Risk Factors for Knee Injury in Golf: A Systematic Review.

BACKGROUND: Golf is commonly considered a low-impact sport that carries little risk of injury to the knee and is generally allowed following total knee arthroplasty (TKA). Kinematic and kinetic studies of the golf swing have reported results relevant to the knee, but consensus as to the loads experienced during a swing and how the biomechanics of an individual's technique may expose the knee to risk of injury is lacking. OBJECTIVES: Our objective was to establish (1) the prevalence of knee injury resulting from participation in golf and (2) the risk factors for knee injury from a biomechanical perspective, based on an improved understanding of the internal loading conditions and kinematics that occur in the knee from the time of addressing the ball to the end of the follow-through. METHODS: A systematic literature search was conducted to determine the injury rate, kinematic patterns, loading, and muscle activity of the knee during golf. RESULTS: A knee injury prevalence of 3-18% was established among both professional and amateur players, with no clear dependence on skill level or sex; however, older players appear at greater risk of injury. Studies reporting kinematics indicate that the lead knee is exposed to a complex series of motions involving rapid extension and large magnitudes of tibial internal rotation, conditions that may pose risks to the structures of a natural knee or TKA. To date, the loads experienced by the lead knee during a golf swing have been reported inconsistently in the literature. Compressive loads ranging from 100 to 440% bodyweight have been calculated and measured using methods including inverse dynamics analysis and instrumented knee implants. Additionally, the magnitude of loading appears to be independent of the club used. CONCLUSIONS: This review is the first to highlight the lack of consensus regarding knee loading during the golf swing and the associated risks of injury. Results from the literature suggest the lead knee is subject to a higher magnitude of stress and more demanding motions than the trail knee. Therefore, recommendations regarding return to golf following knee injury or surgical intervention should carefully consider the laterality of the injury.

Respiratory muscle training improves respiratory muscle endurance but not exercise tolerance in children with cystic fibrosis.

BACKGROUND: Respiratory muscle endurance (RME) training has been shown to increase exercise endurance and lung function in adults with cystic fibrosis (CF). We conducted an interventional study to investigate the effectiveness of RME training on CF-related health outcomes in children. METHODS: In a crossover trial, 22 children, aged 9-18 years, with CF performed 8 weeks of RME training and standard chest physiotherapy in a randomized sequence separated by a 1 week washout period. All children underwent training sessions using the RME training device before beginning the study. The primary outcomes were RME (in minutes) and exercise endurance (in minutes). Data were analyzed according to the intention-to-treat principle. RESULTS: Sixteen of 22 children (73%) completed the study. Study dropouts tended to be older with more advanced lung disease. After RME training, respiratory muscle endurance significantly increased by 7.03 ± 8.15 min (mean ± standard deviation, P < 0.001), whereas exercise endurance was unchanged by RME training (0.80 ± 2.58 min, P = 0.169). No significant improvement in secondary outcomes (lung function, CF quality of life, and CF clinical score) were observed. The small sample size and short intervention time have to be acknowledged as limitations of our study. CONCLUSIONS: RME training led to a significant increase in respiratory muscle endurance in children with CF. However, RME training did not improve exercise endurance or other CF-related health outcomes. Thus, our results do not support the routine use of RME training in the care of children with CF. Future studies in larger populations and with prolonged intervention time may overcome the limitations of our study. Pediatr Pulmonol. 2017;52:331-336. © 2017 Wiley Periodicals, Inc.

Effect of Regular Yoga Practice on Respiratory Regulation and Exercise Performance.

