The effects of physical exercise on the immune system

Physical exercise has numerous effects on the human body, including the immune system. After strenuous exercise, athletes pass through a period of impaired immune resistance. During this period, athletes are theoretically more susceptible to upper respiratory tract infections, although a causal relation has never been demonstrated. Moderate exercise seems to have a beneficial effect on the immune function, which could protect against upper respiratory tract infections. Exercise has effects on both the humoral and the cellular immune system. Doping products, except glucocorticoids, only have modest effects on the immune system, although erythropoietin may, in rare cases, cause severe side-effects. Glutamine and vitamin C could, hypothetically, prevent the negative effects of strenuous exercise on the immune function, but further studies are needed to demonstrate and explain these effects.     

Indicators of cell breakdown in plasma of men during and after a marathon race

Plasma indicators of muscle cell leakage and of hemolysis were studied in 23 runners before and after a marathon race. Blood samples were drawn from an antecubital vein the morning before the race (baseline), at 3 p.m., i.e., 2 h before the start, on arrival, 12 and 36 h, and 7 days later. Compared with the baseline values, the plasma creatinine phosphokinase MM and MB subfractions, aldolase and glutamicoxaloacetic transaminase activity were increased immediately after the race, rose further 12 h after the marathon, and remained elevated the race, rose further 12 h after the marathon, and remained elevated 36 h and 7 days later. The plasma lactate dehydrogenase activity and myoglobin concentration were increased on arrival and returned to the pre-race activity 7 days after the marathon. Compared with the pre-race values, the plasma haptoglobin concentration was decreased immediately and 12 h after the marathon. Our data show that indicators of muscle cell leakage and of hemolysis in plasma, withdrawn after a marathon race, remained elevated for up to 7 days after the race.     

Effect of creatine supplementation on creatine and glycogen content in rat skeletal muscle

The effects of high dose creatine feeding (5 g kg(-1) BW day(-1), 5 days) on creatine content, glucose transport, and glycogen accumulation in white gastrocnemius, red gastrocnemius and soleus muscles of the rat was investigated. Isolated rat hindquarters of creatine fed and control rats were perfused with a standard medium containing either insulin alone (0, 100 or 20 000 microU mL(-1)) or in combination with creatine (2 or 10 mmol L(-1)). Furthermore, plasma insulin concentration was measured in normal rats during creatine feeding, as well as in anaesthetized rats during intravenous creatine infusion. Five days of creatine feeding increased (P < 0.05) total creatine content in soleus (+ 20%) but not in red gastrocnemius (+15%, n.s.) and white gastrocnemius (+ 10%, n.s.). In parallel, glycogen content was markedly elevated (P < 0.05) in soleus (+ 40%), less (P < 0.05) in red gastrocnemius (+ 15%), and not in white gastrocnemius (+ 10%, n.s.). Glucose transport rate, muscle GLUT-4 content, glycogen synthase activity in perfused muscles and glycogen synthesis rate were not significantly altered by creatine feeding in either muscle type. Furthermore, high dose creatine feeding raised (P < 0.05) plasma creatine concentration fivefold but did not alter circulating insulin level. It is concluded that short-term high dose creatine feeding enhances creatine disposal and glycogen storage in rat skeletal muscle. However, the creatine and glycogen response to creatine supplementation is markedly greater in oxidative than in glycolytic muscles.     

Short- and long-term evolution of body composition in 1389 obese outpatients following a very low calorie diet (Pro'gram18 VLCD)

One thousand three-hundred and eighty-nine obese outpatients were followed by 28 practitioners. They were enrolled in a multidisciplinary weight control program for at least 1 year. The major components of the program include a commercial very low calorie diet (Pro'gram18 VLCD), behavior modification, and exercise. There was a significant decrease in body weight compared with baseline of approximately 12.3+/-5.3 kg at the end of the maintenance period; the weight loss was achieved essentially at the expense of fatty mass, -10.3+/-5.5 kg at 90 days while fat-free mass loss was -2.0+/-2.5 kg at 90 days. Mean serum total cholesterol and triglycerides were also lowered and systolic and diastolic blood pressure and fasting blood glucose values were normalized at the end of the weight-loss phase. Obese outpatients lost substantial amounts of weight using VLCD, reduced the risk factors associated with obesity, and had encouraging long-term results, with weight loss maintained at 2-year follow-up.     

