Choice of sprint start performance measure affects the performance-based ranking within a group of sprinters: which is the most appropriate measure?

Sprint start performance has previously been quantified using several different measures. This study aimed to identify whether different measures could influence the performance-based ranking within a group of 12 sprinters, and if so, to identify the most appropriate measure. None of the 10 performance measures ranked all sprinters in the same order; Spearman's rho correlations between different block phase measures ranged from 0.50 to 0.94, and between block phase measures and those obtained beyond block exit from 0.66 to 0.85. Based on the consideration of what each measure quantifies, normalised average horizontal external power was identified as the most appropriate, incorporating both block velocity and the time spent producing this velocity. The accuracy with which these data could be obtained in an externally valid field setting was assessed against force platform criterion data. For an athlete producing 678 ± 40 W of block power, a carefully set-up manual high-speed video analysis protocol produced systematic and random errors of +5 W and ± 24 W, respectively. Since the choice of performance measure could affect the conclusions drawn from a technique analysis, for example the success of an intervention, it is proposed that external power is used to quantify start performance

Mechanical and neurophysiological effects of postural stretching

SCOPUS: cp.jinfo:eu-repo/semantics/publishe

Limiting mechanisms of force production after repetitive dynamic contractions in human triceps surae

The influence of repetitive dynamic fatiguing contractions on the neuromuscular characteristics of the human triceps surae was investigated in 10 subjects. The load was 50% of the torque produced during a maximal voluntary contraction, and the exercise ended when the ankle range of motion declined to 50% of control. The maximal torque of the triceps surae and the electromyographic (EMG) activities of the soleus and medial gastrocnemius were studied in response to voluntary and electrically induced contractions before and after the fatiguing task and after 5 min of recovery. Reflex activities were also tested by recording the Hoffmann reflex (H reflex) and tendon reflex (T reflex) in the soleus muscle. The results indicated that whereas the maximal voluntary contraction torque, tested in isometric conditions, was reduced to a greater extent (P < 0.05) at 20 degrees of plantar flexion (-33%) compared with the neutral position (-23%) of the ankle joint, the EMG activity of both muscles was not significantly reduced after fatigue. Muscle activation, tested by the interpolated-twitch method or the ratio of the voluntary EMG to the amplitude of the muscle action potential (M-wave), as well as the neuromuscular transmission and sarcolemmal excitation, tested by the M-wave amplitude, did not change significantly after the fatiguing exercise. Although the H and T reflexes declined slightly (10-13%; P < 0.05) after fatigue, these adjustments did not appear to have a direct deleterious effect on muscle activation. In contrast, alterations in the mechanical twitch time course and postactivation potentiation indicated that intracellular Ca(2+)-controlled excitation-contraction coupling processes most likely played a major role in the force decrease after dynamic fatiguing contractions performed for short duration.Journal ArticleResearch Support, Non-U.S. Gov'tIF 2004 :2.82info:eu-repo/semantics/publishe

Encéphalopathie de Gayet-Wernicke et anorexie mentale, présentation clinique particulière chez un adolescent.

Gayet-Wernicke's encephalopathy is a neurological condition caused by a deficit in vitamin B1, occurring most frequently in alcoholic patients. Although rare, its description is also known in the pediatric population where it is often associated with cancers, gastrointestinal chronic malabsorption disorders, and has also been reported with teenagers suffering from malnutrition exhibiting particular psychiatric diseases. The diagnosis of Gayet-Wernicke's encephalopathy is mainly clinical and is characterized by the triad of mental confusion, occulomotor disorders and ataxia. Treatment consists of vitamin B1 infusion and is generally associated with a good prognosis if the diagnosis is made on time. We report the original observation of a 14-year-old male patient. He was admitted in the child psychiatry unit in the context of anorexia nervosa associated with anxiety disorders. He had been presenting important weight loss and malnutrition for the last eight months. This patient's clinical symptoms consisted of acute anxiety, mental slowness and a progressive confusion that were initially attributed to a psychiatric condition. After the administration of a glucose infusion, the patient developed severe ataxia and a multidirectional nystagmus making the diagnosis of Gayet-Werncike encephalopathy highly probable. Gayet-Wernicke was indeed confirmed by typical ophtalmological and brain MRI findings together with a low blood cell transketolase activity. Symptoms drastically improved after high doses of vitamin B1 infusion. Our case illustrates the importance of timely identification of Gayet-Wernicke encephalopathy in young psychiatric patients particularly when associated with eating disorders. Early vitamin B1 supplementation should be initiated quite early in the diagnosis process to avoid long-term sequels in this young age population. © 2011 Elsevier Masson SAS.SCOPUS: ar.jinfo:eu-repo/semantics/publishe