Yoga alters spontaneous respiratory regulation and reduces hypoxic and hypercapnic ventilatory responses. Since a lower ventilatory response is associated with an improved endurance capacity during whole-body exercise, we tested whether yogic subjects (YOGA) show an increased endurance capacity compared to matched non-yogic individuals (CON) with similar physical activity levels. Resting ventilation, the ventilatory response to hypercapnia, passive leg movement and exercise, as well as endurance performance were assessed. YOGA (n = 9), compared to CONTROL (n = 6), had a higher tidal volume at rest (0.7±0.2 vs. 0.5±0.1 l, p = 0.034) and a reduced ventilatory response to hypercapnia (33±15 vs. 47±15 l·min(-1), p = 0.048). A YOGA subgroup (n = 6) with maximal performance similar to CONTROL showed a blunted ventilatory response to passive cycling (11±2 vs. 14±2 l·min(-1), p = 0.039) and a tendency towards lower exercise ventilation (33±2 vs. 36±3 l·min(-1), p = 0.094) while cycling endurance (YOGA: 17.3±3.3; CON: 19.6±8.5 min, p = 0.276) did not differ. Thus, yoga practice was not associated with improved exercise capacity nor with significant changes in exercise ventilation despite a significantly different respiratory regulation at rest and in response to hypercapnia and passive leg movement.

RhEPO improves time to exhaustion by non-hematopoietic factors in humans.

PURPOSE: Erythropoietin (EPO) controls red cell volume (RCV) and plasma volume (PV). Therefore, injecting recombinant human EPO (rhEPO) increases RCV and most likely reduces PV. RhEPO-induced endurance improvements are explained by an increase in blood oxygen (O2) transport capacity, which increases maximum O2 uptake ([Formula: see text]O2max). However, it is debatable whether increased RCV or [Formula: see text]O2max are the main reasons for the prolongation of the time to exhaustion (t lim) at submaximal intensity. We hypothesized that high rhEPO doses in particular contracts PV such that the improvement in t lim is not as strong as at lower doses while [Formula: see text]O2max increases in a dose-dependent manner. METHODS: We investigated the effects of different doses of rhEPO given during 4 weeks [placebo (P), low (L), medium (M), and high (H) dosage] on RCV, PV, [Formula: see text]O2max and t lim in 40 subjects. RESULTS: While RCV increased in a dose-dependent manner, PV decreased independent of the rhEPO dose. The improvements in t lim (P +21.4 ± 23.8%; L +16.7 ± 29.8%; M +44.8 ± 62.7%; H +69.7 ± 73.4%) depended on the applied doses (R (2) = 0.89) and clearly exceeded the dose-independent [Formula: see text]O2max increases (P -1.7 ± 3.2%; L +2.6 ± 6.8%; M +5.7 ± 5.1 %; H +5.6 ± 4.3 %) after 4 weeks of rhEPO administration. Furthermore, the absolute t lim was not related (R (2) ≈ 0) to RCV or to [Formula: see text]O2max. CONCLUSIONS: We conclude that a contraction in PV does not negatively affect t lim and that rhEPO improves t lim by additional, non-hematopoietic factors.

One bout of vibration exercise with vascular occlusion activates satellite cells.

NEW FINDINGS: What is the central question of this study? Acute skeletal muscle satellite cell (SC) activation is associated with skeletal muscle hypertrophy. Although the quantity of SCs has been reported to increase following a single bout of resistance exercise, data on muscle fibre type-specific SC quantity and/or activation status after a single bout of vibration is presently lacking. What is the main finding and its importance? By determining SCs from muscle biopsies of the vastus lateralis using immunohistochemistry, we conclude that modification of vibration exercise by superimposition of occlusion induced activation and differentiation of SCs in young men, which had not been observed with whole-body vibration or blood flow restriction alone. We tested the hypothesis that whole-body vibration (WBV) is insufficient to expand satellite cell numbers 24 h postexercise, whereas WBV in combination with blood flow restriction (BFR) is sufficient. Twenty-five young men were randomly assigned to one of the following three groups: WBV, BFR exercise or WBVBFR. Satellite cell numbers were determined from muscle biopsies of the vastus lateralis muscle using immunohistochemistry. Satellite cell quantity and frequency (+99.4%, P = 0.012 and +77.1%, P = 0.010, respectively) increased only in the WBVBFR group. Similar results were obtained for the quantity and frequency of myogenin-positive myonuclei (+139.0%, P < 0.001 and +148.4%, P < 0.001, respectively). We conclude that modification of WBV by superimposition of BFR induced activation and differentiation of satellite cells in young men, which had not been observed with WBV or BFR alone. These data suggest that WBVBFR might represent a novel viable anabolic stimulus.

