The effect of age on the power/duration relationship and the intensity-domain limits in sedentary men

The time to fatigue (t) in response to high-intensity constant-load exercise decreases hyperbolically with increasing power (W˙), at least in active and younger individuals [i.e. (W˙−θ_F)t=W′, where θ_F is the critical power asymptote and W′ is the curvature constant]. Little is known, however, about the combined effects of age and sedetarity on these parameters. We therefore evaluated 17 non-trained males (9 aged 60–75 years and 8 aged below 30 years) who underwent ramp-incremental cycle ergometry and, on different days, 4 high-intensity constant-load tests to t. Compared to their younger counterparts, the older subjects presented significantly lower maximum oxygen uptake (i.e. the maximum value of oxygen uptake attained at the end of a progressive exercise with the subject exerting a presumably maximal effort, μV˙O₂), estimated lactate threshold (V˙O₂θ_L), V˙O₂θ_F, and W′ (P < 0.05). Interestingly, however, both V˙O₂θ_L and V˙O₂θ_F, when expressed as a percentage of μV˙O₂, were higher in older than in younger men [61.8 (6.2)% versus 45.4 (4.6)% and 87.8 (7.3)% versus 79.0 (8.2)%, P < 0.05, respectively]. Therefore, age was associated with an increase in the relative magnitude of the “moderate”, sub-θ_L exercise-intensity domain (+30.4%), mainly at the expense of the “very-heavy”, supra-θ_F domain (−56%). Our results demonstrate that age and sedentarity are associated with: (1) marked reductions in both the aerobic (θ_F) and anaerobic (W′) determinants of the W˙/t relationship, and (2) changes in either the absolute or relative magnitudes of the exercise-intensity domains. These findings are consistent with the notion that endurance-related parameters are less diminished with ageing than the maximal capacity, thereby mitigating the deleterious effects of senescence in the functional capacity. Accepted: 5 April 2000     

Validity of the two-parameter model in estimating the anaerobic work capacity

The curvature of the power–time (P–t) relationship (W′) has been suggested to be constant when exercising above critical power (CP) and to represent the anaerobic work capacity (AWC). The aim of this study was to compare W′ to (1) the total amount of work performed above CP (W _90s′) and (2) the AWC, both determined from a 90s all-out fixed cadence test. Fourteen participants (age 30.5±6.5 years; body mass 67.8±10.3 kg), following an incremental VO_2max ramp protocol, performed three constant load exhaustion tests set at 103±3, 97±3 and 90±2% P-VO_2max to calculate W′ from the P–t relationship. Two 90s all-out efforts were also undertaken to determine W _90s′ (power output—time integral above CP) and AWC (power output—time integral above the power output expected from the measured VO₂). W′ (13.6±1.3 kJ) and W _90s′ (13.9±1.1 kJ; P=0.96) were not significantly different but were lower than AWC (15.9±1.2 kJ) by 24% (P=0.03) and 17%, respectively (P=0.04). All these variables were correlated (P<0.001) but great extents of disagreement were reported (0.2±6.4 kJ between W′ and W _90s′, 2.3±7.2 kJ between W′ and AWC, and 2.1±4.3 kJ between W _90s′ and AWC). The underestimation of AWC from both W′ and W _90s′ can be explained by the aerobic inertia not taking into consideration when determining the two latter variables. The low extents of agreement between W′, W _90s′ and AWC mean the terms should not be used interchangeably.     

Effect of heavy strength training on thigh muscle cross-sectional area, performance determinants, and performance in well-trained cyclists

