unchanged in both groups. The maximal oxygen deficit increased in all subjects after the Kenya sojourn (mean 19±6%). Heart rates during running at specified submaximal running velocities were lower post‐altitude (Kenya group), but tended to be higher after sea‐level training (control group). Maximal heart rate was unchanged in both groups. Perceived exertion (Borg) during submaximal running was lower post‐altitude. Submaximal and maximal blood lactate and plasma catecholamine concentrations were not altered in any of the groups. Post‐exhaustive plasma ammonia levels were decreased 12 d after altitude descent in the Kenya group. The results suggest an unchanged aerobic capacity in elite middle‐distance runners after short‐term training at moderate altitude. However, a change in the circulatory regulation during submaximal exercise was observed. Furthermore, anaerobic capacity improved but this bore no clear relation to lactate or ammonia metabolism.

Free fatty acids and exercise.

Although the great explorers were well aware that eating fat was an efficient way to meet their large energy demand, it was not until some decades into this century that it could be demonstrated that lipids are metabolized directly by contracting skeletal muscles. The 1950s produced the first studies with [14C]-tagged fatty acids (FAs), proving that fat is transported into the cell as FAs. An FA-transporting protein that is present in the sarcolemma and in the cytoplasma has been identified. For FA transport into the mitochondria, carnitine and carnitine transferase are needed. It is still unclear how the use of lipids as an energy source for the muscle during exercise is limited. The supply of free fatty acids (FFAs) far exceeds what is taken up by the muscle. Seldom more than 2-4% of the amount of FFAs delivered to an exercising limb is taken up by the muscles and only part of it is oxidized. Physical training induces changes that enhance the uptake of FAs by the contracting muscles, and a larger fraction of this uptake is oxidized, but it is not yet clear which mechanism is behind this adaptation. What is known is that this uptake occurs despite no elevation in the amount of FA supplied to the limb.

The metabolic and circulatory response to beta-blockade in hypertensive men is correlated to muscle capillary density.

Both haemodynamic and metabolic variables have been shown to be related to the fibre composition and capillary density of skeletal muscle in man. In the present study, the change of several metabolic variables during beta-blockade was investigated and related to muscle fibre composition and capillary density in 28 men with essential hypertension. They had been given atenolol (50 mg/day) or metoprolol (200 mg/day) or propranolol (160 mg/day) for 4-12 months. Serum triglycerides increased during treatment and individual changes were significantly inversely correlated with capillary density. Insulin concentrations in the fasting state and at the end of an i.v. glucose tolerance test were significantly higher during beta-blockade, and individual changes were inversely correlated with capillary density. Furthermore, body weight increased and heart rate decreased, changes that were also correlated with capillary density. It is concluded that many of the previously but poorly understood large interindividual differences in response to beta-blocker treatment may be explained by the degree of development of the capillary net in muscle tissue. Obesity, physical training as well as genetic factors are known determinants of capillary density.

Carbohydrate and fat metabolism in contracting canine skeletal muscle

SummaryIsolated canine gracilis muscles were perfused in situ with a free flow (systemic blood flow; FF) or a constant flow (blood from a reservoir; CF). The nervous supply was stimulated electrically for 60 min. A-V-concentration differences for glucose, pyruvate, lactate, glycerol, FFA and O2 were obtained as well as the concentrations of ATP, CP, glycogen and lactate in the muscle.Resting O2 uptake ranged from 4 to 11 μmoles×100 g−1×min−1 (FF; CF). A 30- and 5-fold increase in O2 uptake occurred during stimulation in the FF and CF-experiments, respectively. The release of lactate was, however, the same (20–40 μmoles×100 g×min−1) although the muscle lactate concentration was much higher in the CF experiments. In the CF experiment stimulation did not significantly increase glucose uptake which ranged from 0.3 to 3.3 μmoles×100 g−1 ×min−1 at rest. Conversely, stimulation resulted in a 6-fold increase in glucose uptake in the FF experiments. No definite tendency for a FFA uptake or a glycerol release was found in either experiment (FF, CF). Glycogen depletion during the stimulation period amounted to 20–30 μmoles×g−1. Thus the glucose uptake could account for only 12% of the carbohydrate utilized during the stimulation period.

Sedentary lifestyle: an underestimated health risk.

During the last two centuries dramatic changes have occurred in the industrialized countries with regard to the role of exercise and physical activity in the daily life of man. Mechanization and electronic development have reduced manual labour at the work-site as well as at home, and walking or bicycling are no longer common modes of transportation. Instead, various forms of physical activity have developed and are practised in leisure time, either merely as recreation or competitively. Man is built for exercise! The largest single tissue of the body is muscle, and a large portion of the CNS is devoted to motor control. An interesting sphere of biological questions relates to how various tissues of the body adjust to altered demands. Within this realm of qucstions. one which has attracted much attention in clinical medicine is whether lack of physical activity is a risk factor for cardiovascular disease (CVD), and recently also for overall mortality. Soon after the Second World War, several epidemiological studies were published relating physical demands during working hours to cardiovascular health r1-31. For example, when comparing bus drivers with conductors in the London double deckers, and lowand high-physical-demand work among kibuttzers in Israel and long shore men in San Francisco, significantly less coronary heart disease (CHD) was found in those who were physically active in their jobs. The flaw with these studies and others using the degree of manual labour on the work-site is that selection has, or may have, affected the results, i.e. either that those remaining in the jobs are different from the general population and less prone to develop CHD, or that those with early symptoms of disease shift to less strenuous jobs. This problem was analysed in detail by Taylor et nl. in the US rail-road study. A meta-analysis summarizing the impact of physical activity in occupational cohort studies found the relative risk for death due to CHD to be 1.9 (95% C.1. = 1.6 2.8) for no activity versus high activity

ENERGY NEED, DELIVERY, AND UTILIZATION IN MUSCULAR EXERCISE

Publisher Summary A large number of independent factors may limit mans ability to perform physical work. At the onset of exercise, oxygen uptake increases gradually, and within a couple of minutes, it reaches a new level that is proportional to the performed work. Adipose tissue is the largest source of energy. The adrenergic neurohumoral system is considered to have a key position as a physiological regulator of the enhanced lipolysis in adipose tissue during exercise. One reason for this is that catecholamines are potent lipolytic agents in several species, including dog and man. The blood level of norepinephrine increases during physical activity, especially at workloads requiring large amounts of oxygen uptake. The level of circulating norepinephrine may predominantly reflect the activity in the sympathetic nerves as diffusion and overflow from the nerve terminals to the blood appear to be the principal inactivating mechanisms for the adrenergic transmitter, especially during exercise. Changes in the plasma concentration of epinephrine reflect the activity in the adrenal glands only. A change in the physical activity from rest to exercise elicits a rapid elevation of the glycerol concentration in plasma and an increased rate of free fatty acid turnover.