Reduced Bone Strength and Muscle Force in Women 27 Years After Anorexia Nervosa.

CONTEXT: A substantial body of research findings indicate that muscle mass and bone mass are reduced in populations of anorexic females, even in such populations whose anorexia nervosa had been in remission for longer periods. OBJECTIVE: This study aimed to investigate whether the bone of an anorexia nervosa recovery cohort is adapted to maximal muscle forces and whether there are alterations in the structure of the tibia in this population, as compared with a control group. DESIGN, SETTING, AND PARTICIPANTS: This was a cross-sectional study of 22 women in Switzerland who have remained in stable recovery from anorexia nervosa for an average of 27 years. The measurements were compared with those of an age- and gender-matched control group (n = 73). INTERVENTIONS: There were no interventions. MAIN OUTCOME MEASURES: Bone characteristics of the tibia and maximal voluntary ground reaction force (Fm1LH) were measured. RESULTS: The variability in volumetric bone mineral content (vBMC) at the 14% site was explained by 54.7% on the grounds of Fm1LH (P < .001). Formerly anorexic women had an 11.6% lower Fm1LH (P = .001), a significantly lower vBMC at 4% and 14% of tibia length, and an 11.9% (P = .001) lower body mass than the age- and gender-matched control population. Present body mass of the anorexia group correlated positively with vBMC at the 14% site (P < .001). CONCLUSIONS: Despite the fact that findings reflected an adaptation of bone to the acting forces, most results indicated that the test cohort generally suffered from a secondary bone defect. In addition, maximal muscle force was also impaired in the formerly anorexic women.

High-intensity interval training with vibration as rest intervals attenuates fiber atrophy and prevents decreases in anaerobic performance.

UNLABELLED: Aerobic high-intensity interval training (HIT) improves cardiovascular capacity but may reduce the finite work capacity above critical power (W') and lead to atrophy of myosin heavy chain (MyHC)-2 fibers. Since whole-body vibration may enhance indices of anaerobic performance, we examined whether side-alternating whole-body vibration as a replacement for the active rest intervals during a 4 x 4 min HIT prevents decreases in anaerobic performance and capacity without compromising gains in aerobic function. Thirty-three young recreationally active men were randomly assigned to conduct either conventional 4 x 4 min HIT, HIT with 3 min of WBV at 18 Hz (HIT+VIB18) or 30 Hz (HIT+VIB30) in lieu of conventional rest intervals, or WBV at 30 Hz (VIB30). Pre and post training, critical power (CP), W', cellular muscle characteristics, as well as cardiovascular and neuromuscular variables were determined. W' (-14.3%, P = 0.013), maximal voluntary torque (-8.6%, P = 0.001), rate of force development (-10.5%, P = 0.018), maximal jumping power (-6.3%, P = 0.007) and cross-sectional areas of MyHC-2A fibers (-6.4%, P = 0.044) were reduced only after conventional HIT. CP, V̇O2peak, peak cardiac output, and overall capillary-to-fiber ratio were increased after HIT, HIT+VIB18, and HIT+VIB30 without differences between groups. HIT-specific reductions in anaerobic performance and capacity were prevented by replacing active rest intervals with side-alternating whole-body vibration, notably without compromising aerobic adaptations. Therefore, competitive cyclists (and potentially other endurance-oriented athletes) may benefit from replacing the active rest intervals during aerobic HIT with side-alternating whole-body vibration. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01875146.