The purpose of this study was to investigate the effect of heavy strength training on thigh muscle cross-sectional area (CSA), determinants of cycling performance, and cycling performance in well-trained cyclists. Twenty well-trained cyclists were assigned to either usual endurance training combined with heavy strength training [E + S; n = 11 (♂ = 11)] or to usual endurance training only [E; n = 9 (♂ = 7, ♀ = 2)]. The strength training performed by E + S consisted of four lower body exercises [3 × 4–10 repetition maximum (RM)], which were performed twice a week for 12 weeks. Thigh muscle CSA, maximal force in isometric half squat, power output in 30 s Wingate test, maximal oxygen consumption (VO_2max), power output at 2 mmol l⁻¹ blood lactate concentration ([la⁻]), and performance, as mean power production, in a 40-min all-out trial were measured before and after the intervention. E + S increased thigh muscle CSA, maximal isometric force, and peak power in the Wingate test more than E. Power output at 2 mmol l⁻¹ [la⁻] and mean power output in the 40-min all-out trial were improved in E + S (P < 0.05). For E, only performance in the 40-min all-out trial tended to improve (P = 0.057). The two groups showed similar increases in VO_2max (P < 0.05). In conclusion, adding strength training to usual endurance training improved determinants of cycling performance as well as performance in well-trained cyclists. Of particular note is that the added strength training increased thigh muscle CSA without causing an increase in body mass.     

Comparison of muscle cross-sectional area and strength between untrained women and men

The cross-sectional areas (CSA) of fat, muscle and bone tissues of the limb as well as maximal voluntary isokinetic strength were measured in untrained men (n=27) and women (n=26) aged 18–25 years. Anatomical CSA of the three tissues were determined by ultrasound on the upper arm and thigh. The isokinetic strength of the elbow and knee extensor and flexor muscles were measured by an isokinetic dynamometer (Cybex 11) at 1.05 rad · s^–1. The women had significantly (P<0.001) larger fat CSA and smaller bone and muscle CSA than the men in both the upper arm and thigh. Among tissue CSA, the largest difference between the women and men was found in fat CSA regardless of the measurement sites. The sex differences in bone and muscle CSA were found largely in the upper arm compared to the thigh, even when expressed per unit second power of the limb length. Regression analyses of the data for respective samples for the men and women showed significant correlations (r=0.411–0.707, P < 0.05–P < 0.001) between CSA and strength in all muscle groups except for the elbow extensors of the men (r=0.328, P>0.05) and the elbow flexors of the women (r=0.388, P>0.05). No significant difference between sexes was observed when strength was expressed per unit of muscle CSA (F · CSA^–1) for the elbow flexors and extensors. However, the men showed significantly higher F · CSA^–1 than the women for the knee flexors and extensors (P < 0.001). These results would indicate that, although the difference between sexes in muscle CSA is smaller in the thigh than in the upper arm, differences in the ability to develop dynamic strength proportional to the CSA appeared mainly in the thigh muscles compared to the upper muscles.     

Quantitating the capillary supply and the response to resistance training in older men

 Resistance training (RT) has been shown to increase aerobic power in older humans. To determine the effects of RT on the capillary supply in this population, nine older men (65–74 y) engaged in 9 weeks RT of the lower body. Following RT, peak O₂ uptake (V.O_2,peak) increased by 7% (P<.01). Needle biopsies (vastus lateralis muscle) revealed significant increases (mean ± SE) in fibre area (3,874 ± 314 μm² to 4,778 ± 309 μm²), fibre perimeter (P, 262 ± 11 μm to 296 ± 11 μm), capillary contacts (3.7 ± .2 to 4.3 ± .3) and the individual capillary-to-fibre ratio (C:F_i, 1.33 ± .32 to 1.61 ± .37, P<.005). To evaluate the potential for blood-tissue exchange, both fibre area-based and perimeter-based measures of the capillary supply were compared. While the area-based measures were maintained, C:F_i/P was increased, consistent with an increase in the size of the fibre-capillary interface and thus, an increased potential for oxygen flux following RT. Of the measurements of capillary supply, V.O_2,peak correlated best with C:F_i/P (r = 0.69, P<.005). These results indicate a significant increase in the capillary supply relative to the perimeter, but not the cross-sectional area, of the muscle fibres following RT in older men, and that C:F_i/P is strongly correlated to the V.O_2,peak in this population. Received: 25 April 1996 / Received after revision: 16 August 1996 / Accepted: 20 August 1996     

Modelling of aerobic and anaerobic energy production during exhaustive exercise on a cycle ergometer

