McArdle disease: a unique study model in sports medicine

McArdle disease is arguably the paradigm of exercise intolerance in humans. This disorder is caused by inherited deficiency of myophosphorylase, the enzyme isoform that initiates glycogen breakdown in skeletal muscles. Because patients are unable to obtain energy from their muscle glycogen stores, this disease provides an interesting model of study for exercise physiologists, allowing insight to be gained into the understanding of glycogen-dependent muscle functions. Of special interest in the field of muscle physiology and sports medicine are also some specific (if not unique) characteristics of this disorder, such as the so-called 'second wind' phenomenon, the frequent exercise-induced rhabdomyolysis and myoglobinuria episodes suffered by patients (with muscle damage also occurring under basal conditions), or the early appearance of fatigue and contractures, among others. In this article we review the main pathophysiological features of this disorder leading to exercise intolerance as well as the currently available therapeutic possibilities.

Influence of fat percentage, front thigh skinfold and girth on the maximum radial displacement of the dominant rectus femoris

4.171 JCR (2013) Q1, 6/81 Sport sciences

Time for doctors to practise what they preach and preach what they practise

SIN FINANCIACIÓN

Validity of the physical activity questionnaires IPAQ-SF and GPAQ for Cancer Survivors: Insights from a Spanish cohort

Regular physical activity (PA) decreases mortality risk in survivors of breast and colorectal cancer. Such impacts of exercise have prompted initiatives designed both to promote and adequately monitor PA in cancer survivors. This study examines the validity of 2 widely used self-report methods for PA determination, the International Physical Activity Questionnaire short version (IPAQ-SF) and Global Physical Activity Questionnaire (GPAQ). Both instruments were compared with the triaxial accelerometry (Actigraph) method as an objective reference standard. Study participants were 204 cancer survivors (both sexes, aged 18-79 years). Compared with accelerometry, both questionnaires significantly overestimated PA levels (across all intensities) and underestimated physical inactivity levels. No differences were detected between the 2 questionnaires except for a shorter inactivity time estimated by GPAQ (p=0.001). The Bland and Altman method confirmed that both questionnaires overestimated all PA levels. Receiver operating characteristic (ROC) analysis classified IPAQ and GPAQ as fair and poor predictors, respectively, of the proportions of survivors fulfilling international PA recommendations (≥150 min·week-1 of moderate-vigorous PA). IPAQ-SF showed a higher sensitivity but lower specificity than GPAQ. Our data do not support the use of IPAQ-SF or GPAQ to determine PA or inactivity levels in cancer survivors.

Analysis of the aerobic-anaerobic transition in elite cyclists during incremental exercise with the use of electromyography

To investigate the validity and reliability of surface electromyography (EMG) as a new non-invasive determinant of the metabolic response to incremental exercise in elite cyclists. The relation between EMG activity and other more conventional methods for analysing the aerobic-anaerobic transition such as blood lactate measurements (lactate threshold (LT) and onset of blood lactate accumulation (OBLA)) and ventilatory parameters (ventilatory thresholds 1 and 2 (VT1 and VT2)) was studied.Twenty eight elite road cyclists (age 24 (4) years; VO2MAX 69.9 (6.4) ml/kg/min; values mean (SD)) were selected as subjects. Each of them performed a ramp protocol (starting at 0 W, with increases of 5 W every 12 seconds) on a cycle ergometer (validity study). In addition, 15 of them performed the same test twice (reliability study). During the tests, data on gas exchange and blood lactate levels were collected to determine VT1, VT2, LT, and OBLA. The root mean squares of EMG signals (rms-EMG) were recorded from both the vastus lateralis and the rectus femoris at each intensity using surface electrodes. Results - A two threshold response was detected in the rms-EMG recordings from both muscles in 90% of subjects, with two breakpoints, EMG(T1) and EMG(T2), at around 60-70% and 80-90% of VO2MAX respectively. The results of the reliability study showed no significant differences (p > 0.05) between mean values of EMG(T1) and EMG(T2) obtained in both tests. Furthermore, no significant differences (p > 0.05) existed between mean values of EMG(T1), in the vastus lateralis and rectus femoris, and VT1 and LT (62.8 (14.5) and 69.0 (6.2) and 64.6 (6.4) and 68.7 (8.2)% of VO2MAX respectively), or between mean values of EMG(T2), in the vastus lateralis and rectus femoris, and VT2 and OBLA (86.9 (9.0) and 88.0 (6.2) and 84.6 (6.5) and 87.7 (6.4)% of VO2MAX respectively). Rms-EMG may be a useful complementary non-invasive method for analysing the aerobic-anaerobic transition (ventilatory and lactate thresholds) in elite cyclists.

Heart dimensions may influence the occurrence of the heart rate deflection point in highly trained cyclists

To determine whether the heart rate (HR) response to exercise in 21 highly trained cyclists (mean (SD) age 25 (3) years) was related to their heart dimensions. Methods—Before performing an incremental exercise test involving a ramp protocol with workload increases of 25 W/min, each subject underwent echocardiographic evaluation of the following variables: left ventricular end diastolic internal diameter (LVIDd), left ventricular posterior wall thickness at end diastole (LVPWTd), interventricular septal wall thickness at end diastole (IVSTd), left ventricular mass index (LVMI), left atrial dimension (LAD), longitudinal left atrial (LLAD) and right atrial (LRAD) dimensions, and the ratio of early to late (E/A) diastolic flow velocity. Results—The HR response showed a de- flection point (HRd) at about 85% V~ O2MAX in 66.7% of subjects (D group; n = 14) and was linear in 33.3% (NoD group; n = 7). Several echocardiographic variables (LVMI, LAD, LLAD, LRAD) indicative of heart dimensions were similar in each group. However, mean LPWTd (p<0.01) and IVSTd (p<0.05) values were signifi- cantly higher in the D group. Finally, no significant diVerence between groups was found with respect to the E/A. The HR response is curvilinear during incremental exercise in a considerable number of highly trained endurance athletes—that is, top level cyclists. The departure of HR increase from linearity may predominantly occur in athletes with thicker heart walls.

Trace elements and electrolytes in human resting mixed saliva after exercise

Objectives—Exercise is known to cause changes in the concentration of salivary components such as amylase, Na, and Cl. The aim of this investigation was to evaluate the eVect of physical exercise on the levels of trace elements and electrolytes in whole (mixed) saliva. Methods—Forty subjects performed a maximal exercise test on a cycle ergometer. Samples of saliva were obtained before and immediately after the exercise test. Sample concentrations of Fe, Mg, Sc, Cr, Mn, Co, Cu, Zn, Se, Sr, Ag, Sb, Cs, and Hg were determined by inductively coupled plasma mass spectrometry and concentrations of Ca and Na by atomic absorption spectrometry. Results—After exercise, Mg and Na levels showed a significant increase (p<0.05) while Mn levels fell (p<0.05). Zn/Cu molar ratios were unaVected by exercise. Conclusions—Intense physical exercise induced changes in the concentrations of only three (Na, Mg, and Mn) of the 16 elements analysed in the saliva samples. Further research is needed to assess the clinical implications of these findings.