High-load resistance exercise with superimposed vibration and vascular occlusion increases critical power, capillaries and lean mass in endurance-trained men.

PURPOSE: It is a widely accepted premise in the scientific community and by athletes alike, that adding resistance exercise to a regular regimen of endurance training increases endurance performance in endurance-trained men. However, critical power (CP), capillarization, and myofiber size remain unaffected by this addition. Therefore, we tested whether the superimposition of resistance exercise with whole-body vibration and vascular occlusion (vibroX) would improve these variables in endurance-trained males relative to resistance exercise alone. METHODS: Twenty-one young, endurance-trained males were randomly assigned either to a vibroX (n = 11) or resistance (n = 10) training group. Both groups trained in a progressive mode twice a week for 8 weeks. Pre and post training, histochemical muscle characteristics, thigh muscle size, endurance and strength parameters were determined. RESULTS: vibroX increased CP (P = 0.001), overall capillary-to-fiber ratio (P = 0.001) and thigh lean mass (P < 0.001), while these parameters were unaffected by resistance training. The gain in CP by vibroX was positively correlated with the gain in capillarization (R(2) = 0.605, P = 0.008), and the gain in thigh lean mass was paralleled by increases in MyHC-1 and MyHC-2 fiber cross-sectional areas and strength. Maximum voluntary torque and the finite work capacity above CP (W') increased significantly only following resistance training. CONCLUSIONS: We achieved a proof of concept by demonstrating that modification of resistance exercise by superimposing side-alternating whole-body vibration and sustained vascular occlusion induced further improvements in CP, capillarization and hypertrophy, all of which were not observed with resistance training alone.

Optimised heart rate formulae to monitor endurance training in sedentary individuals.

The aim of this study was to assess the validity of the heart rate formula 170 - 0.5 age ± 10 used to prescribe endurance training for healthy sedentary or moderately trained individuals. A total of 795 incremental tests of women and men during running and cycling were analysed. The maximum heart rate, heart rate at deflection and age-dependent declines of these heart rates were determined. The maximum heart rate and the heart rate at deflection were greater during running (women: 192 ± 10 and 181 ± 9 bpm; men: 191 ± 10 and 179 ± 10 bpm) than cycling (women: 185 ± 11 and 170 ± 11 bpm; men: 187 ± 10 and 169 ± 11 bpm, P < 0.001) without any sex-based difference. With the upper limit of the existing heart rate formula, 4% during running and 35% during cycling exceeded the heart rate at deflection. We suggest two heart rate formulae for healthy sedentary or moderately endurance trained individuals separated for mode of exercise but not for sex: 165 - 0.5 age ± 5 for running and 160 - 0.5 age ± 5 for cycling.

Multiday acute sodium bicarbonate intake improves endurance capacity and reduces acidosis in men.

BACKGROUND: The purpose was to investigate the effects of one dose of NaHCO3 per day for five consecutive days on cycling time-to-exhaustion (Tlim) at 'Critical Power' (CP) and acid-base parameters in endurance athletes. METHODS: Eight trained male cyclists and triathletes completed two exercise periods in a randomized, placebo-controlled, double-blind interventional crossover investigation. Before each period, CP was determined. Afterwards, participants completed five constant-load cycling trials at CP until volitional exhaustion on five consecutive days, either after a dose of NaHCO3 (0.3 g·kg-1 body mass) or placebo (0.045 g·kg-1 body mass NaCl). RESULTS: Average Tlim increased by 23.5% with NaHCO3 supplementation as compared to placebo (826.5 ± 180.1 vs. 669.0 ± 167.2 s; P = 0.001). However, there was no time effect for Tlim (P = 0.375). [HCO3-] showed a main effect for condition (NaHCO3: 32.5 ± 2.2 mmol·l-1; placebo: 26.2 ± 1.4 mmol·l-1; P < 0.001) but not for time (P = 0.835). NaHCO3 supplementation resulted in an expansion of plasma volume relative to placebo (P = 0.003). CONCLUSIONS: The increase in Tlim was accompanied by an increase in [HCO3-], suggesting that acidosis might be a limiting factor for exercise at CP. Prolonged NaHCO3 supplementation did not lead to a further increase in [HCO3-] due to the concurrent elevation in plasma volume. This may explain why Tlim remained unaltered despite the prolonged NaHCO3 supplementation period. Ingestion of one single NaHCO3 dose per day before the competition during multiday competitions or tournaments might be a valuable strategy for performance enhancement. TRIAL REGISTRATION: Trial registration: ClinicalTrials.gov Identifier NCT01621074.