Sodium bicarbonate improves sprint performance in endurance cycling

ObjectivesOral sodium bicarbonate intake (NaHCO₃) may improve performance in short maximal exercise by inducing metabolic alkalosis. However, it remains unknown whether NaHCO₃ also enhances all-out performance at the end of an endurance competition. Therefore, the present study investigated the effect of stacked NaHCO₃ loading on sprint performance following a 3-h simulated cycling race.DesignDouble-blind randomized placebo-controlled cross-over study.MethodsEleven trained male cyclists (22.3 (18.3–25.3) year; 73.0 (61.5–88) kg; VO₂max: 63.7 (57–72) ml kg^?1 min^?1) ingested either 300 mg kg^?1 body weight NaHCO₃ (BIC) or NaCl (PL). NaHCO₃ or NaCl was supplemented prior to (150 mg kg^?1) and during (150 mg kg^?1) a 3-h simulated cycling race with a 90-s all-out sprint (90S) at the end. Capillary blood samples were collected for determination of blood pH, lactate and HCO₃^? concentrations. Analysis of variance (lactate, pH, HCO₃^?) and paired t-test (power) were applied to compare variables across condition (and time).ResultsNaHCO₃ intake improved mean power during 90S by ～3% (541 ± 59 W vs. 524 ± 57 W in PL, p = 0.047, Cohen’s D = 0.28, medium). Peak blood lactate concentration and heart rate at the end of 90S were higher (p < 0.05) in BIC (16.2 ± 4.1 mmol l ¹, 184 ± 7 bpm) than in PL (12.4 ± 4.2 mmol l^?1, 181 ± 5 bpm). NaHCO₃ ingestion increased blood [HCO₃^?] (31.5 ± 1.3 vs. 24.4 ± 1.5 mmol l^?1 in PL, p < 0.001) and blood pH (7.50 ± 0.01 vs. 7.41 ± 0.03 in PL, p < 0.05) prior to 90S.ConclusionsNaHCO₃ supplementation prior and during endurance exercise improves short all-out exercise performance at the end of the event. Therefore, sodium bicarbonate intake can be applied as a strategy to increase success rate in endurance competitions.     

Effect of prolonged physical exercise on intra-erythrocyte and plasma potassium

Summary The intracellular concentrations of sodium [Na⁺] and potassium [K⁺] and the water content in human erythrocytes were investigated in 21 male runners before and after a marathon. From 2 to 5 min after the race, the intra-erythrocyte [K⁺] was significantly decreased (p<0.001) by 7% whereas the plasma [K⁺], intra-erythrocyte [Na⁺] and the erythrocyte water content were unchanged. The change in the intra-erythrocyte [K⁺] observed immediately after the marathon, was negatively correlated with the race time (r=−0.44;p<0.05). Furthermore, the change in the plasma [K⁺] (r=−0.64;p<0.001) and the amount of K⁺ excreted in the urine during the race (r=0.54;p<0.05) were also, respectively, negatively and positively correlated with the race time. It is concluded that during prolonged physical exercise the erythrocytes could serve as a kind of K⁺ reservoir that is drained with increasing magnitude of body K⁺ loss. This might explain why in the faster marathon runners, in whom the urinary K⁺ loss is smaller and the K⁺ intake is greater than in the slower runners during race, the intra-erythrocyte [K⁺] is unchanged after a marathon whereas in the slower runners it is decreased.     

Phosphocreatine resynthesis is not affected by creatine loading

PURPOSE: Oral creatine supplementation has been shown to improve power output during high intensity intermittent muscle contractions. Facilitated muscle phosphocreatine (PCr) resynthesis, by virtue of elevated intracellular PCr concentration, might contribute to this ergogenic action. Therefore, the effect of creatine loading (C: 25 g X d(-1) for 5 d) on muscle PCr breakdown and resynthesis and muscle performance during high intensity intermittent muscle contractions was investigated. METHODS: A double-blind randomized cross-over study was performed in young healthy male volunteers (N = 9). 31P-NMR spectroscopy of the m. gastrocnemius and isokinetic dynamometry of knee-extension torque were performed before and after 2 and 5 d of either placebo (P) or C administration. RESULTS: Compared with P, 2 and 5 d of C increased (P < 0.05) resting muscle PCr concentration by 11% and 16%, respectively. Furthermore, torque production during maximal intermittent knee extensions, including the first bout of contractions, was increased (P < 0.05) by 5-13% by either 2 or 5 d of C. However, compared with P, the rate of PCr breakdown and resynthesis during intermittent isometric contractions of the calf was not significantly affected by C. CONCLUSION: Creatine loading raises muscle PCr concentration and improves performance during rapid and dynamic intermittent muscle contractions. Creatine loading does not facilitate muscle PCr resynthesis during intermittent isometric muscle contractions.