THE RELATIONSHIP BETWEEN MAXIMAL AND EXPLOSIVE VOLUNTARY MUSCULAR TORQUE AND THE RESPONSE TO UNEXPECTED PERTURBATIONS

The purpose of this study was to investigate the relationship between explosive toque of the plantar flexors and knee extensors and the centre of mass (COM) response to unexpected perturbations. 17 subjects were assessed for maximal and explosive isometric knee extension (KE) and plantar flexion (PF) toque and their response to unexpected anterior platform translations. The relationships between these measures were investigated using Pearson's correlation coefficients. Explosive torque of KE at 25 and 50 ms and PF at 50 and 75 ms demonstrated significant negative correlations (r = -0.528 to -0.575, p < 0.05) with COM acceleration at 300 ms post perturbation. This suggests that the ability to produce torque rapidly could assist in reducing and reversing the imposed COM acceleration following an unexpected perturbation

Contraction speed and type influences rapid utilisation of available muscle force:neural and contractile mechanisms

This study investigated the influence of contraction speed and type on the human ability to rapidly increase torque and utilise the available maximum voluntary torque (MVT) as well as the neuromuscular mechanisms underpinning any effects. Fifteen young, healthy males completed explosive-voluntary knee-extensions in five conditions: isometric (ISO), and both concentric and eccentric at two constant accelerations of 500°.s-2 (CONSLOW and ECCSLOW) and 2000°.s-2 (CONFAST and ECCFAST). Explosive torque and quadriceps EMG were recorded every 25 ms up to 150 ms from their respective onsets and normalised to the available MVT and EMG at MVT, respectively, specific to that joint angle and velocity. Neural efficacy (explosive Voluntary:Evoked octet torque) was also measured, and torque data were entered into a Hill-type muscle model to estimate muscle performance. Explosive torques normalised to MVT (and normalised muscle forces) were greatest in the concentric, followed by isometric, and eccentric conditions; and in the fast compared with slow speeds within the same contraction type (CONFAST>CONSLOW>ISO, and ECCFAST>ECCSLOW). Normalised explosive-phase EMG and neural efficacy were greatest in concentric, followed by isometric and eccentric conditions, but were similar for fast and slow contractions of the same type. Thus, distinct neuromuscular activation appeared to explain the effect of contraction type but not speed on normalised explosive torque, suggesting the speed effect is an intrinsic contractile property. These results provide novel evidence that the ability to rapidly increase torque/force and utilise the available MVT is influenced by both contraction type and speed, due to neural and contractile mechanisms, respectively

Influence of crank length and crank-axle height on standing arm-crank (grinding) power

To determine the optimal crank length and crank-axle height for maximum power production during standing arm-cranking (‘grinding’). Nine elite professional America’s Cup grinders (age: 36 ± 2 y; body mass: 104 ± 1 kg; body fat 13 ± 2%) performed eight maximal 6 s sprints on an adjustable standing arm-crank ergometer fitted with an SRM powercrank. The protocol included crank lengths of 162, 199, 236 and 273 mm and crank-axle heights of 850, 950, 1050 and 1150 mm. Peak power, ground reaction forces (GRF) and joint angles were determined and compared for different crank lengths and crank-axle heights with repeated-measures ANOVA. Results: Peak power was significantly different between crank lengths (P=0.006), with 162 mm lower than all others (P<0.03). Optimal crank length was 12.3% of arm-span, or 241 ± 9 mm for this cohort of athletes. Peak power was significantly less for the crank-axle height of 850 mm compared to 1150 mm (P=0.01). The optimal crank-axle height for peak power was between 50 and 60% of stature (950-1150 mm in this study). Hip flexion was greater at the lowest crank-axle height (850 mm) than at 1050 and 1150 mm (P<0.01), and the resultant GRF was also reduced compared to all other heights, indicating greater weight bearing by the upper body. Changes in crank length and crank-axle height influence performance during maximal standing arm-crank ergometry. These results, suggest that standard leg-cycle crank lengths are inappropriate for maximal arm-cranking performance. In addition, a crank-axle height of <50% of stature, which is typically used in America’s Cup sailing, may attenuate performance