Combined whole-body vibration, resistance exercise, and sustained vascular occlusion increases PGC-1α and VEGF mRNA abundances.

We previously reported that high load resistance exercise with superimposed whole-body vibration and sustained vascular occlusion (vibroX) markedly improves cycling endurance capacity, increases capillary-to-fibre ratio and skeletal muscle oxidative enzyme activity in untrained young women. These findings are intriguing, since increases in oxidative muscle phenotype and endurance capacity are typically induced by endurance but not heavy resistance exercise. Here, we tested the hypothesis that vibroX activates genes associated with mitochondrial biogenesis and angiogenesis. Eight healthy, recreationally resistance-trained young men performed either vibroX or resistance exercise (RES) in a randomised, cross-over design. Needle biopsies (M. vastus lateralis) were obtained at rest and 3 h post-exercise. Changes in relative gene expression levels were assessed by real-time quantitative PCR. After vibroX, vascular endothelial growth factor and peroxisome proliferator-activated receptor-γ coactivator 1α mRNA abundances increased to 2- and 4.4-fold, respectively, but did not significantly change above resting values after RES. Other genes involved in mitochondrial biogenesis were not affected by either exercise modality. While vibroX increased the expression of hexokinase II, xanthine dehydrogenase, and manganese superoxide dismutase mRNA, there were no changes in these transcripts after RES. This study demonstrates that high load resistance exercise with superimposed whole-body vibration and sustained vascular occlusion activates metabolic and angiogenic gene programs, which are usually activated after endurance but not resistance exercise. Thus, targeted modification of high load resistance exercise by vibration and vascular occlusion might represent a novel strategy to induce endurance-type muscle adaptations.

Haematocrit is invalid for estimating red cell volume: a prospective study in male volunteers.

BACKGROUND: Although haematocrit and haemoglobin value are concentrations, they are commonly used to guide clinical decisions involving red cell and plasma volumes. A study challenging this convention systematically co-determined and compared these measures. MATERIALS AND METHODS: Using a non-radioactive double-tracer technique to assess blood volume components, measurements were taken once in 46 healthy male endurance athletes. The best predictors of blood composition were derived from the first 36 athletes by automated stepwise forward selection of non-invasive metric parameters (age, weight, height, body surface area and body mass index) and the resulting formulae validated in the remaining ten volunteers. Haematocrit, haemoglobin concentration, red cell volume and plasma volume were measured again 4 weeks later in eight randomly selected volunteers. RESULTS: Red cell volume (2,282±283 mL) did not correlate with either haematocrit (0.42±0.02) or haemoglobin concentration (14.2±0.8, P>0.05, resp.), but was predictable from body surface area (red cell volume [mL]=1,547 × body surface area [m2]-723; r=.88, P<0.01). A similar accuracy was unobtainable using any potential predictor for plasma or blood volume, haematocrit or haemoglobin concentration. Red cell volume showed high intra-individual stability when measured again after 4 weeks, whereas plasma volume oscillated in both directions by up to 22%. DISCUSSION: Only red cell volume shows sufficiently stable intra- and interindividual values to be an accurate, objective indicator of normality in blood composition. The measurement technique is feasible in the outpatient setting and this parameter provides effective, robust, and readily available diagnostic information that might be useful in numerous clinical situations. Its clinical significance does, however, remain to be demonstrated.

