Relationship between jump height and lower limb joint kinetics and kinematics during countermovement jump in elite male athletes.

This study aims to identify the relationship between jump height and the kinetic and kinematic parameters of the hip, knee, and ankle joints during countermovement jump (CMJ) in elite male athletes. Sixty-six elite male athletes from various sports (strength and power, winter downhill, combat, ball game, and aquatic) performed maximal effort CMJs with hands and arms crossed against their chests on force platforms. Jumping motion in the sagittal plane was recorded using video analysis and the peak torque, power, and angular velocity of the right hip, knee, and ankle joints were calculated during the propulsive phase. Correlations between the CMJ height and kinetic and kinematic parameters were investigated using Pearson's product-moment coefficient (r) and Spearman's rank correlation coefficient (ρ). CMJ height was highly correlated with peak hip power (ρ = 0.686, p < 0.001) and peak knee angular velocity (r = 0.517, p < 0.001), and moderately correlated with peak hip angular velocity (r = 0.438, p < 0.001) and peak hip torque (r = 0.398, p = 0.001). These results indicate that notable hip torque and power can contribute to increased angular velocity in both the knee and hip joints, ultimately increasing the CMJ height in elite male athletes.

Physiological and Metabolic Responses to Low-Volume Sprint Interval Exercises: Influence of Sprint Duration and Repetitions.

PURPOSE: This study aimed to determine physiological and metabolic responses to two different sprint interval exercises (SIE) matched for total sprint duration and sprint-rest ratio. METHODS: After having measured peak oxygen uptake (V̇O 2peak ), 14 healthy males (27.1 ± 4.8 yr, 169.6 ± 6.0 cm, 64.5 ± 8.4 kg, V̇O 2peak : 47.2 ± 7.7 mL·kg -1 ·min -1 ) performed four 10-s sprints with 80-s recovery (SIE10) and two 20-s sprints with 160-s recovery (SIE20) on different occasions in a counterbalanced crossover manner. Pulmonary V̇O 2 and changes in tissue oxygenation index (∆TOI) at vastus lateralis (VL) and rectus femoris (RF) were measured during the SIE. Furthermore, T2-weighted magnetic resonance imaging was taken immediately before and after the SIE to determine the activation levels of VL, RF, vastus medialis, vastus intermedius, adductor magnus, biceps femoris long head, semitendinosus, and semimembranosus at 50% of right thigh length. RESULTS: In SIE10, increases in V̇O 2 and ∆TOI at VL and RF plateaued after the second sprint, whereas session-averaged ∆TOI was greater in SIE20 than SIE10 in both muscles (VL: 20.9 ± 7.4 vs 14.2% ± 5.9%, RF: 22.8 ± 9.3 vs 12.9% ± 6.6%, P = 0.00). Although both SIE significantly increased T2 values in all eight muscles, those magnitudes were similar between the conditions (SIE10 vs SIE20: 5%-16% vs 8%-16%). CONCLUSIONS: This study showed blunted responses of whole-body (V̇O 2 ) and peripheral (∆TOI) oxidative responses with successive sprints (sprint 1 < sprints 2-4) in SIE10, suggesting that increasing sprint repetitions does not necessarily induce greater oxidative metabolism or stimulus. Moreover, greater peripheral oxygen extraction (∆TOI) was achieved with SIE20, whereas %changes of T2 indicates that the thigh muscles were similarly activated between the SIE conditions.

Short-term repeated sprint training in hypoxia improves explosive power production capacity and repeated sprint ability in Japanese international-level male fencers: A case study.

This case study reports the effects of six sessions of repeated sprint training in hypoxia (RSH) over 3 weeks on explosive power production capacity and repeated sprint ability (RSA) in two Japanese international-level foil fencers. The six RSH sessions (60-s sprints in total per session: consisting of two sets of five 6-s sprints with 30-s passive recovery, at simulated altitude of 3000 m) caused improvements of peak power output (PPO; Athlete A: 5.1%; Athlete B: 3.2%) and mean power output (MPO; Athlete A: 4.4%; Athlete B: 1.6%) over the 10 repeated sprints, respectively. The observed findings suggest that as few as six RSH sessions over 3 weeks can improve, at least to some extent, explosive power production capacity (PPO) and RSA (MPO) in the two elite fencers. To the best of our knowledge, this is the first study to apply short-term RSH in combat sport (fencing) with international-level athletes. Further studies are required to explore the effectiveness of short-term RSH in combat sports with a more robust study design (e.g., randomized control trial with adequate statistical power) as the modality of RSH would suit physical and physiological demands in the majority of combat sports (e.g., wrestling, boxing).

