Leg Power Output Research Articles

Performance analysis and mechanical determinants of the opening lap of the team sprint in elite-leveltrack cycling.

The team sprint (TS) is a three-lap pursuit and the most revered event in track sprint cycling. The opening lap of the TS is an important determinant to the overall performance. But despite it being the most controlled and repeatable task in track sprint cycling, very little data are available to better understand the performance of the opening lap. The aim of this study was split into three-parts: part one, to better understand the profile and the indices thought to be determinants of the opening lap of the TS in elite sprint track cyclists. Part two of the study examined all available timing splits (15, 65, 125 and 250m) from 36 standing-start laps. Part three of the study examined the peak torque outputs and peak power outputs of different various starts performed over a 3-month period. The results showed time to 125m exhibited a near perfect relationship with starter lap performance. Very strong relationships were seen with 15 and 65m split times and final lap performance. Peak torque of the lead starting leg and peak power output were shown to be highly predictive 15m, 65 and 125m performance in training. These data suggested the first 15m is highly important and predicts a disproportionately high level of final opening lap time performance. Therefore, it is likely that peak power output normalised to system mass and peak torque of lead leg is a strong determinant of overall performance in the TS.

Prediction of rowing ergometer performance by technical and core stability parameters

ABSTRACT The purpose of this study was to evaluate the influence of technical and core stability parameters on rowing ergometer performance defined as mean power at the handle. Twenty-four high-level rowers were evaluated at their competitive stroke rate on an instrumented RowPerfect 3 ergometer to determine leg, trunk and arm power output, while trunk and pelvis 3D kinematics were measured. Linear mixed models revealed that mean power at the handle was predicted by the power output of legs, trunk and arms (r2 = 0.99), with trunk power being the best predictor. Time to peak power, work ratio and mean to peak power ratio were relevant technical parameters significantly predicting the different segments’ power. In addition, a greater trunk range of motion significantly influenced the power produced by this segment. Accordingly, achieving an earlier peak power together with enhanced work production at the trunk and arm levels, as well as distributing the segments power over the whole drive phase, could serve as recommendations for technical training of rowers on dynamic ergometers in order to produce higher power output. Furthermore, the trunk appears to play a major role as a power producer within the kinetic chain from the legs to the arms.

The relationship between physical characteristics and match collision performance among elite international female rugby union players

ABSTRACT This study investigated whether anthropometric and physical abilities explained variance in match collision performance among international female rugby union players. Physical performance and anthropometric data for fifty-one international female rugby union players, and collision actions categorised as “effort” or “performance” variables, from 20 international matches, were analysed using partial least squares regression. Among forwards, variance in carries/min was explained (R2 = .22) by a combination of; body mass, skinfolds, acceleration momentum and negative associations with mean aerobic speed and single-leg isometric squat relative force (SLISO/kgBM). Variance in collision dominance among forwards was explained (R2 = .21) by lower skinfolds and higher acceleration momentum, while tackles/min (R2 = .19) were explained by greater jumping power and single-leg isometric squat (SLISO). Among backs, variance in tackles/min (R2 = .54) was explained by greater bench press, SLISO and SLISO/kgBM. Variance in collision dominance among backs was explained (R2 = .23) by negative and positive associations with body mass and SLISO/kgBM, respectively. These findings suggest the development of physical characteristics, such as body mass and composition, strength and power contribute towards successful collision actions among international female rugby union players. The contribution of different physical characteristics towards collision events is dependent on position, and whether the collision event is categorised by “performance” or “effort”. It is suggested that physical training programmes should reflect this level of specificity. Highlights Among elite female rugby union forwards, acceleration momentum, body mass and skinfolds are positively associated with winning collisions and carrying the ball into contact more frequently, whilst tackle frequency is positively associated with relative leg strength and power output. Among elite female backs, the ability to win collisions is positively associated with relative leg power output, and negatively associated with body mass. Tackle frequency is associated with maximum upper- and lower-body strength in this group. Physical characteristics account for some of the variability in collision performance, but interpretation of these findings should consider that factors such as technique during collision events may account for a larger proportion of total variance. Sports science practitioners can improve collision performance, to varying degrees, by enhancing specific gross physical characteristics, according to a player’s position and the tactical role they are expected to fulfil.

The motor and the brake of the trailing leg in human walking: transtibial amputation limits ankle-knee torque covariation.