Fatigue-induced increase in intracortical communication between mid/anterior insular and motor cortex during cycling exercise.

In the present study, intracortical communication between mid/anterior insular and motor cortex was investigated during a fatiguing cycling exercise. From 16 healthy male subjects performing a constant-load test at 60% peak oxygen consumption (VO(2peak)) until volitional exhaustion, electroencephalography data were analysed during repetitive, artefact-free periods of 1-min duration. To quantify fatigue-induced intracortical communication, mean intra-hemispheric lagged phase synchronization between mid/anterior insular and motor cortex was calculated: (i) at the beginning of cycling; (ii) at the end of cycling; and (iii) during recovery cycling. Results revealed significantly increased lagged phase synchronization at the end of cycling, which returned to baseline during recovery cycling after subjects' cessation of exercise. Following previous imaging studies reporting the mid/anterior insular cortex as an essential instance processing a variety of sensory stimuli and signalling forthcoming physiological threat, our results provide further evidence that during a fatiguing exercise this structure might not only integrate and evaluate sensory information from the periphery, but also act in communication with the motor cortex. To the best of our knowledge, this is the first study to empirically demonstrate that muscle fatigue leads to changes in interaction between structures of a brain's neural network.

Lactate minimum is valid to estimate maximal lactate steady state in moderately and highly trained subjects.

Some evidence exists that the determination of maximal lactate steady state (MLSS) with lactate minimum (LM) in highly trained athletes is not as accurate as in less trained athletes. Therefore, we compared power output at LM with power output MLSS in moderately up to highly trained subjects. 63 subjects performed a test on a cycle ergometer to determine power output at LM and 3 or more constant-load tests of 30 minutes to determine power output at MLSS. Mean power output at LM (245 ± 29 W; mean ± SD) was slightly lower than power output at MLSS (255 ± 32 W). The correlation between power output at MLSS and LM was high, and the regression line runs parallel to the line of identity showing that the results of highly trained subjects agree with the results of less trained subjects (LM and MLSS r = 0.867, p < 0.001). The modified blood-lactate kinetic in highly trained athletes compared with less trained persons does not impair accuracy at LM. Therefore, we suggest LM as a valid and meaningful concept to estimate power output at MLSS in 1 single test in moderately up to highly trained athletes.

Mitochondrial capacity is affected by glycemic status in young untrained women with type 1 diabetes but is not impaired relative to healthy untrained women.

In this study, we examined whether glycemic status influences aerobic function in women with type 1 diabetes and whether aerobic function is reduced relative to healthy women. To this end, we compared several factors determining aerobic function of 29 young sedentary asymptomatic women (CON) with 9 women of similar age and activity level with type 1 diabetes [DIA, HbA1c range = 6.9-8.2%]. Calf muscle mitochondrial capacity was estimated by (31)P-magnetic resonance spectroscopy. Capillarization and muscle fiber oxidative enzyme activity were assessed from vastus lateralis and soleus muscle biopsies. Oxygen uptake and cardiac output were evaluated by ergospirometry and N(2)O/SF(6) rebreathing. Calf muscle mitochondrial capacity was not different between CON and DIA, as indicated by the identical calculated maximal rates of oxidative ATP synthesis [0.0307 (0.0070) vs. 0.0309 (0.0058) s(-1), P = 0.930]. Notably, HbA1c was negatively correlated with mitochondrial capacity in DIA (R(2) = 0.475, P = 0.040). Although HbA1c was negatively correlated with cardiac output (R(2) = 0.742, P = 0.013) in DIA, there was no difference between CON and DIA in maximal oxygen consumption [2.17 (0.34) vs. 2.21 (0.32) l/min, P = 0.764], cardiac output [12.1 (1.9) vs. 12.3 (1.8) l/min, P = 0.783], and endurance capacity [532 (212) vs. 471 (119) s, P = 0.475]. There was also no difference between the two groups either in the oxidative enzyme activity or capillary-to-fiber ratio. We conclude that mitochondrial capacity depends on HbA1c in untrained women with type 1 diabetes but is not reduced relative to untrained healthy women.