Training cessation and subsequent retraining of a world-class female Olympic sailor after Tokyo 2020: A case study.

Olympic sailing is a complex sport where sailors are required to predict and interpret weather conditions while facing high physical and physiological demands. While it is essential for sailors to develop physical and physiological capabilities toward major competition, monitoring training status following the competition is equally important to minimize the magnitude of detraining and facilitate retraining. Despite its long history in the modern Olympics, reports on world-class sailors' training status and performance characteristics across different periodization phases are currently lacking. This case study aimed to determine the influence of training cessation and subsequent retraining on performance parameters in a world-class female sailor. A 31-year old female sailor, seventh in the Women's Sailing 470 medal race in Tokyo 2020, completely stopped training for 4 weeks following the Olympics, and resumed low-intensity training for 3 weeks. Over these 7 weeks, 12.7 and 5.3% reductions were observed in 6 s peak cycling power output and jump height, respectively, with a 4.7% decrease in maximal aerobic power output. Seven weeks of training cessation-retraining period induced clear reductions in explosive power production capacities but less prominent decreases in aerobic capacity. The current findings are likely attributed to the sailor's training characteristics during the retraining period.

Fatigue-induced changes in hamstrings' active muscle stiffness: effect of contraction type and implications for strain injuries.

PURPOSE: Hamstring strain injuries may occur due to differential fatigue and compromised mechanical properties among the hamstring muscles. We examined (1) the effect of fatigue on hamstrings active muscle stiffness, and (2) whether contraction type affects active muscle stiffness changes during a submaximal fatiguing task. METHODS: Nine healthy males completed 99 submaximal knee flexions in isometric (ISO), concentric (CON), and eccentric (ECC) conditions. We measured the knee flexor maximal voluntary torque (MVT) (pre/post), shear wave velocity (SWV) during contraction and transverse relaxation times (T2) (pre/post) in biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles. RESULTS: MVT decreased substantially after all conditions (- 18.4 to - 33.6%). The average relative torque sustained during the task was lower in CON than ISO and ECC, but absolute torque was similar. SWV interindividual responses were highly variable across muscles and contraction types. On average, BFlh SWV tended to increase in ISO (0.4 m/s, 4.5%, p = 0.064) but decreased in ECC condition (- 0.8 m/s, - 7.7%, p < 0.01). ST SWV decreased in CON (- 1.1 m/s, - 9.0%, p < 0.01), while it remained unchanged in ISO and ECC. SM SWV decreased in CON (- 0.8 m/s, - 8.1%, p < 0.01), but it was unaffected in ISO and variable in ECC. CONCLUSION: Fatigue has a differential effect on the mechanical properties of the constituent hamstring muscles, as measured with shear wave elastography, depending upon contraction type. We found preliminary evidence that BFlh is more fatigued than ST or SM during eccentric contractions, which may explain its susceptibility to strain injuries.

Determinants of whole-body maximal aerobic performance in young male and female athletes: The roles of lower extremity muscle size, strength and power.

This study sought to determine whether lower extremity muscle size, power and strength could be a determinant of whole-body maximal aerobic performance in athletes. 20 male and 19 female young athletes (18 ± 4 years) from various sporting disciplines participated in this study. All athletes performed a continuous ramp-incremental cycling to exhaustion for the determination of peak oxygen uptake ([Formula: see text]: the highest [Formula: see text] over a 15-s period) and maximal power output (MPO: power output corresponding to [Formula: see text]). Axial scanning of the right leg was performed with magnetic resonance imaging, and anatomical cross-sectional areas (CSAs) of quadriceps femoris (QF) and hamstring muscles at 50% of thigh length were measured. Moreover, bilateral leg extension power and unilateral isometric knee extension and flexion torque were determined. All variables were normalised to body mass, and six independent variables ([Formula: see text], CSAs of thigh muscles, leg extension power and knee extension and flexion torque) were entered into a forward stepwise multiple regression model with MPO being dependent variable for males and females separately. In the males, [Formula: see text] was chosen as the single predictor of MPO explaining 78% of the variance. In the females, MPO was attributed to, in the order of importance, [Formula: see text] (p < 0.001) and the CSA of QF (p = 0.011) accounting for 84% of the variance. This study suggests that while oxygen transport capacity is the main determinant of MPO regardless of sex, thigh muscle size also has a role in whole-body maximal aerobic performance in female athletes.

