Anders Sjödin

Effects of physical exercise on phospholipid fatty acid composition in skeletal muscle

The effects of low-intensity exercise on the fatty acid composition in skeletal muscle and in serum were studied in 19 sedentary, middle-aged Swedish men. During a 10-wk period, all subjects were given a standardized diet with an identical fat composition. After 4 wk on this diet, they were randomly allocated to a daily exercise program (55% peak oxygen uptake) or to continue to live a sedentary life for the remaining 6 wk. Aerobic capacity (submaximal bicycle test) and peripheral insulin sensitivity (hyperinsulinemic euglycemic clamp) improved with training, whereas the body weight as well as the body composition (underwater weighing and bioimpedance) were unchanged. The proportions of palmitic acid (16:0) and linoleic acid [18:2(n-6)] and the sum of n-6 fatty acids [18:2(n-6), 20:3(n-6), 20:4(n-6)] were decreased in skeletal muscle phospholipids, whereas the proportion of oleic acid [18:1(n-9)] was increased, by training. The fatty acid profile in skeletal muscle triglycerides remained unchanged. We conclude that regular low-intensity exercise influences the fatty acid composition of the phospholipids in skeletal muscle, which hypothetically may contribute to changes of the skeletal muscle membrane fluidity and influence the peripheral insulin sensitivity.The effects of low-intensity exercise on the fatty acid composition in skeletal muscle and in serum were studied in 19 sedentary, middle-aged Swedish men. During a 10-wk period, all subjects were given a standardized diet with an identical fat composition. After 4 wk on this diet, they were randomly allocated to a daily exercise program (55% peak oxygen uptake) or to continue to live a sedentary life for the remaining 6 wk. Aerobic capacity (submaximal bicycle test) and peripheral insulin sensitivity (hyperinsulinemic euglycemic clamp) improved with training, whereas the body weight as well as the body composition (underwater weighing and bioimpedance) were unchanged. The proportions of palmitic acid (16:0) and linoleic acid [18:2(n-6)] and the sum of n-6 fatty acids [18:2(n-6), 20:3(n-6), 20:4(n-6)] were decreased in skeletal muscle phospholipids, whereas the proportion of oleic acid [18:1(n-9)] was increased, by training. The fatty acid profile in skeletal muscle triglycerides remained unchanged. We conclude that regular low-intensity exercise influences the fatty acid composition of the phospholipids in skeletal muscle, which hypothetically may contribute to changes of the skeletal muscle membrane fluidity and influence the peripheral insulin sensitivity.

The effect of different blood sampling sites and analyses on the relationship~ between exercise intensity and 4.0 mmol ·1− blood lactate concentration

SummaryThe aim of the study was to examine whether the difference in lactate concentration in different blood fractions is of practical importance when using blood lactate as a test variable of aerobic endurance capacity. Ten male firefighters performed submaximally graded exercise on a cycle ergometer for 20–25 min. Venous and capillary blood samples were taken every 5 min for determination of haematocrit and lactate concentrations in plasma, venous and capillary blood. At the same time, expired air was collected in Douglas bags for determination of the oxygen consumption. A lactate concentration of 4.0 mmol·1−1 was used as the reference value toi compare the oxygen consumption and exercise intensity when different types of blood specimen and sampling sites were used for lactate analysis. At this concentration the exercise intensity was 17% lower (P<0.01) when plasma lactate was compared toi venous blood lactate, and 12% lower (P<0.05) when capillary blood lactate was used. Similar discrepancies were seen in oxygen consumption. The results illustrated the importance of standardizing sampling and handling of blood specimens for lactate determination to enable direct comparisons to be made among results obtained in different studies.

Coenzyme Q10 supplementation and exercise-induced oxidative stress in humans

OBJECTIVE The theoretically beneficial effects of coenzyme Q10 (Q10) on exercise-related oxidative stress and physical capacity have not been confirmed to our knowledge by interventional supplementation studies. Our aim was to investigate further whether Q10 supplementation at a dose recommended by manufacturers influences these factors. METHODS Using a randomized, double-blind, controlled design, we investigated the effect on physical capacity of 8 wk of treatment with a daily dose of 90 mg of Q10 (n = 12) compared with placebo (n = 11) in moderately trained healthy men 19 to 44 y old. Two days of individualized performance tests to physical exhaustion were performed before and after the intervention. Primary outcomes were maximal oxygen uptake, workload, and heart rate at the lactate threshold. Secondary outcomes were creatine kinase, hypoxanthine, and uric acid. RESULTS No significant differences between the groups were discerned after the intervention for maximal oxygen uptake (-0.11 L/min, 95% confidence interval -0.31 to 0.08, P = 0.44), workload at lactate threshold (6.3 W, -13.4 to 25.9, P = 0.36), or heart rate at lactate threshold (2.0 beats/min, -4.9 to 8.9, P = 0.41). No differences between the groups were detected for hypoxanthine or uric acid (serum markers of oxidative stress) or creatine kinase (a marker of skeletal muscle damage). CONCLUSION Although in theory Q10 could be beneficial for exercise capacity and in decreasing oxidative stress, the present study could not demonstrate that such effects exist after supplementation with a recommended dose.

A suit calorimeter for energy balance studies on humans during heavy exercise

A modification of the suit calorimeter originally developed in 1972 was used in combination with indirect respiratory calorimetry. The modification included increased cooling capacity of the suit by means of an increased density of cooling tubes and a variable water flow pump which permitted higher flow rates. This has made the suit calorimeter a very effective heat exchanger that could be used for studies on high energy turnover during heavy exercise. Furthermore, specially designed absorption clothing made it possible to collect any sweat produced before it evaporated, thus minimizing potential error in measuring evaporative heat loss. The suit calorimeter would seem to offer a valuable tool in the analysis of the specific thermogenic responses to dietary changes and physical activity in studies on energy and protein metabolism and their interaction in humans. It also makes it possible to perform direct calorimetric measurements in metabolic balance studies using continuous parenteral infusion since the subjects do not need to be sealed in a calorimeter chamber.

Mild overcooling increases energy expenditure during endurance exercise

Intensive cooling has been shown to increase energy expenditure (EE) during work as well as to decrease physical performance. Two different levels of moderate cooling (10°C vs 15°C) were studied during light endurance exercise in order to examine the effect of the increased heat loss on EE. Twelve subjects performed a 90‐min low intensity exercise (100 W) on a cycle ergometer, wearing a water‐cooled calorimeter suit for controlled cooling. The lower temperature resulted in a 4.3±3.8% (mean±SD) higher EE, increased total heat loss and lowered skin temperatures. No differences in central core body temperature, heart rate or respiratory quotient (RQ) were recorded. There was a relation between differences in the rate of heat loss and the corresponding increase in EE. Even a small increase in cooling during endurance exercise increased EE which may be a relevant problem in winter sports.

Training Induced Changes in the Fatty Acid Composition of Skeletal Muscle Lipids

Insulin sensitivity relates to the fatty acid composition of the skeletal muscle phospholipids and the intramuscular triglyceride content. The fatty acid composition of the phospholipids--but not of the triglycerides--in the muscles are influenced by regular physical activity of low-moderate intensity. An increased degree of unsaturation of the cell membranes after training may hypothetically contribute to the improvement of insulin sensitivity. Different ways of reducing the supply of lipids in the muscles may possibly cause similar changes of the fatty acid composition of the cell membranes. Further studies are needed to explore the relationships between changes of the skeletal muscle lipid composition during physical activity, the interaction with dietary fat intake, and changes of insulin sensitivity and development of related metabolic disorders.