Elmarie Terblanche

Field and laboratory correlates of performance in competitive cross-country mountain bikers

Abstract We designed a laboratory test with variable fixed intensities to simulate cross-country mountain biking and compared this to more commonly used laboratory tests and mountain bike performance. Eight competitive male mountain bikers participated in a cross-country race and subsequently did six performance tests: an individual outdoor time trial on the same course as the race and five laboratory tests. The laboratory tests were as follows: an incremental cycle test to fatigue to determine peak power output; a 26-min variable fixed-intensity protocol using an electronically braked ergometer followed immediately by a 1-km time trial using the cyclists own bike on an electronically braked roller ergometer; two 52-min variable fixed-intensity protocols each followed by a 1-km time trial; and a 1-km time trial done on its own. Outdoor competition time and outdoor time trial time correlated significantly (r = 0.79, P < 0.05). Both outdoor tests correlated better with peak power output relative to body mass (both r = −0.83, P < 0.05) than absolute peak power output (outdoor competition: r = −0.65; outdoor time trial: r = −0.66; non-significant). Outdoor performance times did not correlate with the laboratory tests. We conclude that cross-country mountain biking is similar to uphill or hilly road cycling. Further research is required to design sport-specific tests to determine the remaining unexplained variance in performance.

A reappraisal of the blood glucose homeostat which comprehensively explains the type 2 diabetes mellitus–syndrome X complex

Blood glucose concentrations are unaffected by exercise despite very high rates of glucose flux. The plasma ionised calcium levels are even more tightly controlled after meals and during lactation. This implies ‘integral control’. However, pairs of integral counterregulatory controllers (e.g. insulin and glucagon, or calcitonin and parathyroid hormone) cannot operate on the same controlled variable, unless there is some form of mutual inhibition. Flip‐flop functional coupling between pancreatic α‐ and β‐cells via gap junctions may provide such a mechanism. Secretion of a common inhibitory chromogranin by the parathyroids and the thyroidal C‐cells provides another. Here we describe how the insulin:glucagon flip‐flop controller can be complemented by growth hormone, despite both being integral controllers. Homeostatic conflict is prevented by somatostatin‐28 secretion from both the hypothalamus and the pancreatic islets. Our synthesis of the information pertaining to the glucose homeostat that has accumulated in the literature predicts that disruption of the flip‐flop mechanism by the accumulation of amyloid in the pancreatic islets in type 2 diabetes mellitus will lead to hyperglucagonaemia, hyperinsulinaemia, insulin resistance, glucose intolerance and impaired insulin responsiveness to elevated blood glucose levels. It explains syndrome X (or metabolic syndrome) as incipient type 2 diabetes in which the glucose control system, while impaired, can still maintain blood glucose at the desired level. It also explains why it is characterised by high plasma insulin levels and low plasma growth hormone levels, despite normoglycaemia, and how this leads to central obesity, dyslipidaemia and cardiovascular disease in both syndrome X and type 2 diabetes.

The influence of sprint interval training on body composition, physical and metabolic fitness in adolescents and young adults with intellectual disability: a randomized controlled trial:

Objective: In this study we evaluated the effect of sprint interval training on metabolic and physical fitness in adolescents and young adults with intellectual disabilities when compared with continuous aerobic training and no training (control). Methods: Fifty-four persons with intellectual disabilities (age: 17 (3.0), body mass index: 27.7 (3.7), intelligence quotient: 59 (8.6)) were matched based on age, gender and intelligence quotient between sprint interval training (n = 17), continuous aerobic training (n = 15) and control (n = 14). Sprint interval training was composed of three blocks of 10 minutes at ventilatory threshold (blocks 1 and 3: 10 sprint bouts of 15 seconds, followed by 45 seconds relative rest; block 2: continuous training) twice a week for 15 weeks. Continuous aerobic training was composed of three blocks of 10 minutes continuous training. After eight weeks, intensity was increased to 110% of ventilatory threshold. The control group did not participate in supervised exercise training. Before and after the training period, body composition, physical and metabolic fitness were evaluated. Results: Sprint interval training showed a significant positive evolution for waist circumference, fat%, systolic blood pressure, lipid profile, fasting insulin, homeostasis model assessment of insulin resistance, peak VO2, peak Watt, ventilatory threshold, 6-minute walk distance and muscle fatigue resistance when compared with no training (P < 0.01). The sprint interval training group demonstrated significant improvements for fat%, systolic blood pressure, low-density lipoprotein, fasting insulin, peak VO2 and peak power and ventilatory threshold (P < 0.01) when compared with continuous aerobic training. Conclusion: In this study we could observe that sprint interval training has stronger beneficial effects on body composition, physical fitness and metabolic fitness compared with control. Compared with continuous aerobic training, sprint interval training seems to result in better outcome.

Estimation of maximal oxygen uptake by bioelectrical impedance analysis

Previous non-exercise models for the prediction of maximal oxygen uptake (

Paralympic Sprint Performance Between 1992 and 2012

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Selected Applications of Bioelectrical Impedance Analysis: Body Fluids, Blood Volume, Body Cell Mass and Fat Mass

) have failed to accurately discriminate cardiorespiratory fitness within large cohorts. The aim of the present study was to evaluate the feasibility of a completely indirect method for predicting

Analysis of South African semi-elite rugby head coaches’ engagement with performance analysis

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