Explosive voluntary torque is related to whole-body response to unexpected perturbations

Explosive torque has been demonstrated to relate to static balance. However, sports injuries occur dynamically and unpredictably, yet the relationship between explosive torque and balance response to dynamic perturbations is unknown. This study investigated the relationship between explosive torque of the plantar flexors and knee extensors and the centre of mass (COM) response to unexpected perturbations. Thirty-three healthy subjects (17 females, 16 males) were assessed for maximal and explosive isometric knee extension (KE) and plantar flexion (PF) torque and COM response (velocity (COMV), displacement (COMD)) to unexpected platform translations. Relationships between explosive torque and balance measures were investigated using Pearson's correlation and multiple regression. A negative relationship between PF explosive torque at 50, 100, and 150 ms and COMV at 300, 400, and 500 ms (r = −0.363 to −0.508, p ≤ 0.049), and COMD at 400 and 500 ms (r = −0.349 to −0.416, p ≤ 0.046) was revealed. A negative relationship between KE explosive torque at 50, 100, and 150 ms and COMV at 400 ms (r = −0.381 to −0.411, p ≤ 0.029) but not COMD was also revealed. Multiple regression found PF 100 ms predicted 17.3% of variability in COMD at 500 ms and 25.8% of variability in COMV at 400 ms. These results suggest that producing torque rapidly may improve COM response to unexpected perturbation

Aerobic power and peak power of elite America’s Cup sailors

Big-boat yacht racing is one of the only able bodied sporting activities where standing armcranking (‘grinding’) is the primary physical activity. However, the physiological capabilities of elite sailors for standing arm-cranking have been largely unreported. The purpose of the study was to assess aerobic parameters, VO2peak and lactate threshold (OBLA), and anaerobic performance, torque- and power-crank velocity relationships and therefore peak power (Pmax) and optimum crank-velocity (ωopt), of America’s Cup sailors during standing arm-cranking. Thirty-three elite professional sailors performed a step test to exhaustion, and a subset of ten grinders performed maximal 7 s isokinetic sprints at different crank velocities, using a standing arm-crank ergometer. VO2peak was 4.7(0.5) L/min (range: 3.6-5.5 L/min) at a power output of 332(44) W (range: 235- 425 W). OBLA occurred at a power output of 202(31) W (61% of Wmax) and VO2 of 3.3(0.4) L/min (71% of VO2peak). The torque-crank velocity relationship was linear for all participants (r=0.9(0.1)). Pmax was 1420(37) W (range: 1192-1617 W), and ωopt was 125(6) rpm. These data are among the highest upper-body anaerobic and aerobic power values reported. The unique nature of these athletes, with their high fat-free mass and specific selection and training for standing arm cranking, likely accounts for the high values. The influence of crank velocity on peak power implies that power production during on-board ‘grinding’ may be optimised through the use of appropriate gear-ratios and the development of efficient gear change mechanisms

Explosive strength: effect of knee-joint angle on functional, neural, and intrinsic contractile properties

PURPOSE: The present study compared knee extension explosive isometric torque, neuromuscular activation, and intrinsic contractile properties at five different knee-joint angles (35°, 50°, 65°, 80°, and 95°; 0° = full knee extension). METHODS: Twenty-eight young healthy males performed two experimental sessions each involving: 2 maximum, and 6-8 explosive voluntary contractions at each angle; to measure maximum voluntary torque (MVT), explosive voluntary torque (EVT; 50-150 ms after contraction onset) and quadriceps surface EMG (QEMG, 0-50, 0-100, and 0-150 ms after EMG onset during the explosive contractions). Maximum twitch and M-wave (MMAX) responses as well as octet contractions were evoked with femoral nerve stimulation at each angle. RESULTS: Absolute MVT and EVT showed an inverted 'U' relationship with higher torque at intermediate angles. There were no differences between knee-joint angles for relative EVT (%MVT) during the early phase (≤ 75 ms) of contraction and only subtle differences during the late phase (≥ 75 ms) of contraction (≤ 11%). Neuromuscular activation during explosive contractions was greater at more flexed than extended positions, and this was also the case during MVT. Whilst relative twitch torque (%MVT) was higher at knee flexed positions (P ≤ 0.001), relative octet torque (%MVT) was higher at knee extended positions (P ≤ 0.001). CONCLUSION: Relative EVT was broadly similar between joint angles, likely because neuromuscular activation during both explosive and plateau (maximum) phases of contraction changed proportionally, and due to the opposing changes in twitch and octet evoked responses with joint angle