Lower-limb amputation limits inherent motor abundance in the locomotor system and impairs walking mechanics. Able-bodied walkers vary ankle torque to adjust step-to-step leg force production as measured by resultant ground reaction forces. Simultaneously, knee torque covaries with ankle torque to act as a brake, resulting in consistent peak leg power output measured by external mechanical power generated on the center of mass. Our objective was to test how leg force control during gait is affected by joint torque variance structure in the amputated limb. Within the framework of the uncontrolled manifold analysis, we measured the Index of Motor Abundance (IMA) to quantify joint torque variance structure of amputated legs and its effect on leg force, where IMA > 0 indicates a stabilizing structure. We further evaluated the extent to which IMA in amputated legs used individual (INV) and coordinated (COV) joint control strategies. Amputated legs produced IMA and INV values similar to intact legs, indicating that torque deviations of the prosthetic ankle can modulate leg force at the end of stance phase. However, we observed much lower COV values in the amputated leg relative to intact legs indicating that biological knee joint torque of the amputated leg does not covary with prosthetic ankle torque. This observation suggests inter-joint coordination during gait is significantly limited as a result of transtibial amputation and may help explain the higher rate of falls and impaired balance recovery in this population, pointing to a greater need to focus on inter-joint coordination within the amputated limb.

Jumping mechanism in the marsh beetles (Coleoptera: Scirtidae)

The jumping mechanism with supporting morphology and kinematics is described in the marsh beetle Scirtes hemisphaericus (Coleoptera: Scirtidae). In marsh beetles, the jump is performed by the hind legs by the rapid extension of the hind tibia. The kinematic parameters of the jump are: 139–1536 m s−2 (acceleration), 0.4–1.9 m s−1 (velocity), 2.7–8.4 ms (time to take-off), 0.2–5.4 × 10–6 J (kinetic energy) and 14–156 (g-force). The power output of a jumping leg during the jumping movement is 3.5 × 103 to 9.6 × 103 W kg−1. A resilin-bearing elastic extensor ligament is considered to be the structure that accumulates the elastic strain energy. The functional model of the jumping involving an active latching mechanism is proposed. The latching mechanism is represented by the conical projection of the tibial flexor sclerite inserted into the corresponding socket of the tibial base. Unlocking is triggered by the contraction of flexor muscle pulling the tibial flexor sclerite backwards which in turn comes out of the socket. According to the kinematic parameters, the time of full extension of the hind tibia, and the value of the jumping leg power output, this jumping mechanism is supposed to be latch-mediated spring actuation using the contribution of elastically stored strain energy.

Contribution of Strength, Speed and Power Characteristics to Change of Direction Performance in Male Basketball Players

This study aimed to investigate the relationships between the modified t−agility test (MAT) time and muscular strength and power of lower limb extensors, adductors (AD), and abductors (AB). Nineteen male basketball players performed: linear sprint tests at 5 m and 20 m, MAT, countermovement (CMJ) and drop jump (DJ), leg press exercise, AD and AB hip maximum isometric strength measurements. All of them were left leg dominant. The correlation analysis showed a significant, moderate to very large negative relationship between MAT test time initiated to the left and height of CMJ and DJ (r = −0.69 and −0.54; p < 0.01, both), left (r = −0.56; p < 0.01) and right leg (r = −0.41; p < 0.05) AD, left leg AB (r = −0.48; p < 0.05) maximum isometric strength, left (r = −0.72; p < 0.01) and right (r = −0.64; p < 0.01) leg power output in leg press. In the case of the MAT test initiated on the right side first, the correlations were found between CMJ height (r = −0.46; p < 0.05), AD and AB maximum isometric strength of left (r = −0.58 and −0.84; p < 0.01, both) and right leg (r = −0.58 and −0.79; p < 0.01, both), and both legs power output in leg press (r = −0.66 for left and r = −0.59 for right; p < 0.01, both). The regression analyses showed that the prediction model of left leg press peak power, left leg AD maximum isometric strength, and CMJ height could explain up to 93% of the MAT test time initiated to the left first. The model, including left leg AB and AD maximum isometric strength, could explain up to 83% of the MAT test time initiated to the right side first. Findings from this study demonstrate that AB and AD maximum isometric muscle strength are highly related to MAT test performance, which is particularly important when the first turn is performed in the non−dominant direction in this test.

