Neuromuscular fatigue and recovery after strenuous exercise depends on skeletal muscle size and stem cell characteristics

Hamstring muscle injury is highly prevalent in sports involving repeated maximal sprinting. Although neuromuscular fatigue is thought to be a risk factor, the mechanisms underlying the fatigue response to repeated maximal sprints are unclear. Here, we show that repeated maximal sprints induce neuromuscular fatigue accompanied with a prolonged strength loss in hamstring muscles. The immediate hamstring strength loss was linked to both central and peripheral fatigue, while prolonged strength loss was associated with indicators of muscle damage. The kinematic changes immediately after sprinting likely protected fatigued hamstrings from excess elongation stress, while larger hamstring muscle physiological cross-sectional area and lower myoblast:fibroblast ratio appeared to protect against fatigue/damage and improve muscle recovery within the first 48 h after sprinting. We have therefore identified novel mechanisms that likely regulate the fatigue/damage response and initial recovery following repeated maximal sprinting in humans.

Sprint interval and traditional endurance training increase net intramuscular triglyceride breakdown and expression of perilipin 2 and 5

Intramuscular triglyceride (IMTG) utilization is enhanced by endurance training (ET) and is linked to improved insulin sensitivity. This study first investigated the hypothesis that ET-induced increases in net IMTG breakdown and insulin sensitivity are related to increased expression of perilipin 2 (PLIN2) and perilipin 5 (PLIN5). Second, we hypothesized that sprint interval training (SIT) also promotes increases in IMTG utilization and insulin sensitivity. Sixteen sedentary males performed 6 weeks of either SIT (4-6, 30 s Wingate tests per session, 3 days week(-1)) or ET (40-60 min moderate-intensity cycling, 5 days week(-1)). Training increased resting IMTG content (SIT 1.7-fold, ET 2.4-fold; P < 0.05), concomitant with parallel increases in PLIN2 (SIT 2.3-fold, ET 2.8-fold; P < 0.01) and PLIN5 expression (SIT 2.2-fold, ET 3.1-fold; P < 0.01). Pre-training, 60 min cycling at ∼65% pre-training decreased IMTG content in type I fibres (SIT 17 ± 10%, ET 15 ± 12%; P < 0.05). Following training, a significantly greater breakdown of IMTG in type I fibres occurred during exercise (SIT 27 ± 13%, ET 43 ± 6%; P < 0.05), with preferential breakdown of PLIN2- and particularly PLIN5-associated lipid droplets. Training increased the Matsuda insulin sensitivity index (SIT 56 ± 15%, ET 29 ± 12%; main effect P < 0.05). No training × group interactions were observed for any variables. In conclusion, SIT and ET both increase net IMTG breakdown during exercise and increase in PLIN2 and PLIN5 protein expression. The data are consistent with the hypothesis that increases in PLIN2 and PLIN5 are related to the mechanisms that promote increased IMTG utilization during exercise and improve insulin sensitivity following 6 weeks of SIT and ET.

The role of 'African chemists' in the health care system of the Eastern Cape province of South Africa

Self-medication is documented as an integral part of health care therapy in developing countries such as Ethiopia, Cameroon, Uganda and Mexico. In South Africa the types of illnesses and health problems that are referred to both traditional healers and biomedical practices have been well documented. However, very little literature exists on self-diagnosis, self-medication or sources of the medicines used for self-medication. This bias in the literature has come about largely because anthropological studies have focused on the later stages of the illness referral system when treatment is sought from a specialist for symptoms which have not responded to forms of self-medication. As a result of this, health care studies have documented the more exceptional exotic healing rituals and culturally bound syndromes of a particular society or community, and not discussed the more ordinary practices of self-medication of everyday illness. Self-medication is however an important initial response to illness and many illnesses are successfully managed at this stage. Amayeza stores (singular-iyeza store)--or 'African chemists'--are an important source of medicines for self-diagnosed illnesses. The current discussion focuses on the types of medicines and treatments that are obtained from amayeza stores without professional consultation in the Eastern Cape province of South Africa.

Vasoconstrictor role for vasopressin in experimental heart failure in the rabbit

Vasopressin's role as a vasoconstrictor in chronic heart failure, was examined in rabbits with adriamycin cardiomyopathic congestive heart failure. Chronic adriamycin treatment resulted in a decrease in cardiac output (829 +/- 38-610 +/- 36 ml/min, P less than 0.005) and blood pressure (83 +/- 2-76 +/- 3 mmHg, P less than 0.01), and an increase in peripheral resistance (8,377 +/- 381-10,170 +/- 657 dyn-s-cm-5, P less than 0.05). Plasma renin activity (4.7 +/- 0.6-10.9 +/- 2.8 ng angiotensin I/ml X h) and norepinephrine (0.7 +/- 0.1-1.3 +/- 0.2 pmol/ml, P less than 0.05) increased while plasma vasopressin levels did not change. Vasopressin infusion, however, produced significantly greater increases in peripheral resistance in animals with heart failure than in controls. Moreover, a specific vasopressin vascular antagonist reduced blood pressure (7 +/- 3%) and peripheral resistance (14 +/- 4%) and increased cardiac output (10 +/- 3%) in animals with heart failure but had no cardiovascular effects in normal rabbits. These results suggest that vascular sensitivity to vasopressin is increased in heart failure, and that it contributes significantly to the increased afterload in heart failure despite normal plasma levels. In this model of severe, chronic heart failure the sympathetic, renin-angiotensin, and vasopressin systems all appear to be activated.

Adriamycin cardiomyopathy in the rabbit: an animal model of low output cardiac failure with activation of vasoconstrictor mechanisms

Chronic administration of intravenous adriamycin (1 mg . kg-1 twice weekly for 8 weeks) to rabbits resulted in a cardiomyopathy which was similar to that occurring in patients with adriamycin cardiotoxicity. We studied systemic and renal haemodynamics and the activation of vasoconstrictor mechanisms reflected by changes in plasma renin activity (PRA), noradrenaline (NA) and vasopressin (AVP) levels during the development of heart failure in this animal model. By 8 weeks cardiac failure was clearly established. At postmortem all animals had dilated hearts, pleural and pericardial effusions, ascites and hepatic congestion. Heart weights were increased (8.1 +/- 0.7 g in treated animals n = 9 vs 6.0 +/- 0.2 g in controls n = 9 p less than 0.05). Cardiac output (measured by thermodilution) fell at 8 weeks from 799 +/- 61 ml . min-1 to 624 +/- 44 ml . min-1 (n = 6 p less than 0.05) with a parallel fall in mean blood pressure from 85 +/- 2 mmHg to 75 +/- 4 mmHg. Total peripheral resistance rose in four of the six rabbits. Renal blood flow fell from 108 +/- 4 ml . min-1 to 61 +/- 6 ml . min-1 (p less than 0.05) by 8 weeks. Renal vascular resistance increased in all animals. PRA increased from 5.1 +/- 0.5 ng AI . ml-1 . h-1 to 11.6 +/- 2.6 ng AI . ml-1 . h-1 by 4 weeks (p less than 0.05) and remained elevated thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)