Derek Ball

In vivo specific tension of human skeletal muscle

In this study, we estimated the specific tensions of soleus (Sol) and tibialis anterior (TA) muscles in six men. Joint moments were measured during maximum voluntary contraction (MVC) and during electrical stimulation. Moment arm lengths and muscle volumes were measured using magnetic resonance imaging, and pennation angles and fascicular lengths were measured using ultrasonography. Tendon and muscle forces were modeled. Two approaches were followed to estimate specific tension. First, muscle moments during electrical stimulation and moment arm lengths, fascicular lengths, and pennation angles during MVC were used (data set A). Then, MVC moments, moment arm lengths at rest, and cadaveric fascicular lengths and pennation angles were used (data set B). The use of data set B yielded the unrealistic specific tension estimates of 104 kN/m(2) in Sol and 658 kN/m(2) in TA. The use of data set A, however, yielded values of 150 and 155 kN/m(2) in Sol and TA, respectively, which agree with in vitro results from fiber type I-predominant muscles. In fact, both Sol and TA are such muscles. Our study demonstrates the feasibility of accurate in vivo estimates of human muscle intrinsic strength.

Muscle oxygen uptake and energy turnover during dynamic exercise at different contraction frequencies in humans

1 It has been established that pulmonary oxygen uptake is greater during cycle exercise in humans at high compared to low contraction frequencies. However, it is unclear whether this is due to more work being performed at the high frequencies and whether the energy turnover of the working muscles is higher. The present study tested the hypothesis that human skeletal muscle oxygen uptake and energy turnover are elevated during exercise at high compared to low contraction frequency when the total power output is the same. 2 Seven subjects performed single‐leg dynamic knee‐extensor exercise for 10 min at contraction frequencies of 60 and 100 r.p.m. where the total power output (comprising the sum of external and internal power output) was matched between frequencies (54 ± 5 vs. 56 ± 5 W; mean ±s.e.m.). Muscle oxygen uptake was determined from measurements of thigh blood flow and femoral arterial–venous differences for oxygen content (a–v O2 diff). Anaerobic energy turnover was estimated from measurements of lactate release and muscle lactate accumulation as well as muscle ATP and phosphocreatine (PCr) utilisation based on analysis of muscle biopsies obtained before and after each exercise bout. 3 Whilst a–v O2 diff was the same between contraction frequencies during exercise, thigh blood flow was higher (P < 0.05) at 100 compared to 60 r.p.m. Thus, muscle V̇O2 was higher (P < 0.05) during exercise at 100 r.p.m. Muscle V̇O2 increased (P < 0.05) by 0.06 ± 0.03 (12 %) and 0.09 ± 0.03 l min−1 (14 %) from the third minute to the end of exercise at 60 and 100 r.p.m., respectively, but there was no difference between the two frequencies. 4 Muscle PCr decreased by 8.1 ± 1.7 and 9.1 ± 2.0 mmol (kg wet wt)−1, and muscle lactate increased to 6.8 ± 2.1 and 9.8 ± 2.5 mmol (kg wet wt)−1 during exercise at 60 and 100 r.p.m., respectively. The total release of lactate during exercise was 48.7 ± 8.8 and 64.3 ± 10.6 mmol at 60 and 100 r.p.m. (not significant, NS). The total anaerobic ATP production was 47 ± 8 and 61 ± 12 mmol kg−1, respectively (NS). 5 Muscle temperature increased (P < 0.05) from 35.8 ± 0.3 to 38.2 ± 0.2 °C at 60 r.p.m. and from 35.9 ± 0.3 to 38.4 ± 0.3 °C at 100 r.p.m. Between 1 and 7 min muscle temperature was higher (P < 0.05) at 100 compared to 60 r.p.m. 6 The estimated mean rate of energy turnover during exercise was higher (P < 0.05) at 100 compared to 60 r.p.m. (238 ± 16 vs. 194 ± 11 J s−1). Thus, mechanical efficiency was lower (P < 0.05) at 100 r.p.m. (24 ± 2 %) compared to 60 r.p.m. (28 ± 3 %). Correspondingly, efficiency expressed as work per mol ATP was lower (P < 0.05) at 100 than at 60 r.p.m. (22.5 ± 2.1 vs. 26.5 ± 2.5 J (mmol ATP)−1). 7 The present study showed that muscle oxygen uptake and energy turnover are elevated during dynamic contractions at a frequency of 100 compared with 60 r.p.m. It was also observed that muscle oxygen uptake increased as exercise progressed in a manner that was not solely related to the increase in muscle temperature and lactate accumulation.