Maximum ground reaction force in relation to tibial bone mass in children and adults.

PURPOSE: The purpose of the study was to assess maximum voluntary forefoot ground reaction force during multiple one-legged hopping (F m1LH) and to determine the correlation between tibial volumetric bone mineral content (vBMC, a valid surrogate of bone strength) and F m1LH. METHODS: One hundred eighty-five females (8-82 yr old) and 138 males (8-71 yr old) performed multiple one-legged hopping to measure F m1LH acting on the forefoot during landing. Peripheral quantitative computed tomography scans were obtained to assess vBMC at 4%, 14%, 38%, and 66% of tibia length and calf muscle cross-sectional area at the 66% site. RESULTS: In all 323 participants, F m1LH corresponded to 3-3.5 times body weight, and F m1LH predicted vBMC 14% by 84.0% (P < 0.001). vBMC 14% was better correlated with F m1LH than with the calf muscle cross-sectional area in both males (R2 = 0.841 vs R2 = 0.724) and females (R2 = 0.765 vs R2 = 0.597). F m1LH and vBMC14% both increased during growth and afterward remained constant or decreased with age but never increased above the values reached at the end of puberty. F m1LH decreased by 23.6% between 21-30 and 61-82 yr in females and by 14.0% between 31-40 and 51-71 yr in males. vBMC 14% decreased by 13.7% in females between 21-30 and 61-82 yr but remained unchanged in adult males. CONCLUSIONS: Multiple one-legged hopping yields the highest (i.e., maximum) ground reaction force relative to other jumping maneuvers. Because bone strength is strongly governed by maximum muscle force, the concurrent assessment of peripheral quantitative computed tomography-derived bone strength and F m1LH might represent a new approach for the operational evaluation of musculoskeletal health.

Spinal opioid receptor-sensitive muscle afferents contribute to the fatigue-induced increase in intracortical inhibition in healthy humans.

We investigated the influence of spinal opioid receptor-sensitive muscle afferents on cortical changes following fatiguing unilateral knee-extensor exercise. On separate days, seven subjects performed an identical five sets of intermittent isometric right-quadriceps contractions, each consisting of eight submaximal contractions [63 ± 7% maximal voluntary contraction (MVC)] and one MVC. The exercise was performed following either lumbar interspinous saline injection or lumbar intrathecal fentanyl injection blocking the central projection of spinal opioid receptor-sensitive lower limb muscle afferents. To quantify exercise-induced peripheral fatigue, quadriceps twitch force (Q(tw,pot)) was assessed via supramaximal magnetic femoral nerve stimulation before and after exercise. Motor evoked potentials and cortical silent periods (CSPs) were evaluated via transcranial magnetic stimulation of the motor cortex during a 3% MVC pre-activation period immediately following exercise. End-exercise quadriceps fatigue was significant and similar in both conditions (Q(tw,pot) -35 and -39% for placebo and fentanyl, respectively; P = 0.38). Immediately following exercise on both days, motor evoked potentials were similar to those obtained prior to exercise. Compared with pre-exercise baseline, CSP in the placebo trial was 21 ± 5% longer postexercise (P < 0.01). In contrast, CSP following the fentanyl trial was not significantly prolonged compared with the pre-exercise baseline (6 ± 4%). Our findings suggest that the central effects of spinal opioid receptor-sensitive muscle afferents might facilitate the fatigue-induced increase in CSP. Furthermore, since the CSP is thought to reflect inhibitory intracortical interneuron activity, which may contribute to central fatigue, our findings imply that spinal opioid receptor-sensitive muscle afferents might influence central fatigue by facilitating intracortical inhibition.