Investigation of the association between human fascia lata thickness and its neighboring tissues' morphology and function using B-mode ultrasonography.

The fascia lata is a membrane tissue which envelopes all thigh muscles and connects with the subcutaneous adipose tissues through loose connective tissues. It is presumable that the morphology of the fascia lata is strongly affected by the unique properties of underlying thigh muscles and subcutaneous adipose tissues. We aimed to investigate the relationships between characteristics of the fascia lata and adjoining adipose tissues and underlying muscles. Twenty healthy people were recruited (25 ± 3 years, 167.1 ± 8.5 cm, 62.5 ± 13.2 kg). The thickness of the skeletal muscles (rectus femoris, vastus lateralis, biceps femoris, and semitendinosus), and their overlying fascia lata and subcutaneous adipose tissues were measured by B-mode ultrasonography. Isometric knee extension and flexion torque during maximal voluntary contraction were also tested. The fascia lata thickness demonstrated site-dependent differences (vastus lateralis: 0.91 ± 0.20 mm > rectus femoris, biceps femoris, and semitendinosus: 0.56-0.69 mm, p < 0.01). Furthermore, there were large individual variations in the fascia lata thickness even in the same region of the thigh. The fascia lata showed positive simple correlations with height (rectus femoris: r = 0.39 p = 0.01, semitendinosus: r = 0.37 p < 0.05), body mass (rectus femoris: r = 0.59, p < 0.01, vastus lateralis: r = 0.47, p < 0.01, semitendinosus: r = 0.55, p < 0.01), corresponding muscle thickness (rectus femoris: r = 0.39, p < 0.05, semitendinosus: r = 0.74, p < 0.01) and knee extension (rectus femoris: r = 0.52, p < 0.01, vastus lateralis: r = 0.40, p < 0.01) and flexion (semitendinosus: r = 0.41, p < 0.01) torques. After adjusting for the influence of height and/or body mass, the fascia lata thickness showed a partial correlation only with the skeletal muscle thickness at the semitendinosus (r = 0.61, p < 0.01). The present study revealed that the fascia lata has site-specific differences of the thickness, which positively correlates with the underlying muscle thickness and corresponding joint torque. Furthermore, the fascia lata over the semitendinosus is associated with the underlying muscle characteristics independent of the physical constitution. It is assumed that the fascia lata has the plasticity and changes its thickness, which likely corresponds to the morphology of the neighboring tissues and underlying muscle function.

Hamstrings load bearing in different contraction types and intensities: A shear-wave and B-mode ultrasonographic study.

The main aim was to examine the load bearing of individual hamstring muscles in different contraction types and intensities, through local stiffness measurement by shear wave elastography (SWE). A secondary aim was to examine the relationship between the SWE stiffness measure and hamstrings morphology. Ten healthy males (age 22.1±4.1 years; height 173.7±5.9 cm; body mass 68.6±12.4 kg; mean ± SD) performed knee flexions on an isokinetic dynamometer at different intensities (20-70%MVC, random order) in three separate, randomized conditions: isometric (ISO), concentric (CON) and eccentric (ECC). SWE was used to measure muscle shear wave velocity (SWV) in biceps femoris long head (BFlh), semitendinosus (ST) and semimembranosus (SM) during contraction. Muscle anatomical cross-sectional area (ACSA) was measured with magnetic resonance imaging and muscle architecture with B-mode ultrasonography. Muscle SWV increased linearly with contraction intensity, but at a varying rate among muscles and contraction types. ST exhibited greater SWV than BFlh and SM in all contraction types, however, there was an upward shift in the SM SWV-torque relationship in ECC compared to ISO and CON. Strong negative correlations were found between peak ISO SWV and ST ACSA (r = -0.81, p = 0.005) and BFlh pennation angle (r = -0.75, p = 0.012). These results suggest that ST has a primary role in hamstrings load bearing in all contraction types, likely due to its morphology; however, there is evidence of increased contribution from SM in eccentric muscle actions.