Effects of Power-Oriented Resistance Training During an Altitude Camp on Strength and Technical Performance of Elite Judokas.

This study investigated the effect of a 3-week power-oriented resistance training program performed at moderate altitude on leg power output variables in a countermovement jump, a related judo technique (ippon-seoi-nage) and the relationship between them. Twenty-four elite male judokas were randomly assigned to a hypobaric hypoxia or normoxia group. Mechanical outputs from an incremental loaded countermovement jump test and the kinematic variables transferred to a dummy during an ippon-seoi-nage test (time to execution and movement accelerations) were assessed before, after, 1 and 2 weeks after training. Results indicated an increase in explosive leg capacity both at moderate altitude (2320 m.a.s.l.) and sea level. The hypoxia group showed additional benefits when compared to normoxia group for peak velocities with different percentages of the body weight, maximal theoretical velocity and jump height after the training period, and these additional benefits in jump height were maintained 2 weeks after training. The hypoxia group achieved a higher peak performance in peak velocity and jump height than normoxia group (peak velocity: 8.8 vs. 5.6%, jump height: 8.2 vs. 1.4%, respectively) and was achieved earlier in hypoxia (after training) than in normoxia (1 week after training). However, there was a detrimental effect for the hypoxia group on the times of execution and acceleration of the ippon-seoi-nage compared to the normoxia group. These results suggest that altitude training may induce faster and greater improvements in explosive leg extension capacity. Specific technique-oriented training should be included at altitude to prevent technique impairment.

Anaerobic Power Assessment in Athletes: Are Cycling and Vertical Jump Tests Interchangeable?

Regularly assessing anaerobic power is important for athletes from sports with an explosive strength component. Understanding the differences and overlap between different assessment methods might help coaches or smaller-scale testing facilities maximize financial and temporal resources. Therefore, this study investigated the degree to which cycling sprint and vertical jump tests are interchangeable for determining peak mechanical leg power output in strength-trained athletes. Professional skiers (n = 19) performed unloaded squat jumps (SJ) and other jump forms on a force plate and a six-second cycling sprint (6sCS) test on an ergometer on six occasions over two years. Along with cross-sectional correlations between cycling and jumping power, correlations between longitudinal percent changes and agreement between magnitude-based inferences about individual changes were assessed. Among the tested jump forms, SJ reflected 6sCS best. However, despite extremely large cross-sectional correlation coefficients (0.92) between 6sCS and SJ, and moderate (Pearson’s r = 0.32 for 6sCS with SJ over one-year time spans) to large (r = 0.68 over shorter time spans) correlation coefficients on percent changes, magnitude-based inferences agreed in only around 50% of cases. Thus, for making qualitative assessments about the development of anaerobic power over time in athletes, cycling sprint and squat jump tests are not interchangeable. Rather, we recommend employing the test form that best reflects athletes’ strength and conditioning training.

Body Composition, Neuromuscular Performance, and Mobility: Comparison Between Regularly Exercising and Inactive Older Women.

The purpose of this study was to evaluate the differences in body composition, neuromuscular performance, and mobility in healthy, regularly exercising and inactive older women, and examine the relationship between skeletal muscle indices and mobility. Overall, 32 healthy older women participated. They were divided into groups according to their physical activity history as regularly exercising (n = 22) and inactive (n = 10) women. Body composition, hand grip strength, leg extensor muscle strength, rapid force development, power output, and mobility indices were assessed. Regularly exercising women had lower fat mass and higher values for leg extensor muscle strength and muscle quality, and also for mobility. Leg extensor muscle strength and power output during vertical jumping and appendicular lean mass per unit of body mass were associated with mobility in healthy older women. It was concluded that long-term regular exercising may have beneficial effects on body composition and physical function in older women.

Muscle coordination limits efficiency and power output of human limb movement under a wide range of mechanical demands.