Sex differences in muscle morphology of the knee flexors and knee extensors

Introduction Females experience higher risk of anterior cruciate ligament (ACL) injuries; males experience higher risk of hamstring strain injuries. Differences in injury may be partially due to sex differences in knee flexor (KF) to knee extensor (KE) muscle size ratio and the proportional size of constituent muscles. Purpose To compare the absolute and proportional size, and mass distribution, of individual KE and KF muscles, as well as overall size and balance (size ratio) of these muscle groups between the sexes. Methods T1-weighted axial plane MR images (1.5T) of healthy untrained young males and females (32 vs 34) were acquired to determine thigh muscle anatomical cross-sectional area(ACSA). Maximal ACSA (ACSAmax) ofconstituent muscles, summated for KF and KE muscle groups, and the KF:KE ratio were calculated. Results Females had 25.3% smaller KE ACSAmax (70.9±12.1 vs 93.6±10.3 cm2; P<0.001) and 29.6% smaller KF ACSAmax than males (38.8±7.3cm2 vs 55.1±7.3cm2; P<0.001).Consequently, females had lower KF:KE ACSA ratio (P = 0.031). There were sex differences in the proportional size of 2/4 KE and 5/6 KF. In females, vastus lateralis (VL), biceps femoris long-head (BFlh) and semimembranosus (SM) were a greater proportion and sartorius(SA), gracilis (GR) and biceps femoris short-head (BFsh) a smaller proportion of their respective muscle groups compared to males (All P<0.05). Conclusion Sex differences in KF:KE ACSAmax ratio may contribute to increased risk of ACL injury in females. Sex discrepancies in absolute and proportional size of SA, GR, VL and BFlh may contribute further anatomical explanations for sex differences in injury incidence

The efficacy of downhill running as a method to enhance running economy in trained distance runners

© 2018 European College of Sport Science Running downhill, in comparison to running on the flat, appears to involve an exaggerated stretch-shortening cycle (SSC) due to greater impact loads and higher vertical velocity on landing, whilst also incurring a lower metabolic cost. Therefore, downhill running could facilitate higher volumes of training at higher speeds whilst performing an exaggerated SSC, potentially inducing favourable adaptations in running mechanics and running economy (RE). This investigation assessed the efficacy of a supplementary 8-week programme of downhill running as a means of enhancing RE in well-trained distance runners. Nineteen athletes completed supplementary downhill (−5% gradient; n = 10) or flat (n = 9) run training twice a week for 8 weeks within their habitual training. Participants trained at a standardised intensity based on the velocity of lactate turnpoint (vLTP), with training volume increased incrementally between weeks. Changes in energy cost of running (E C ) and vLTP were assessed on both flat and downhill gradients, in addition to maximal oxygen uptake (⩒O 2max). No changes in E C were observed during flat running following downhill (1.22 ± 0.09 vs 1.20 ± 0.07 Kcal kg −1  km −1 , P = .41) or flat run training (1.21 ± 0.13 vs 1.19 ± 0.12 Kcal kg −1  km −1 ). Moreover, no changes in E C during downhill running were observed in either condition (P  >  .23). vLTP increased following both downhill (16.5 ± 0.7 vs 16.9 ± 0.6 km h −1 ,P = .05) and flat run training (16.9 ± 0.7 vs 17.2 ± 1.0 km h −1 , P = .05), though no differences in responses were observed between groups (P = .53). Therefore, a short programme of supplementary downhill run training does not appear to enhance RE in already well-trained individuals

Multidirectional hopping exercise improved balance and ankle plantarflexion strength in community-dwelling older men [Abstract]

Multidirectional hopping exercise improved balance and ankle plantarflexion strength in community-dwelling older men [Abstract