Inhomogeneous and Anisotropic Mechanical Properties of the Triceps Surae Aponeuroses in Older Adults: Relationships With Muscle Strength and Walking Performance.

This study investigated (a) site- and direction-dependent variations of passive triceps surae aponeurosis stiffness and (b) the relationships between aponeurosis stiffness and muscle strength and walking performance in older individuals. Seventy-nine healthy older adults participated in this study. Shear wave velocities of the triceps surae aponeuroses at different sites and in two orthogonal directions were obtained in a prone position at rest using supersonic shear imaging. The maximal voluntary isometric contraction torque of the plantar flexors and normal (preferred) and fast (fastest possible) walking speeds (5-m distance) were also measured. The shear wave velocities of the adjoining aponeuroses were weakly associated with plantar flexion torque (r = .23-.34), normal (r = .26), and fast walking speed (r = .25). The results show clear spatial variations and anisotropy of the triceps surae aponeuroses stiffness in vivo, and the aponeurosis stiffness was associated with physical ability in older adults.

Human plantar fascial dimensions and shear wave velocity change in vivo as a function of ankle and metatarsophalangeal joint positions.

The plantar fascia (PF), a primary contributor of the foot arch elasticity, may experience slack, taut, and stretched states depending on the ankle and metatarsophalangeal (MTP) joint positions. Since PF has proximodistal site difference in its dimensions and stiffness, the response to applied tension can also be site specific. Furthermore, PF can contribute to supporting the foot arch while being stretched beyond the slack length, but it has never been quantitatively evaluated in vivo. This study investigated the effects of the ankle and MTP joint positions on PF length and localized thickness and shear wave velocity (SWV) at three different sites from its proximal to distal end using magnetic resonance and supersonic shear imaging techniques. During passive ankle dorsiflexion, rise of SWV, an indication of slack length, was observed at the proximal site when the ankle was positioned by 10°-0° ankle plantar flexion with up to 3 mm (+1.5%) increase in PF length. On the other hand, SWV increased at the distal site when MTP joint dorsiflexed 40° with the ankle 30°-20° plantar flexion, and in this position, PF was lengthened up to 4 mm (+2.3%). Beyond the slack length, SWV curvilinearly increased at all measurement sites toward the maximal dorsiflexion angle whereas PF lengthened up to 9 mm (+7.6%) without measurable changes in its thickness. This study provides evidence that the dimensions and SWV of PF change in a site-specific manner depending on the ankle and MTP joint positions, which can diversify foot arch elasticity during human locomotion.NEW & NOTEWORTHY Joint angle dependence and site specificity of the plantar fascial dimensions and SWV were examined by combining sagittal magnetic resonance and supersonic shear imaging techniques. We revealed that the site-specific changes in PF SWV were related to joint angle positions, i.e., PF slackness and elasticity changed in varying combinations of ankle and MTP angle. Our findings suggest that PF can elastically support the foot arch throughout the stance phase of human bipedal locomotion.

Active Recovery Induces Greater Endurance Adaptations When Performing Sprint Interval Training.

Yamagishi, T and Babraj, J. Active recovery induces greater endurance adaptations when performing sprint interval training. J Strength Cond Res 33(4): 922-930, 2019-This study sought to determine effects of recovery intensity on endurance adaptations during sprint interval training (SIT). Fourteen healthy young adults (male: 9 and female: 5) were allocated to 1 of 2 training groups: active recovery group (ARG, male: 4 and female: 3) or passive recovery group (PRG, male: 5 and female: 2). After having completed a 2-week control period, both groups performed 6 sessions of 4- to 6 30-second sprints interspersed with 4-minute recovery over 2 weeks. However, only ARG cycled at 40% V[Combining Dot Above]O2peak during the 4-minute recovery periods, while PRG rested on the bike or cycled unloaded. After the 2-week training intervention, both groups improved 10-km time-trial performance to a similar extent (ARG: 8.6%, d = 1.60, p = 0.006; PRG: 6.7%, d = 0.96, p = 0.048) without gains in V[Combining Dot Above]O2peak. However, critical power was increased by ARG only (7.9%, d = 1.75, p = 0.015) with a tendency of increased maximal incremental power output (5.3%, d = 0.88, p = 0.063). During the training, active recovery maintained V[Combining Dot Above]O2 and heart rate at a higher level compared with passive recovery (V[Combining Dot Above]O2: p = 0.005, HR: p = 0.018), suggesting greater cardiorespiratory demands with the active recovery. This study demonstrated that greater endurance performance adaptations are induced with active recovery when performing SIT over a short time frame. The findings of the current study indicate that, with active recovery, individuals can gain greater training benefits without increasing total training commitment time. Further studies are required to determine whether differences are seen with recovery intensity over a longer period.

