Alfredo Santalla

In professional road cyclists, low pedaling cadences are less efficient.

PURPOSE To determine the effects of changes in pedaling frequency on the gross efficiency (GE) and other physiological variables (oxygen uptake (VO2), HR, lactate, pH, ventilation, motor unit recruitment estimated by EMG) of professional cyclists while generating high power outputs (PO). METHODS Following a counterbalanced, cross-over design, eight professional cyclists (age (mean +/- SD): 26 +/- 2 yr, VO2max: 74.0 +/- 5.7 mL x kg x min) performed three 6-min bouts at a fixed PO (mean of 366 +/- 37 W) and at a cadence of 60, 80, and 100 rpm. RESULTS Values of GE averaged 22.4 +/- 1.7, 23.6 +/- 1.8 and 24.2 +/- 2.0% at 60, 80, and 100 rpm, respectively. Mean GE at 100 rpm was significantly higher than at 60 rpm (P < 0.05). Similarly, mean values of VO2, HR, rates of perceived exertion (RPE), lactate and normalized root-mean square EMG (rms-EMG) in both vastus lateralis and gluteus maximum muscles decreased at increasing cadences. CONCLUSIONS In professional road cyclists riding at high PO, GE/economy improves at increasing pedaling cadences.

Kinetics of VO(2) in professional cyclists.

PURPOSE To analyze the kinetics of oxygen uptake (VO(2)) in professional road cyclists during a ramp cycle ergometer test and to compare the results with those derived from well-trained amateur cyclists. METHODS Twelve professional cyclists (P group; 25 +/- 1 yr; maximal power output (W(max)), 508.3 +/- 9.3 watts) and 10 amateur cyclists (A group; 22 +/- 1 y; W(max), 429.9 +/- 8.6 watts) performed a ramp test until exhaustion (power output increases of 25 watts x min(-1)). The regression lines of the VO(2):power output (W) relationship were calculated for the following three phases: phase I (below the lactate threshold (LT)), phase II (between LT and the respiratory compensation point (RCP)), and phase III (above RCP). RESULTS In group P, the mean slope (Delta VO(2):Delta W) of the VO(2):W relationship decreased significantly (P < 0.01) across the three phases (9.9 +/- 0.1, 8.9 +/- 0.2, and 3.8 +/- 0.6 mL O(2) x watts(-1) x min(-1) for phases I, II, and III, respectively). No significant differences (P > 0.05) were found between phases I and II (P > 0.05) in group A, whereas Delta VO(2):Delta W significantly increased in phase III (P < 0.01), compared with phase II (10.2 +/- 0.3, 9.2 +/- 0.4, and 10.1 +/- 1.1 mL O(2) x watts(-1) x min(-1) in phases I, II, and III, respectively). The mean value of Delta VO(2):Delta W for phase III was significantly lower in group P than in group A (P < 0.01). CONCLUSION Contrary to the case in amateur riders, the rise in VO(2) in professional cyclists is attenuated at moderate to high workloads. This is possibly an adaptation to the higher demands of their training/competition schedule.

Sodium bicarbonate ingestion does not alter the slow component of oxygen uptake kinetics in professional cyclists.

We examined the effects of pre-exercise sodium bicarbonate (NaHCO3) ingestion on the slow component of oxygen uptake (VO2) kinetics in seven professional road cyclists during intense exercise. One hour after ingesting either a placebo or NaHCO3 (0.3 g x kg body mass(-1)), each cyclist (age, 25 +/- 2 years; VO2max, 74.7 +/- 5.9 ml x kg(-1) x min(-1); mean +/- s) performed two bouts of 6 min duration at an intensity of 90% VO2max interspersed by 8 min of active recovery. Gas exchange and blood data (pH, blood lactate concentration and [HCO3-]) were collected during the tests. In both bouts, the slow component of VO2 was defined as the difference between end-exercise VO2 and the VO2 at the end of the third minute. No significant difference was found in the slow component of VO2 between conditions in the first (NaHCO3, 210 +/- 69 ml; placebo, 239 +/- 105 ml) or second trial (NaHCO3, 123 +/- 88 ml; placebo, 197 +/- 101 ml). In conclusion, pre-exercise NaHCO3 ingestion did not significantly attenuate the VO2 slow component of professional road cyclists during high-intensity exercise.