An extension of the original hyperbolic model (Model-2) was proposed by using power output required to elicit maximal oxygen uptake (P _t). This study aimed to test this new model (Model-α) using mechanical work produced during cycle ergometry. Model α assumed that power exceeding a critical power (P _c) was met partly by the anaerobic metabolism. The parameter α was the proportion of the power exceeding P _c provided by anaerobic metabolism, while power exceeding P _t was exclusively met by anaerobic metabolism. Aerobic power was assumed to rise monoexponentially with a time constant τ. The exhaustion was assumed to be reached when the anaerobic work capacity W′ was entirely utilised. Twelve subjects performed one progressive ramp test to assess the power at ventilatory threshold (P _VT) and P _t and five constant-load exercise to exhaustion within 2–30 min, with one to estimate the maximal accumulated oxygen deficit (MAOD). Parameters from Model α were fitted with τ equal to 0, 10, 20 and 30 s. Results in goodness-of-fit was better than Model-2 whatever the value assumed for τ (P < 0.05). The value of τ did not affect much the estimates for P _c and α. P _c estimates were significantly correlated with P _c from Model-2 and with P _VT. W′ estimates, which were dependent on the value ascribed to τ, were not statistically different than MAOD. These two variables were, however, not significantly correlated. In conclusion, Model α could provide useful information on the critical power and the anaerobic contribution according to exercise intensity, whereas W′ estimates should be used with care because of the sensitivity to the assumption on aerobic power kinetics τ.     

Decline in isokinetic force with age: muscle cross-sectional area and specific force

 Humans produce less muscle force (F) as they age. However, the relationship between decreased force and muscle cross-sectional area (CSA) in older humans is not well documented. We examined changes in F and CSA to determine the relative contributions of muscle atrophy and specific force (F/CSA) to declining force production in aging humans. The proportions of myosin heavy chain (MHC) isoforms were characterized to assess whether this was related to changes in specific force with age. We measured the peak force of isokinetic knee extension in 57 males and females aged 23–80 years, and used magnetic resonance imaging to determine the contractile area of the quadriceps muscle. Analysis of MHC isoforms taken from biopsies of the vastus lateralis muscle showed no relation to specific force. F, CSA, and F/CSA decreased with age. Smaller CSA accounted for only about half of the 39% drop in force that occurred between ages 65–80 years. Specific force dropped about 1.5% per year in this age range, for a total decrease of 21%. Thus, quantitative changes in muscle (atrophy) are not sufficient to explain the strength loss associated with aging. Received: 12 November 1996 / Received after revision: 10 March 1997 / Accepted: 19 March 1997     

Determination of critical power in trained rowers using a three-minute all-out rowing test

The purpose of this study was to determine whether the hyperbolic relationship between power output and time to exhaustion (work − time and power − [1/time] models) could be estimated from a modified version of a three-minute all-out rowing test (3-min RT), and to investigate the test–retest reliability of the 3-min RT. Eighteen male rowers volunteered to participate in this study and underwent an incremental exercise test (IRT), three constant-work rate tests to establish the critical power (CP) and the curvature constant (W′), and two 3-min RTs against a fixed resistance to estimate the end-test power (EP) and work-done-above-EP (WEP) on a rowing ergometer. Peak ( [(V)\dot]\textO _{2 \textpeak} ) \left( {\dot{V}{\text{O}}_{{ 2 {\text{peak}}}} } \right) and maximal ( [(V)\dot]\textO_2max ) \left( {\dot{V}{\text{O}}_{2\max } } \right) oxygen uptakes were calculated as the highest 30 s average achieved during the 3-min RT and IRT tests. The results showed that EP and WEP determinations, based on the 3-min RT, have moderate reproducibility (P = 0.002). EP (269 ± 39 W) was significantly correlated with CP (work − time, 272 ± 30 W; power − [1/time], 276 ± 32 W) (P = 0.000), with no significant differences observed between the EP and CP values (P = 0.474). However, WEP did not significantly correlate with W′ (P = 0.254), and was significantly higher than the W′ values. There was a significant correlation between the [(V)\dot]\textO _{2 \textpeak} \dot{V}{\text{O}}_{{ 2 {\text{peak}}}} (60 ± 3 ml kg⁻¹ min⁻¹) and [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (61 ± 4 ml kg⁻¹ min⁻¹) (P = 0.003). These results indicate that the 3-min RT has moderate reliability, and is able to appropriately estimate the aerobic capacity in rowers, particularly for the CP and [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } parameters.     