This study investigated the influence of cycle frequency and workload on muscle coordination and the ensuing relationship with mechanical efficiency and power output of human limb movement. Eleven trained cyclists completed an array of cycle frequency (cadence)-power output conditions while excitation from 10 leg muscles and power output were recorded. Mechanical efficiency was maximized at increasing cadences for increasing power outputs and corresponded to muscle coordination and muscle fiber type recruitment that minimized both the total muscle excitation across all muscles and the ineffective pedal forces. Also, maximum efficiency was characterized by muscle coordination at the top and bottom of the pedal cycle and progressive excitation through the uniarticulate knee, hip, and ankle muscles. Inefficiencies were characterized by excessive excitation of biarticulate muscles and larger duty cycles. Power output and efficiency were limited by the duration of muscle excitation beyond a critical cadence (120-140 rpm), with larger duty cycles and disproportionate increases in muscle excitation suggesting deteriorating muscle coordination and limitations of the activation-deactivation capabilities. Most muscles displayed systematic phase shifts of the muscle excitation relative to the pedal cycle that were dependent on cadence and, to a lesser extent, power output. Phase shifts were different for each muscle, thereby altering their mechanical contribution to the pedaling action. This study shows that muscle coordination is a key determinant of mechanical efficiency and power output of limb movement across a wide range of mechanical demands and that the excitation and coordination of the muscles is limited at very high cycle frequencies.

Influence of Affective Stimuli on Leg Power Output and Associated Neuromuscular Parameters during Repeated High Intensity Cycling Exercises.

The aim of this study was to examine the impact of emotional eliciting pictures on neuromuscular performance during repetitive supramaximal cycling exercises (RSE). In a randomized order, twelve male participants were asked to perform five 6-s cycle sprints (interspaced by 24 s of recovery) on a cycle ergometer in front of neutral, pleasant or unpleasant pictures. During each RSE, mean power output (MPO) and electromyographic activity [root mean square (RMS) and median frequency (MF)] of the vastus lateralis and vastus medialis muscles were analyzed. Neuromuscular efficiency (NME) was calculated as the ratio of MPO to RMS. Higher RMS (232.17 ± 1.17 vs. 201.90 ± 0.47 μV) and MF (68.56 ± 1.78 vs. 64.18 ± 2.17 Hz) were obtained in pleasant compared to unpleasant conditions (p < 0.05). This emotional effect persisted from the first to the last sprint. Higher MPO was obtained in pleasant than in unpleasant conditions (690.65 ± 38.23 vs. 656.73 ± 35.95 W, p < 0.05). However, this emotional effect on MPO was observed only for the two first sprints. NME decreased from the third sprint (p < 0.05), which indicated the occurrence of peripheral fatigue after the two first sprints. These results suggested that, compared with unpleasant pictures, pleasant ones increased the neuromuscular performance during RSE. Moreover, the disappearance of the beneficial effect of pleasant emotion on mechanical output from the third sprint appears to be due to peripheral fatigue.

Relationship between vertical jump and maximal power output of legs and arms: effects of ethnicity and sport.

The hypothesis that ethnicity and sport practice influence the relationship between maximal power in cycling (P(max)) and countermovement jump (CMJ) has been studied by relating CMJ and P(max) in two groups (volleyball players, VB, and physical education students, PES) including subjects with Caucasian (67 C) or West African (39 WA) origins. Maximal power of the arms (P(max) Arms) was also measured. A two-way analysis of variance (groups × ethnicity) showed significant effects of both factors upon CMJ, which was higher in WA and VB, P = 0.002 and P < 0.001, respectively. Within WA, CMJ was significantly higher in VB (0.732 ± 0.057 m) than in PES (0.661 ± 0.082 m), although there was no difference in P(max) (14.7 ± 1.7 vs 14.7 ± 1.9 W/kg). CMJ was significantly higher in WA (0.69 ± 0.08 vs 0.65 ± 0.09 m in C, P = 0.002) without significant interethnic difference in P(max) (14.7 ± 1.8 in WA, and 14.8 ± 1.9 W/kg in C). The CMJ-P(max) relationships were different in C and WA (P = 0.003). Therefore, CMJ predicted from P(max) would be underestimated in WA. The same difference was observed for the relationship between CMJ and P(max) Arms. These results were confirmed by the comparison with previous P(max) -CMJ relationship in the literature, collected in Caucasian and African subjects with the same protocols.

Aerobic exercise improves gastrointestinal motility in psychiatric inpatients.