McArdle Disease: Update of Reported Mutations and Polymorphisms in the PYGM Gene

McArdle disease is an autosomal‐recessive disorder caused by inherited deficiency of the muscle isoform of glycogen phosphorylase (or “myophosphorylase”), which catalyzes the first step of glycogen catabolism, releasing glucose‐1‐phosphate from glycogen deposits. As a result, muscle metabolism is impaired, leading to different degrees of exercise intolerance. Patients range from asymptomatic to severely affected, including in some cases, limitations in activities of daily living. The PYGM gene codifies myophosphoylase and to date 147 pathogenic mutations and 39 polymorphisms have been reported. Exon 1 and 17 are mutational hot‐spots in PYGM and 50% of the described mutations are missense. However, c.148C>T (commonly known as p.R50X) is the most frequent mutation in the majority of the studied populations. No genotype–phenotype correlation has been reported and no mutations have been described in the myophosphorylase domains affecting the phosphorylated Ser‐15, the 280s loop, the pyridoxal 5′‐phosphate, and the nucleoside inhibitor binding sites. A newly generated knock‐in mouse model is now available, which renders the main clinical and molecular features of the disease. Well‐established methods for diagnosing patients in laboratories around the world will shorten the frequent ∼20‐year period stretching from first symptoms appearance to the genetic diagnosis.

Feasibility of resistance training in adult McArdle patients: clinical outcomes and muscle strength and mass benefits

We analyzed the effects of a 4-month resistance (weight lifting) training program followed by a 2-month detraining period in 7 adult McArdle patients (5 female) on: muscle mass (assessed by DXA), strength, serum creatine kinase (CK) activity and clinical severity. Adherence to training was ≥84% in all patients and no major contraindication or side effect was noted during the training or strength assessment sessions. The training program had a significant impact on total and lower extremities’ lean mass (P < 0.05 for the time effect), with mean values increasing with training by +855 g (95% confidence interval (CI): 30, 1679) and +547 g (95%CI: 116, 978), respectively, and significantly decreasing with detraining. Body fat showed no significant changes over the study period. Bench press and half-squat performance, expressed as the highest value of average muscle power (W) or force (N) in the concentric-repetition phase of both tests showed a consistent increase over the 4-month training period, and decreased with detraining. Yet muscle strength and power detraining values were significantly higher than pre-training values, indicating that a training effect was still present after detraining. Importantly, all the participants, with no exception, showed a clear gain in muscle strength after the 4-month training period, e.g., bench press: +52 W (95% CI: 13, 91); half-squat: +173 W (95% CI: 96, 251). No significant time effect (P > 0.05) was noted for baseline or post strength assessment values of serum CK activity, which remained essentially within the range reported in our laboratory for McArdle patients. All the patients changed to a lower severity class with training, such that none of them were in the highest disease severity class (3) after the intervention and, as such, they did not have fixed muscle weakness after training. Clinical improvements were retained, in all but one patient, after detraining, such that after detraining all patients were classed as class 1 for disease severity.

Muscle Efficiency Improves over Time in World-Class Cyclists

PURPOSE To determine the change in muscular efficiency in world-class professional cyclists during years of training/competition. METHODS Twelve male world-class professional road cyclists (mean +/- SD: age = 22.6 +/- 3.8 yr and VO(2max) = 75.5 +/- 3.3 mL x kg(-1) x min(-1)) performed an incremental test (starting at 100 W with workload increases of 50 W every 4-min interval until volitional exhaustion) before and after a five-season period. Delta efficiency (DE) was calculated from 100 W to that power output (PO) in which the RER was 1. RESULTS DE increased (P < 0.01) from 23.61 +/- 2.78% to 26.97 +/- 3.7% from the first to the fifth year, whereas VO(2max) showed no significant increase. A significant inverse correlation (r = -0.620; P = 0.032) between DE and VO(2max) (mL x kg(-1) x min(-1)) was found in the fifth year, whereas no significant correlation between these variables was found in the first year. A significant inverse correlation (r = -0.63; P = 0.029) was found between the increase percentage in DE (DeltaDE) and VO(2max) (mL x kg(-1) x min(-1)) in the fifth year, whereas no significant correlation was found between these variables in the first year. CONCLUSION The results show an increase in DE in world-class professional cyclists during a five-season training/competition period, without significant variations in VO(2max). The results also suggest that the increase in DE could be a possible way for performance compensation, especially in those subjects with lower VO(2max).