Changes in lower limb muscle cross-sectional area and tissue fluid volume after transition from standing to supine

Lower limbs show acute fluid shift in response to transition from upright to supine body position. It is hypothesized that this would affect tomographic estimations of muscle mass and composition. Seven healthy subjects were investigated during the initial 120 min of bed rest, using repeated computerized tomography (CT) and continuous bioelectrical impedance analysis (BIA). Thigh and calf muscle cross-sectional area (CSA) decreased (P < 0.05) by 1.9 and 5.5% whereas fat CSA decreased (P < 0.05) by 4.1 and 4.4%, respectively. Radiological density (RD) of muscle showed a simultaneous increase (P < 0.05) by 4.8% in calf but not (P > 0.05) in thigh. No changes occurred (P > 0.05) in muscle or fat CSA or muscle RD in either thigh or calf between the first and second hour of bed rest. Fluid shift, as estimated by BIA, showed an exponential decay in thigh (τ_th = 30 min) and calf (τ_c2 = 37 min) by 2.5 and 8.7%, respectively, from first to 120 min of bed rest. Moreover, the calf showed an initial rapid (τ_c1 = 8 s) 2.2% decrease. The demonstrated short-term changes in leg CSA were more pronounced in the calf than in the thigh. They were similar in muscle and subcutaneous fat. These fluid shifts merit consideration when tomographic imaging techniques are used to estimate muscle mass and composition.     

Estimating transit time for capillary blood in selected muscles of exercising animals

The mean minimal capillary transit time was estimated in muscles of various animals using a combination of physiological and morphometric methods. Radioactive microspheres were injected intravascularly in various animals running on a treadmill at maximum oxygen consumption rate (VO_2,max) to label blood flow to individual muscles. The muscles were then removed and preserved by standard methods for electron microscopy. The volume density of mitochondria was measured to assess muscle oxidative capacity. Capillary densities in muscle cross-sections, capillary diameters and tortuosities were incorporated into an estimate of capillary volume per unit muscle mass. Mean capillary transit time (t _c) in the exercising muscles was estimated by dividing mass-specific capillary volume by mass-specific blood flow. Estimates of t _c ranged from values near 1 s in horse heart and thigh muscles to 0.2 s in duck gastrocnemius. The relationship between muscle blood flow and t _c was hyperbolic. The experimental data indicate a limiting value of 0.2 s for transit times at very high blood flows. There was no correlation between t _c and body-mass-specific VO_2,max.     

Leg extensor power and dehydroepiandrosterone sulfate, insulin-like growth factor-I and testosterone in healthy active elderly people

We examined the association between quadriceps muscle function and serum levels of dehydroepiandrosterone sulphate (DHEAS), insulin-like growth factor I (IGF-I) and testosterone in a group of healthy elderly people. Fifty-three independent, community-dwelling elderly subjects (26 men and 27 women) aged from 66 to 84 years volunteered to participate in the study. Physical activity (PA) was evaluated by a questionnaire. Quadriceps maximal muscle power (W˙ _max) and optimal shortening velocity (v _opt) were measured on a friction-loaded non-isokinetic cycle ergometer. The W˙ _max is expressed in relation to body mass (W˙ _max/kg, W · kg⁻¹), and in relation to the mass of the two quadriceps muscles (W˙ _max/Quadr, W · kg_Quadr ⁻¹). In women, when adjusted for age, anthropometric measurements and PA indices, IGF-I correlated significantly with W˙ _max/kg (partial correlation: r=0.59; P=0.001), W˙ _max/Quadr (r=0.58; P=0.002) and v _opt (r=0.53; P=0.004), whereas DHEAS was correlated significantly with W˙ _max/kg (r=0.54; P=0.003) and W˙ _max/Quadr (r=0.58; P=0.002). No such correlation was found in men. These findings indicate that in healthy elderly women lower values for quadriceps muscle W˙ _max and v _opt are related, independently of age, anthropometric measurements and PA indices, to lower circulating levels of DHEAS and IGF-I. Accepted: 29 December 1999     