To evaluate the benefit of aerobic exercise on colonic transit time (CTT) for psychiatric inpatients in a closed ward. Sixty consecutive adult inpatients of the Somang Hospital Psychiatry Unit (Eumsung-gun, South Korea), without CTT-related diseases or drug therapies, were recruited for study from March to June of 2012. Upon enrollment, the patients were randomly assigned to partake in a 12-wk instructor-led group aerobic exercise program (exercise group; n = 30) or to maintain their ordinary daily activities (control group; n = 30). The exercise program was structured as 10 min warm-up (stretching), 40 min exercise, and 10 min cool-down (stretching) for three days each week. The exercise sessions consisted of walking only in week one and aerobics from weeks two to 12, with increasing intensity (50% heart rate reserve (HRR) for weeks one to four, 60% HRR for weeks five to eight, and 70% HRR for weeks nine to 12). CTT was measured before (baseline) and after (week 12) the exercise program, in duplicate (on days four and seven), using abdominal radiography and the multiple radio-opaque marker technique. Changes in the exercising patients' CTT and weight-, cardiovascular- and fitness-related parameters were statistically assessed. The study dropout rate was 30.0%, with 23 patients in the exercise group and 19 patients in the control group completing the study. At week 12, the exercise group showed decreases in body weight (mean ± SE) baseline: 69.4 ± 2.8 vs study-end: 67.6 ± 2.7; P < 0.635) and body mass index (BMI) (25.2 ± 1.1 vs 24.9 ± 0.8; P < 0.810), but the extent of change was not significantly different from that experienced by the control group (body weight: 68.8 ± 4.0 vs 68.8 ± 3.9; BMI: 24.3 ± 1.1 vs 24.4 ± 1.2). However, the exercise group showed significant improvements in leg muscle strength (baseline: 41.7 ± 4.3 vs study-end: 64.1 ± 5.0; P < 0.001), cardio-respiratory endurance (120.5 ± 4.5 vs 105.4 ± 2.8; P < 0.004), and leg muscle elasticity and power output (21.5 ± 2.6 vs 30.6 ± 2.8; P < 0.001). The exercise group showed an exercise-induced reduction in total CTT (baseline: 54.2 ± 8.0 vs 30.3 ± 6.1), which was significantly different from that experienced by the control group over the 12-wk period (48.6 ± 9.3 vs 48.3 ± 12.3; P = 0.027); however, the exercise-induced decreases in CTT involving the three colonic segments examined (right, left and recto-sigmoid) showed no significant differences from the control group. A 12-wk aerobic exercise program can benefit psychiatric inpatients by increasing intestinal motility, possibly decreasing risk of metabolic- and cardiovascular-related disease.

Elevated energy coupling and aerobic capacity improves exercise performance in endurance‐trained elderly subjects

Increased maximal oxygen uptake (V(O(2)max)), mitochondrial capacity and energy coupling efficiency are reported after endurance training (ET) in adult subjects. Here we test whether leg exercise performance (power output of the legs, P(max), at V(O(2)max)) reflects these improvements with ET in the elderly. Fifteen male and female subjects were endurance trained for a 6 month programme, with 13 subjects (69.5 ± 1.2 years old, range 65-80 years old; n = 7 males; n = 6 females) completing the study. This training significantly improved P(max) (Δ17%; P = 0.003), V(O(2)max) (Δ5.4%; P = 0.021) and the increment in oxygen uptake (V(O(2))) above resting (ΔV(O(2)m-r) = V(O(2)max) - V(O(2)rest; Δ9%; P < 0.02). In addition, evidence of improved energy coupling came from elevated leg power output per unit V(O(2))at the aerobic capacity [Δ(P(max)/ΔV(O(2)m-r)); P = 0.02] and during submaximal exercise in the ramp test as measured by delta efficiency (ΔP(ex)/ΔV(O(2)); P = 0.04). No change was found in blood lactate, muscle glycolysis or fibre type. The rise in P(max) paralleled the improvement in muscle oxidative phosphorylation capacity (ATP(max)) in these subjects. In addition, the greater exercise energy coupling [Δ(P(max)/ΔV(O(2)m-r)) and delta efficiency] was accompanied by increased mitochondrial energy coupling as measured by elevated ATP production per unit mitochondrial content in these subjects. These results suggest that leg exercise performance benefits from elevations in energy coupling and oxidative phosphorylation capacity at both the whole-body and muscle levels that accompany endurance training in the elderly.