Neuromuscular and hormonal responses to a single session of whole body vibration exercise in healthy young men.

Whole body vibration (WBV) has been proposed as an alternative exercise stimulus to produce adaptive responses similar to resistance exercise. Few studies have analysed acute hormonal responses to WBV.

Does the Human Heart Fatigue Subsequent to Prolonged Exercise

A reduction in left ventricular systolic and diastolic function subsequent to prolonged exercise in healthy humans, often called exercise-induced cardiac fatigue (EICF), has recently been reported in the literature. However, our current understanding of the exact nature and magnitude of EICF is limited. To date, there is no consensus as to the clinical relevance of such findings and whether such alterations in function are likely to impact upon performance. Much of the existing literature has employed field-based competitions. Whilst ecologically valid, this approach has made it difficult to control many factors such as the duration and intensity of effort, fitness and training status of subjects and environmental conditions. The impact of such variables on EICF has not been fully evaluated and is worthy of further research. To date, most EICF studies have been descriptive, with limited success in elucidating mechanisms. To this end, the assessment of humoral markers of cardiac myocyte or membrane disruption has produced contradictory findings partially due to controversy over the validity of specific assays. It is, therefore, important that future research utilises reliable and valid biochemical techniques to address these aetiological factors as well as develop work on other potential contributors to EICF such as elevated free fatty acid concentrations, free radicals and β-adrenoceptor down-regulation. In summary, whilst some descriptive evidence of EICF is available, there are large gaps in our knowledge of what specific factors related to exercise might facilitate functional changes. These topics present interesting but complex challenges to future research in this field.

Diet composition and the performance of high-intensity exercise

The crucial role of muscle glycogen as a fuel during prolonged exercise is well established, and the effects of acute changes in dietary carbohydrate intake on muscle glycogen content and on endurance capacity are equally well known. More recently, it has been recognized that diet can also affect the performance of high-intensity exercise of short (2-7 min) duration. If the muscle glycogen content is lowered by prolonged (1-1.5 h) exhausting cycle exercise, and is subsequently kept low for 3-4 days by consumption of a diet deficient in carbohydrate (< 5% of total energy intake), there is a dramatic (approximately 10-30%) reduction in exercise capacity during cycling sustainable for about 5 min. The same effect is observed if exercise is preceded by 3-4 days on a carbohydrate-restricted diet or by a 24 h total fast without prior depletion of the muscle glycogen. Consumption of a diet high in carbohydrate (70% of total energy intake from carbohydrate) for 3-4 days before exercise improves exercise capacity during high-intensity exercise, although this effect is less consistent. The blood lactate concentration is always lower at the point of fatigue after a diet low in carbohydrate and higher after a diet high in carbohydrate than after a normal diet. Even when the duration of the exercise task is kept constant, the blood lactate concentration is higher after exercise on a diet high in carbohydrate than on a diet low in carbohydrate. Consumption of a low-carbohydrate isoenergetic diet is achieved by an increased intake of protein and fat. A high-protein diet, particularly when combined with a low carbohydrate intake, results in metabolic acidosis, which ensues within 24 h and persists for at least 4 days. This appears to be the result of an increase in the circulating concentrations of strong organic acids, particularly free fatty acids and 3-hydroxybutyrate, together with an increase in the total plasma protein concentration. This acidosis, rather than any decrease in the muscle glycogen content, may be responsible for the reduced exercise capacity in high-intensity exercise; this may be due to a reduced rate of efflux of lactate and hydrogen ions from the working muscles. Alternatively, the accumulation of acetyl groups in the carbohydrate-deprived state may reduce substrate flux through the pyruvate dehydrogenase complex, thus reducing aerobic energy supply and accelerating the onset of fatigue.