Limitation of physical performance in a muscle fatiguing handgrip exercise is mediated by thalamo-insular activity.

In this study, we investigated central/supraspinal processes mediating cessation of a muscle fatiguing exercise. Fifteen male subjects performed 39 intermittent, isometric handgrip contractions (13 s on, 5-6 s off) with the dominant right hand while brain activation was assessed by means of functional magnetic resonance imaging (fMRI). An adaptive, partly stochastic protocol was designed such that in approximately 50% of the contraction trials the required force could not be held until the end of the trial (task failure trial). Trials performed in compliance with the force requirements (succeeded trial) were compared with task failure trials concerning neural activity during a small time window before task failure occurred. The data revealed significantly increased activation contralaterally in both the mid/anterior insular cortex and the thalamus during the investigated time window in the case of subsequent task failure. In accordance with other studies investigating sensations that alert the organism to urgent homeostatic imbalance such as air hunger, hunger for food, and pain, we assume that an increased thalamo-insular activation in the context of a fatigue-induced handgrip exercise could reflect increased homeostatic disturbance in the exercising muscle and may be of essential importance by mediating task failure to maintain the integrity of the organism.

Cardiac output but not stroke volume is similar in a Wingate and VO2peak test in young men.

Wingate test (WT) training programmes lasting 2-3 weeks lead to improved peak oxygen consumption. If a single 30 s WT was capable of significantly increasing stroke volume and cardiac output, the increase in peak oxygen consumption could possibly be explained by improved oxygen delivery. Thus, we investigated whether a single WT increases stroke volume and cardiac output to similar levels than those obtained at peak exercise during a graded cycling exercise test (GXT) to exhaustion. Fifteen healthy young men (peak oxygen consumption 45.0 ± 5.3 ml kg(-1) min(-1)) performed one WT and one GXT on separate days in randomised order. During the tests, we estimated cardiac output using inert gas rebreathing (nitrous oxide and sulphur hexafluoride) and subsequently calculated stroke volume. We found that cardiac output was similar (18.2 ± 3.3 vs. 17.9 ± 2.6 l min(-1); P = 0.744), stroke volume was higher (127 ± 37 vs. 94 ± 15 ml; P < 0.001), and heart rate was lower (149 ± 26 vs. 190 ± 12 beats min(-1); P < 0.001) at the end (27 ± 2 s) of a WT as compared to peak exercise during a GXT. Our results suggest that a single WT produces a haemodynamic response which is characterised by similar cardiac output, higher stroke volume and lower heart rate as compared to peak exercise during a GXT.

Electric pulse stimulation of cultured murine muscle cells reproduces gene expression changes of trained mouse muscle.

Adequate levels of physical activity are at the center of a healthy lifestyle. However, the molecular mechanisms that mediate the beneficial effects of exercise remain enigmatic. This gap in knowledge is caused by the lack of an amenable experimental model system. Therefore, we optimized electric pulse stimulation of muscle cells to closely recapitulate the plastic changes in gene expression observed in a trained skeletal muscle. The exact experimental conditions were established using the peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) as a marker for an endurance-trained muscle fiber. We subsequently compared the changes in the relative expression of metabolic and myofibrillar genes in the muscle cell system with those observed in mouse muscle in vivo following either an acute or repeated bouts of treadmill exercise. Importantly, in electrically stimulated C2C12 mouse muscle cells, the qualitative transcriptional adaptations were almost identical to those in trained muscle, but differ from the acute effects of exercise on muscle gene expression. In addition, significant alterations in the expression of myofibrillar proteins indicate that this stimulation could be used to modulate the fiber-type of muscle cells in culture. Our data thus describe an experimental cell culture model for the study of at least some of the transcriptional aspects of skeletal muscle adaptation to physical activity. This system will be useful for the study of the molecular mechanisms that regulate exercise adaptation in muscle.