Exercise efficiency is reduced by mitochondrial uncoupling in the elderly

A reduction in exercise efficiency accompanies ageing in humans. Here we evaluated the impact of changes in the contractile-coupling and mitochondrial-coupling efficiencies on the reduction in exercise efficiency in the elderly. Nine adult (mean, 38.8 years old) and 40 elderly subjects (mean, 68.8 years old) performed a cycle ergometer test to measure O2 uptake and leg power output up to the aerobic limit ( ). Reduced leg power output per unit O2 uptake was reflected in a drop in delta efficiency (εD) from 0.27 ± 0.01 (mean ± SEM) in adults to 0.22 ± 0.01 in the elderly group. Similar declines with age were apparent for both the leg power output at and the ATP generation capacity (ATPmax) determined in vivo using (31)P magnetic resonance spectroscopy. These similar declines resulted in unchanged contractile-coupling efficiency values (εC) in the adult (0.50 ± 0.05) versus the elderly group (0.58 ± 0.04) and agreed with independent measures of muscle contractile-coupling efficiency in human quadriceps (0.5). The mitochondrial-coupling efficiency calculated from the ratio of delta to contractile-coupling efficiencies in the adults (εD/εC = 0.58 ± 0.08) corresponded to values for well-coupled mitochondria (0.6); however, εD/εC was significantly lower in the elderly subjects (0.44 ± 0.03). Conversion of ATPmax per mitochondrial volume (ATPmax/Vv[mt,f]) reported in these groups into thermodynamic units confirmed this drop in mitochondrial-coupling efficiency from 0.57 ± 0.08 in adults to 0.41 ± 0.03 in elderly subjects. Thus, two independent methods revealed that reduced mitochondrial-coupling efficiency was a key part of the drop in exercise efficiency in these elderly subjects and may be an important part of the loss of exercise performance with age.

Muscle Damage and Its Relationship with Muscle Fatigue During a Half-Iron Triathlon

BackgroundTo investigate the cause/s of muscle fatigue experienced during a half-iron distance triathlon.Methodology/Principal FindingsWe recruited 25 trained triathletes (36±7 yr; 75.1±9.8 kg) for the study. Before and just after the race, jump height and leg muscle power output were measured during a countermovement jump on a force platform to determine leg muscle fatigue. Body weight, handgrip maximal force and blood and urine samples were also obtained before and after the race. Blood myoglobin and creatine kinase concentrations were determined as markers of muscle damage.ResultsJump height (from 30.3±5.0 to 23.4±6.4 cm; P<0.05) and leg power output (from 25.6±2.9 to 20.7±4.6 W · kg−1; P<0.05) were significantly reduced after the race. However, handgrip maximal force was unaffected by the race (430±59 to 430±62 N). Mean dehydration after the race was 2.3±1.2% with high inter-individual variability in the responses. Blood myoglobin and creatine kinase concentration increased to 516±248 µg · L−1 and 442±204 U · L−1, respectively (P<0.05) after the race. Pre- to post-race jump change did not correlate with dehydration (r = 0.16; P>0.05) but significantly correlated with myoglobin concentration (r = 0.65; P<0.001) and creatine kinase concentration (r = 0.54; P<0.001).Conclusions/significanceDuring a half-iron distance triathlon, the capacity of leg muscles to produce force was notably diminished while arm muscle force output remained unaffected. Leg muscle fatigue was correlated with blood markers of muscle damage suggesting that muscle breakdown is one of the most relevant sources of muscle fatigue during a triathlon.

Commentaries on Viewpoint: Can muscle size fully account for strength differences between children and adults?

# {#article-title-2} to the editor: As comprehensively explained in their Viewpoint article ([1][1]), the answer to the question posed in the title has received conflicting answers. Since the contractile machinery in children is the same as that in adults, there is no reason to believe that

Respiratory and leg muscles perceived exertion during exercise at altitude

We compared the rate of perceived exertion for respiratory (RPE,resp) and leg (RPE,legs) muscles, using a 10-point Borg scale, to their specific power outputs in 10 healthy male subjects during incremental cycle exercise at sea level (SL) and high altitude (HA, 4559 m). Respiratory power output was calculated from breath-by-breath esophageal pressure and chest wall volume changes. At HA ventilation was increased at any leg power output by ∼ 54%. However, for any given ventilation, breathing pattern was unchanged in terms of tidal volume, respiratory rate and operational volumes of the different chest wall compartments. RPE,resp scaled uniquely with total respiratory power output, irrespectively of SL or HA, while RPE,legs for any leg power output was exacerbated at HA. With increasing respective power outputs, the rate of change of RPE,resp exponentially decreased, while that of RPE,legs increased. We conclude that RPE,resp uniquely relates to respiratory power output, while RPE,legs varies depending on muscle metabolic conditions.