Physiological responses that account for the increased power output in speed skating using klapskates

The present study investigates which physiological sources support the increase in mechanical power output (W˙ _out) that can be obtained using klapskates in speed skating. It was hypothesized that the increase in W˙ _out could be achieved through an increase in gross efficiency or an increase in aerobic power (W˙ _aer). Six speed skaters performed a submaximal and maximal 1600-m skating test with both klapskates and conventional skates, to measure gross efficiency and maximal W˙ _aer during speed skating. The rate of oxygen uptake (V˙O₂) and post-exercise blood lactate concentrations ([La]) were measured and video recordings were made. W˙ _aer was calculated from V˙O₂. W˙ _out was derived from the power needed to overcome air and ice friction. Gross efficiency was calculated as the ratio of W˙ _out and W˙ _aer. In the maximal tests, the subjects skated faster with klapskates compared to conventional skates (10.0 vs 9.6 m · s⁻¹). They sustained the resulting higher W˙ _out with klapskates with an equal V˙O₂. [La] was, however, 1.7 mmol · l⁻¹ higher when klapskates were used, which might reflect an increase in anaerobic power. During the submaximal tests the skaters generated equal W˙ _out with both types of skate. Although not statistically significant, V˙O₂ and W˙ _aer were, on average, lower when klapskates were used compared to conventional skates [mean (SD) 0.3 (0.43) l · min⁻¹, 105 (143) W]. Despite the lack of a statistically significant difference in W˙ _aer, gross efficiency was shown to be significantly higher with klapskates compared to conventional skates (16.3% vs 14.8%, P=0.02). We conclude that the increase in W˙ _out when the subjects were using klapskates could be explained by an increase in gross efficiency rather than an increase in W˙ _aer. Accepted: 20 July 2000     

Dynamic force responses of skeletal muscle during stretch–shortening cycles

Muscle damage due to stretch–shortening cycles (i.e., cyclic eccentric/concentric muscle actions) is one of the major concerns in sports and occupational related activities. Mechanical responses of whole muscle have been associated with damage in neural motor units, in connective tissues, and the force generation mechanism. The objective of this study was to introduce a new method to quantify the real-time changes in skeletal muscle forces of rats during injurious stretch–shortening cycles. Male Sprague Dawley rats (n=24) were selected for use in this study. The dorsi flexor muscle group was exposed to either 150 stretch–shortening cycles (n=12) or 15 isometric contractions (n=12) in vivo using a dynamometer and electrical stimulation. Muscle damage after exposure to stretch–shortening cycles was verified by the non-recoverable force deficit at 48 h and the presence of myofiber necrosis. Variations of the dynamic forces during stretch–shortening cycles were analyzed by decomposing the dynamic force signature into peak force (F_peak), minimum force (F_min), average force (F_mean), and cyclic force (F_a). After the 15th set of stretch–shortening cycles, the decrease in the stretch–shortening parameters, F_peak, F_min, F_mean, and F_a, was 50% (P<0.0001), 26% (P=0.0055), 68% (P<0.0001), and 50% (P<0.0001), respectively. Our results showed that both isometric contractions and stretch–shortening cycles induce a reduction in the isometric force. However, the force reduction induced by isometric contractions fully recovered after a break of 48 h while that induced by stretch–shortening cycles did not. Histopathologic assessment of the tibialis anterior exposed to stretch–shortening cycles showed significant myofiber degeneration and necrosis with associated inflammation, while muscles exposed to isometric contractions showed no myofiber degeneration and necrosis, and limited inflammation. Our results suggest that muscle damage can be identified by the non-recoverable isometric force decrement and also by the variations in the dynamic force signature during stretch–shortening cycles.     