Effects of Massage on Limb and Skin Blood Flow after Quadriceps Exercise

PURPOSE At present, there is little scientific evidence that postexercise manual massage has any effect on the factors associated with the recovery process. The purpose of this study was to compare the effects of massage against a resting control condition upon femoral artery blood flow (FABF), skin blood flow (SKBF), skin (SKT), and muscle (MT) temperature after dynamic quadriceps exercise. METHODS Thirteen male volunteers participated in 3 x 2-min bouts of concentric quadriceps exercise followed by 2 x 6-min bouts of deep effleurage and pétrissage massage or a control (rest) period of similar duration in a counterbalanced fashion. Measures of FABF, SKBF, SKT, MT, blood lactate concentration (BLa), heart rate (HR), and blood pressure (BP) were taken at baseline, immediately after exercise, as well as at the midpoint and end of the massage/rest periods. Data were analyzed by two-way ANOVA. RESULTS Significant main effects were found for all variables over time due to effects of exercise. Massage to the quadriceps did not significantly elevate FABF (end-massage 760 +/- 256 vs end-control 733 +/- 161 mL x min(-1)), MT, BL, HR, and BP over control values (P < 0.05). SKBF (end-massage 150 +/- 49 vs end control 6 +/- 4 au) SKT (end-massage 32.2 +/- 0.9 vs end-control 31.1 +/- 1.3degreesC) were elevated after the application of massage compared with the control trial (P < 0.05). CONCLUSION From these data it is proposed that without an increase in arterial blood flow, any increase in SKBF is potentially diverting flow away from recovering muscle. Such a response would question the efficacy of massage as an aid to recovery in postexercise settings.

Human power output during repeated sprint cycle exercise: the influence of thermal stress

Thermal stress is known to impair endurance capacity during moderate prolonged exercise. However, there is relatively little available information concerning the effects of thermal stress on the performance of high-intensity short-duration exercise. The present experiment examined human power output during repeated bouts of short-term maximal exercise. On two separate occasions, seven healthy males performed two 30-s bouts of sprint exercise (sprints I and II), with 4 min of passive recovery in between, on a cycle ergometer. The sprints were performed in both a normal environment [18.7 (1.5)°C, 40 (7)% relative humidity (RH; mean SD)] and a hot environment [30.1 (0.5)°C, 55 (9)% RH]. The order of exercise trials was randomised and separated by a minimum of 4 days. Mean power, peak power and decline in power output were calculated from the flywheel velocity after correction for flywheel acceleration. Peak power output was higher when exercise was performed in the heat compared to the normal environment in both sprint I [910 (172) W vs 656 (58) W; P < 0.01] and sprint II [907 (150) vs 646 (37) W; P < 0.05]. Mean power output was higher in the heat compared to the normal environment in both sprint I [634 (91) W vs 510 (59) W; P < 0.05] and sprint II [589 (70) W vs 482 (47) W; P < 0.05]. There was a faster rate of fatigue (P < 0.05) when exercise was performed in the heat compared to the normal environment. Arterialised-venous blood samples were taken for the determination of acid-base status and blood lactate and blood glucose before exercise, 2 min after sprint I, and at several time points after sprint II. Before exercise there was no difference in resting acid-base status or blood metabolites between environmental conditions. There was a decrease in blood pH, plasma bicarbonate and base excess after sprint I and after sprint II. The degree of post-exercise acidosis was similar when exercise was performed in either of the environmental conditions. The metabolic response to exercise was similar between environmental conditions; the concentration of blood lactate increased (P < 0.01) after sprint I and sprint II but there were no differences in lactate concentration when comparing the exercise bouts performed in a normal and a hot environment. These data demonstrate that when brief intense exercise is performed in the heat, peak power output increases by about 25% and mean power output increases by 15%; this was due to achieving a higher pedal cadence in the heat.

The cardiospecificity of the third-generation cTnT assay after exercise-induced muscle damage.