Lactic acidosis, potassium, and the heart rate deflection point in professional road cyclists

Objective: To determine the influence of lactic acidosis, the Bohr effect, and exercise induced hyperkalaemia on the occurrence of the heart rate deflection point (HRDP) in elite (professional) cyclists. Methods: Sixteen professional male road cyclists (mean (SD) age 26 (1) years) performed a ramp test on a cycle ergometer (workload increases of 5 W/12 s, averaging 25 W/min). Heart rate (HR), gas exchange parameters, and blood variables (lactate, pH, P50 of the oxyhaemoglobin dissociation curve, and K+) were measured during the tests. Results: A HRDP was shown in 56% of subjects at about 88% of their maximal HR (HRDP group; n = 9) but was linear in the rest (No-HRDP group; n = 7). In the HRDP group, the slope of the HR-workload regression line above the HRDP correlated inversely with levels of K+ at the maximal power output (r = −0.67; p<0.05). Conclusions: The HRDP phenomenon is associated, at least partly, with exercise induced hyperkalaemia.

Effects of electrical stimulation on Vo2 kinetics and delta efficiency in healthy young men

Objective: To determine the effects of electrical stimulation (ES) on oxygen uptake (Vo2) kinetics and delta efficiency (DE) during gradual exercise. The hypothesis was that ES would attenuate the Vo2-workload relation and improve DE. Methods: Fifteen healthy, untrained men (mean (SD) age 22 (5) years) were selected. Ten were electrostimulated on both quadriceps muscles with a frequency of 45–60 Hz, with 12 seconds of stimulation followed by eight seconds recovery for a total of 30 minutes a day, three days a week for six weeks. The remaining five subjects were assigned to a control group. A standardised exercise test on a cycle ergometer (ramp protocol, workload increases of 20 W/min) was performed by each subject before and after the experimental period. The slope of the Vo2-power output (W) relation (ΔVo2/ΔW) and DE were calculated in each subject at moderate to high intensities (above the ventilatory threshold—that is, from 50–60% to 100% Vo2max). Results: The mean (SEM) values for ΔVo2/ΔW and DE had significantly decreased and increased respectively after the six week ES programme (p<0.05; 9.8 (0.2) v 8.6 (0.5) ml O2/W/min respectively and 27.7 (0.9) v 31.5 (1.4)% respectively). Conclusions: ES could be used as a supplementary tool to improve two of the main determinants of endurance capacity, namely Vo2 kinetics and work efficiency.

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. Patients have been traditionally advised by clinicians to refrain from exercise, yet sports medicine and careful exercise prescription are their best allies at present because no effective enzyme replacement therapy is expected to be available in the near future. As of today, although unable to restore myophosphorylase deficiency, the ‘simple’ use of exercise as therapy seems probably more promising and practical for patients than more ‘complex’ medical approaches.

Cardiorespiratory fitness, physical activity, and quality of life in patients with McArdle disease

BACKGROUND This study sought to determine whether health-related quality of life (HRQoL) could be related to cardiorespiratory fitness (CRF) and/or physical activity (PA) in patients with McArdle disease and to compare the CRF and HRQoL data obtained with normative data for age- and sex-matched healthy subjects. METHODS Eighty-one adult patients with McArdle disease underwent aerobic capacity testing to determine peak oxygen uptake (V˙O2peak), among other variables. HRQoL (Short Form 36-Item Health Survey questionnaire version 2 (SF-36 version 2)) and PA (International Physical Activity Questionnaire) questionnaires were completed by 45 of the patients. HRQoL and V˙O2peak data were compared with published normative data. RESULTS Positive correlations were observed between V˙O2peak and leisure time PA versus the physical component summary score and scores for several domains of the SF-36 questionnaire after adjusting for age, body mass index, and disease severity (R values, 0.42-0.68; all P < 0.01). In a regression analysis, the physical component summary score was directly linked to V˙O2peak (B = 1.28; 95% confidence interval, 0.78-1.78; P < 0.001; R = 0.422). The mean V˙O2peak recorded for patients with McArdle disease was 57% lower than the normative value (17.1 ± 5.3 vs 40.0 ± 9.5 mL·kg·min, respectively; P < 0.001). All patients showed a CRF below their age-/sex-matched normality value and scored clinically lower in the physical component summary and in most SF-36 domains compared with the Spanish general population. CONCLUSIONS Patients showed a consistent link between higher physical HRQoL scores and higher CRF. Patients fulfilling leisure time PA recommendations showed higher CRF and physical HRQoL scores than those not meeting guideline recommendations. According to normative data for healthy subjects, CRF and physical HRQoL are severely impaired in adult patients with McArdle disease.