In-season strength maintenance training increases well-trained cyclists’ performance

We investigated the effects of strength maintenance training on thigh muscle cross-sectional area (CSA), leg strength, determinants of cycling performance, and cycling performance. Well-trained cyclists completed either (1) usual endurance training supplemented with heavy strength training twice a week during a 12-week preparatory period followed by strength maintenance training once a week during the first 13 weeks of a competition period (E + S; n = 6 [♂ = 6]), or (2) usual endurance training during the whole intervention period (E; n = 6 [♂ = 5, ♀ = 1]). Following the preparatory period, E + S increased thigh muscle CSA and 1RM (p < 0.05), while no changes were observed in E. Both groups increased maximal oxygen consumption and mean power output in the 40-min all-out trial (p < 0.05). At 13 weeks into the competition period, E + S had preserved the increase in CSA and strength from the preparatory period. From the beginning of the preparatory period to 13 weeks into the competition period, E + S increased peak power output in the Wingate test, power output at 2 mmol l⁻¹ [la⁻], maximal aerobic power output (W _max), and mean power output in the 40-min all-out trial (p < 0.05). The relative improvements in the last two measurements were larger than in E (p < 0.05). For E, W _max and power output at 2 mmol l⁻¹ [la⁻] remained unchanged. In conclusion, in well-trained cyclists, strength maintenance training in a competition period preserved increases in thigh muscle CSA and leg strength attained in a preceding preparatory period and further improved cycling performance determinants and performance.     

Effects of different after-loads and knee angles on maximal explosive power of the lower limbs in humans

Maximal explosive power during two-leg jumps was measured on four sedentary subjects [mean age 43.0 (SD 10.3) years, mean height 1.74 (SD 0.04) m, mean body mass 73.5 (SD 1.3) kg] using a sledge apparatus with which both force and speed could be directly measured. Different after-loads were obtained by positioning the sledge at five different angles (SA, α) in respect to the horizontal so that m · g · sin α (where m is the sum of body mass and the mass of the sledge seat, g the acceleration due to gravity) decreased (on average) from 78% body mass at 30° to 27% body mass at 10°, thus simulating conditions of low gravity. The subjects were asked to jump maximally, without counter movement, starting from 70°, 90°, 110°, and 140° of knee angle (KA); the protocol being repeated at 10°, 15°, 20°, 25° and 30° SA. The average (W˙ _mean ⁺) power output during concentric exercise (CE) was found to decrease when the starting KA was increased, but to be unaffected by SA (i.e. by the after-load, the simulated low g). The higher values of W˙ _mean ⁺ were recorded at 90° KA [15.01 (SD 1.46) W · kg⁻¹, average for all subjects at all SA]. The subjects were also asked to perform counter movement (CMJ) and rebound jumps (RE) at the same SA as for CE. In CMJ and RE maximal power outputs were also found to be unaffected by the SA; W˙ _mean ⁺ amounted to 16.03 (SD 0.28) W · kg⁻¹ in CMJ and 16.88 (SD 0.36) W · kg⁻¹ in RE (average for all subjects at all SA). In CE, CMJ and RE, the instantaneous force at the onset of the positive speed phase (F _i) was found to increase linearly with SA (i.e. with increasing m · g · sin α), and the difference between F _i in CMJ or RE and F _i in CE (F _i in CMJ minus F _i in CE and F _i in RE minus F _i in CE) was unaffected by SA. This indicated that both maximal power and the elastic recoil were unaffected by simulated low g ranging from 1.71 m · s⁻² (at 10° SA) to 4.91 m · s⁻² (at 30° SA). Accepted: 9 March 2000     