Mitochondrial Dysfunction Impacts Exercise Efficiency In The Elderly

Reduced efficiency of mitochondrial generation of ATP from O2 is expected to lower leg power output per O2 uptake (i.e., exercise efficiency). PURPOSE: Here we test the impact of mitochondrial inefficiency in human quadriceps muscle (i.e., loss of phosphorylation capacity per mitochondrial content (ATPmax/Vv[mt,f] with age; J Physiol. 526.1: 203, 2000) on exercise efficiency of the elderly. METHODS: Mitochondrial coupling efficiency (ATP/O2) was determined from ATPmax/Vv[mt,f] using the maximum O2 uptake per mitochondrial content. Oxygen uptake and leg power output were elicited by cycle ergometer exercise. RESULTS: Lower mitochondrial coupling was found in elderly (4.3+0.3 SE, n=31; mean age = 69 yrs) vs. adult muscle (mean, 6.0+0.6, n=5; mean age = 39 yrs). Cycle ergometer exercise revealed a reduced exercise efficiency (delta efficiency: change in power output/change in O2 uptake) of cycling in elderly (22+1%; n=40) vs. adult (27+1%; n=9) groups. Contractile-coupling efficiency calculated from mitochondrial and exercise efficiency agreed with literature values (∼50-70%; J Physiol 586.7: 1993, 2008) but no difference was found between the elderly (54+3%) and adult (49+5%) groups. CONCLUSIONS: A reduced coupling of ATP supply from O2 uptake appears to be the basis of the lower delta efficiency in the elderly. These results indicate that mitochondrial dysfunction impacts exercise efficiency and may be a key part of the loss of exercise performance with age.

Contribution of respiratory muscle blood flow to exercise‐induced diaphragmatic fatigue in trained cyclists

We investigated whether the greater degree of exercise-induced diaphragmatic fatigue previously reported in highly trained athletes in hypoxia (compared with normoxia) could have a contribution from limited respiratory muscle blood flow. Seven trained cyclists completed three constant load 5 min exercise tests at inspired O(2) fractions (FIO2) of 0.13, 0.21 and 1.00 in balanced order. Work rates were selected to produce the same tidal volume, breathing frequency and respiratory muscle load at each FIO2 (63 +/- 1, 78 +/- 1 and 87 +/- 1% of normoxic maximal work rate, respectively). Intercostals and quadriceps muscle blood flow (IMBF and QMBF, respectively) were measured by near-infrared spectroscopy over the left 7th intercostal space and the left vastus lateralis muscle, respectively, using indocyanine green dye. The mean pressure time product of the diaphragm and the work of breathing did not differ across the three exercise tests. After hypoxic exercise, twitch transdiaphragmatic pressure fell by 33.3 +/- 4.8%, significantly (P < 0.05) more than after both normoxic (25.6 +/- 3.5% reduction) and hyperoxic (26.6 +/- 3.3% reduction) exercise, confirming greater fatigue in hypoxia. Despite lower leg power output in hypoxia, neither cardiac output nor QMBF (27.6 +/- 1.2 l min(-1) and 100.4 +/- 8.7 ml (100 ml)(-1) min(-1), respectively) were significantly different compared with normoxia (28.4 +/- 1.9 l min(-1) and 94.4 +/- 5.2 ml (100 ml)(-1) min(-1), respectively) and hyperoxia (27.8 +/- 1.6 l min(-1) and 95.1 +/- 7.8 ml (100 ml)(-1) min(-1), respectively). Neither IMBF was different across hypoxia, normoxia and hyperoxia (53.6 +/- 8.5, 49.9 +/- 5.9 and 52.9 +/- 5.9 ml (100 ml)(-1) min(-1), respectively). We conclude that when respiratory muscle energy requirement is not different between normoxia and hypoxia, diaphragmatic fatigue is greater in hypoxia as intercostal muscle blood flow is not increased (compared with normoxia) to compensate for the reduction in PaO2, thus further compromising O(2) supply to the respiratory muscles.