PURPOSE The purpose of the present study was to examine the cardiospecificity of cTnI and the new third-generation cTnT assay, in the presence of exercise-induced muscle damage in highly trained individuals, and to examine the impact of a maximal-ramping treadmill test on cardiac function. METHODS Eight highly trained male triathletes (mean +/- SD; age: 29 +/- 9 yr; height: 1.79 +/- 0.10 m; body mass: 77 +/- 10 kg; .VO(2max): 67.4 +/- 6.3 mL.kg(-1).min(-1)) completed two bouts of exercise. On the first occasion, subjects completed a maximal-ramping treadmill test. On a separate occasion, the subjects completed 30 min of downhill running (15% gradient) at a speed equivalent to 70% of maximal running velocity attained during the maximal-ramping treadmill test. All subjects were assessed using ECG, echocardiography, and blood analysis. Measurements were taken at rest, immediately after, and 48 h postexercise for each bout of exercise. Echocardiographic analysis was used to determine left ventricular systolic and diastolic function. Blood samples were analyzed for markers of myocyte damage. RESULTS Echocardiographic results indicated normal left ventricular function before and after both exercise bouts. Total CK and CKMB were significantly elevated 48 h after the downhill run. cTnT and cTnI were not elevated at any stage of the study. CONCLUSIONS Neither the maximal-ramping treadmill test nor the 30-min downhill run produced cardiac dysfunction or myocardial damage in young, healthy trained subjects. The elevated total CK and CKMB within the downhill study are noncardiac in origin as demonstrated by the lack of cTnT and cTnI. The cTnI and new third-generation cTnT assays may be used to detect cardiac damage in the presence of elevated total CK and CKMB associated with exercise-induced skeletal muscle damage.

Blood and urine acid–base status of premenopausal omnivorous and vegetarian women

The effect of long-term differences in diet composition on whole-body acid-base status was examined in thirty-three young healthy females. The volunteers were recruited from two separate groups matched approximately for age, height and weight; one group regularly ate meat (omnivores; n 20) and one group did not (vegetarians; n 13). All subjects completed a 7 d weighed intake of food, and from their dietary records, total energy, carbohydrate (CHO), fat and protein content were estimated using computer-based food composition tables. During this week they reported to the laboratory on two occasions, following an overnight fast and separated by at least 48 h. Arterialized venous blood samples were obtained on each visit and these were analysed for blood acid-base status. Haemoglobin and packed cell volume, serum total cholesterol and HDL-cholesterol, serum albumin and total protein were also determined. Two 24 h urine collections were completed; the volume was recorded and samples were analysed for pH, titratable acid and Mg and Ca concentration. Total energy intake of the omnivores was greater (P = 0.0003) than that of the vegetarian group. Dietary intake of CHO (P = 0.024), fat (P = 0.0054) and protein (P = 0.0002) were higher in the omnivorous group than in the vegetarians. There were no differences between the two groups with respect to blood CO2 partial pressure, plasma HCO3- and blood base excess, but blood pH was slightly higher in the omnivores (P = 0.064). Measures of urine acid-base status suggested a lower pH in the omnivore group, but this difference was not statistically significant; a greater titratable acid output was observed with the omnivorous group compared with the vegetarians (48.9 (SE 20.3) v. 35.3 (SE 23.3) mEq/24h; P = 0.018). Although the dietary intake of Ca was not different between the two groups, urinary Ca excretion of the omnivores was significantly higher (3.87 (SD 1.34) v. 3.22 (SD 1.20) mmol/24 h) than that of the vegetarians (P = 0.014). It is suggested that the higher protein intake of the omnivores resulted in an increase in urinary total acid excretion, which may explain the higher rate of Ca excretion.

Using systems biology to define the essential biological networks responsible for adaptation to endurance exercise training

We predict that RNA level regulation is as diverse and powerful as protein level regulation when considering physiological adaptation. Non-coding RNA molecules, such as miRNAs (microRNAs), have emerged as a powerful mechanism for post-transcriptional regulation of mRNA. In an effort to define the role of miRNA in human skeletal-muscle biology, we have initiated profiling of muscle RNA before and after endurance exercise training. The robust molecular phenotype of muscle is established using unbiased analysis strategies of the raw data, reflecting the statistical power of gene ontology and network analysis. We can thus determine the structural features of the skeletal-muscle transcriptome, identify discrete networks activated by training and utilize bioinformatics predictions to establish the interaction between non-coding RNA modulation and Affymetrix expression profiles.