Cardiorespiratory responses to exercise in acute hypoxia, hyperoxia and normoxia

There is a prevailing hypothesis that an acute change in the fraction of oxygen in inspired air (F _IO₂) has no effect on maximal cardiac output ( ), although maximal oxygen uptake ( ) and exercise performance do vary along with F _IO₂. We tested this hypothesis in six endurance athletes during progressive cycle ergometer exercise in conditions of hypoxia (F _IO₂=0.150), normoxia (F _IO₂=0.209) and hyperoxia (F _IO₂=0.320). As expected, decreased in hypoxia [mean (SD) 3.58 (0.45) l·min^–1, P<0.05] and increased in hyperoxia [5.17 (0.34) l·min^–1, P<0.05] in comparison with normoxia [4.55 (0.32) l·min^–1]. Similarly, maximal power ( ) decreased in hypoxia [334 (41) W, P<0.05] and tended to increase in hyperoxia [404 (58) W] in comparison with normoxia [383 (46) W]. Contrary to the hypothesis, was 25.99 (3.37) l·min^–1 in hypoxia (P<0.05 compared to normoxia and hyperoxia), 28.51 (2.36) l·min^–1 in normoxia and 30.13 (2.06) l·min^–1 in hyperoxia. Our results can be interpreted to indicate that (1) the reduction in in acute hypoxia is explained both by the narrowing of the arterio-venous oxygen difference and reduced , (2) reduced in acute hypoxia may be beneficial by preventing a further decrease in pulmonary and peripheral oxygen diffusion, and (3) reduced and in acute hypoxia may be the result rather than the cause of the reduced and skeletal muscle recruitment, thus supporting the existence of a central governor. Electronic Publication     

Influence of cerebral and muscle oxygenation on repeated-sprint ability

The study examined the influence of cerebral (prefrontal cortex) and muscle (vastus lateralis) oxygenation on the ability to perform repeated, cycling sprints. Thirteen team-sport athletes performed ten, 10-s sprints (with 30 s of rest) under normoxic (F_IO₂ 0.21) and acute hypoxic (F_IO₂ 0.13) conditions in a randomised, single-blind fashion and crossover design. Mechanical work was calculated and arterial O₂ saturation (S_pO₂) was estimated via pulse oximetry for every sprint. Cerebral and muscle oxy-(O₂Hb), deoxy-(HHb), and total haemoglobin (THb) were monitored continuously by near-infrared spectroscopy. Compared with normoxia, hypoxia induced larger decrements in S_pO₂ and work (11.6 and 7.6%, respectively; P < 0.05). In the muscle, we observed a fairly constant level of deoxygenation across sprints, with no effect of the condition. In normoxia, regional cerebral oxygenation increased during the first two sprints and slightly fluctuated thereafter. In contrast, this initial cerebral hyper-oxygenation was attenuated in hypoxia. Changes in [O₂Hb] and [HHb] occurred earlier and were larger in hypoxia compared with normoxia (P < 0.05), while regional blood volume (Δ[THb]) remained unaffected by the condition. Changes in cerebral [HHb] and mechanical work were strongly correlated in normoxia and hypoxia (R ² = 0.81 and R ² = 0.85, respectively; P < 0.05), although the slope of this relationship differed (normoxia, −351.3 ± 183.3 vs. hypoxia, −442.4 ± 227.2; P < 0.05). The results of this NIRS study show that O₂ availability influences prefrontal cortex, but not muscle, oxygenation during repeated, short sprints. By using a hypoxia paradigm, the study suggests that cerebral oxygenation contributes to the impairment of repeated-sprint ability.     

In vivo specific tension of the human quadriceps femoris muscle

It is not known to what extent the inter-individual variation in human muscle strength is explicable by differences in specific tension. To investigate this, a comprehensive approach was used to determine in vivo specific tension of the quadriceps femoris (QF) muscle (Method 1). Since this is a protracted technique, a simpler procedure was also developed to accurately estimate QF specific tension (Method 2). Method 1 comprised calculating patellar tendon force (F _t) in 27 young, untrained males, by correcting maximum voluntary contraction (MVC) for antagonist co-activation, voluntary activation and moment arm length. For each component muscle, the physiological cross-sectional area (PCSA) was calculated as volume divided by fascicle length during MVC. Dividing F _t by the sum of the four PCSAs (each multiplied by the cosine of its pennation angle during MVC) provided QF specific tension. Method 2 was a simplification of Method 1, where QF specific tension was estimated from a single anatomical CSA and vastus lateralis muscle geometry. Using Method 1, the variability in MVC (18%) and specific tension (16%) was similar. Specific tension from Method 1 (30 ± 5 N cm⁻²) was similar to and correlated with that of Method 2 (29 ± 5 N cm⁻²; R ² = 0.67; P < 0.05). In conclusion, most of the inter-individual variability in MVC torque remains largely unexplained. Furthermore, a simple method of estimating QF specific tension provided similar values to the comprehensive approach, thereby enabling accurate estimations of QF specific tension where time and resources are limited.     

Surface electromyograms of agonist and antagonist muscles during force development of maximal isometric exercises—effects of instruction

Surface integrated electromyograms (iEMG) of agonist and antagonist muscles were studied during the rising phase of maximal isometric efforts (elbow flexion, unilateral and bilateral leg extension) to explain the difference in maximal rate of force development (MRFD) with a hard-and-fast instruction (instruction I) and a fast instruction (instruction II ). Force and EMG were simultaneously recorded in 24 athletes and iEMG were computed at MRFD and during different phases of force development (P _0–25, P _25–50, P _50–75, P _75–90 and P _90–100). A two-way ANOVA for repeated measures (muscle × instruction) showed that the value of iEMG at MRFD was significantly higher with instruction II for elbow flexion, unilateral and bilateral leg press exercises (F>4.9; P<0.04). The effect of instruction upon iEMG of the agonist muscles corresponding to the different phases of the force development was significant for elbow flexion (F=4.2;P<0.05 ) unilateral (F>6.4; P<0.02) and bilateral leg extension (F>9 and P<0.006 for soleus and vastus lateralis; but F=3.2 and P=0.08 for vastus medialis). There was a significant interaction between instruction and phase of force development (F>2.6; P<0.05 ): iEMG was significantly higher with instruction II at the beginning of force development (P _0–25) for all the muscles (except the soleus muscle during the bilateral leg exercise) but not at higher force (P _75–90 and P _90–100). The steeper force development with instruction II can be explained by the better activation of the agonist muscles at the beginning of force development. A lower co-activation of the antagonist muscles does not explain the improvement in MRFD as the iEMG of the antagonist muscles was not lower with instruction II but was proportional to the activation level of the agonist muscle. Electronic Publication     

Selective training-induced thigh muscles hypertrophy in professional road cyclists

Muscular adaptations linked to a high volume and intensity of training have been scarcely reported. We aimed at documenting, using MRI, the cross-sectional area changes associated with a high volume and intensity of training in 11 thigh muscles of a population of professional road cyclists as compared with sport science students. We were also interested in determining, whether selective muscle hypertrophy in professional road cyclists, if any, was correlated to selective exercise-induced T ₂ changes during a pedaling exercise on a cycloergometer. Cross-sectional area of 11 thigh muscles was quantified in sixteen subjects (i.e. eight professional road cyclists and eight sport science students) using MRI. In addition, transverse relaxation times (T ₂) were measured before and just after a maximal standardized constant-load exercise in order to investigate exercise-related T ₂ changes in these muscles. Professional road cyclists had a significantly higher relative amount of muscle (including the whole set of thigh muscles, 90.5±3.3%) as compared to controls (81.6±7.3%). Regarding relative values expressed with respect to the total thigh muscles CSA, Vastus lateralis and Biceps femoris CSA were significantly larger in cyclists whereas CSA of the Vastus intermedius was smaller. However, this selective hypertrophy was not correlated to the exercise-induced T ₂-increase. We have reported, for the first time, a selective hypertrophy of Vastus lateralis and Biceps femoris in professional road cyclists confirming their involvement in pedaling task and suggesting a possible cause–effect relationship between muscle activation and hypertrophy, associated with a specific pedaling skill.