Intracellular-to-total water ratio explains the variability of muscle strength dependence on the size of the lower leg in the elderly.

Bioelectrical impedance spectroscopy (BIS) can assess intracellular water (ICW) and total water (TW) in limbs. This study aimed to examine whether BIS can explain a part of the inter-individual variation of the muscle size-strength relationship in older adults. We analyzed the data of 79 participants aged 64-86 years. The maximal voluntary isometric torques of dorsiflexion and plantar flexion on the right side were measured. The anterior and posterior muscle thickness (MT) in the right lower leg was assessed using ultrasonography. The length of the right lower leg (L) was measured, and the ICW-to-TW ratio (ICW/TW) in the right lower leg was obtained using BIS. The MT was multiplied by L to represent an index of muscle volume (MV). Correlation and stepwise regression analyses were performed. The anterior and posterior MT × L significantly and positively correlated with the muscle torque of dorsiflexion and plantar flexion (r = 0.710 and 0.649, respectively, P < 0.001). In the stepwise regression analyses, ICW/TW was selected as a significant predictor of muscle torque independent of MT × L (P < 0.05) for both dorsiflexion and plantar flexion. Electrical parameters of BIS (membrane capacitance, characteristics frequency, and phase angle) in the lower leg also significantly correlated with muscle torques. In addition, the skeletal muscle mass index (appendicular lean mass/height2) was also associated with ICW/TW (P < 0.001). The present results suggest that ICW/TW explains the interindividual variations of the muscle size-strength relationship.

Riding posture affects quadriceps femoris oxygenation during an incremental cycle exercise in cycle-based athletes.

Although oxygenation levels and muscle recruitment patterns of the quadriceps femoris during an incremental cycling exercise has been reported, oxygenation and activation profiles of the quadriceps femoris in racing posture in cycle-based athletes remain unknown. This study aimed to examine the effects of riding posture on oxygenation and neuromuscular activation of quadriceps femoris during an incremental cycling exercise in cycle-based athletes. Nine cycle-based athletes and nine nonathletic subjects performed an incremental cycling exercise at a constant cadence of 90 rpm. Riding postures were the racing posture using an aero-handle bar (aero posture) and the usual upright racing posture as the control (upright posture). Near-infrared spectroscopy and surface electromyography were recorded from vastus lateralis and rectus femoris. Changes in the tissue oxygenation index of the near-infrared spectroscopy from baseline were calculated, and the amplitudes of electromyographic signals were normalized to the initial values of the exercise in each muscle. In cycle-based athletes, changes in the tissue oxygenation index of vastus lateralis and rectus femoris in the aero posture were significantly lower than those obtained in the upright posture throughout the exercise, whereas no significant differences between the postures were observed in the normalized electromyographic amplitudes of vastus lateralis and rectus femoris. A significant difference between the postures was only occurred in changes of the tissue oxygenation index of rectus femoris in the final phase of exercise in nonathletic subjects. It appears that riding posture affects the oxygenation pattern of quadriceps femoris during incremental cycling exercise in cycle-based athletes. The main results of this study suggest that aero posture during incremental cycle exercise enhanced the muscular oxygen consumption of the quadriceps femoris in the trained cyclists.

Influence of recovery intensity on oxygen demand and repeated sprint performance.

BACKGROUND: This study aimed to determine effects of recovery intensity (passive, 20%, 30% and 40% V̇O2peak) on oxygen uptake kinetics, performance and blood lactate accumulation during repeated sprints. METHODS: Seven moderately-trained male participants (V̇O2peak: 48.1±5.1 mL/kg/min) performed four 30-second repeated Wingate tests on four separate occasions. RESULTS: Recovery of V̇O2 between sprints was prolonged with recovery intensity (time required to reach 50% V̇O2peak: passive: 50±9 s; 20%: 81±17 s; 30%: 130±43 s; 40%: 188±62 s, P<0.001), while V̇O2-to-sprint work ratio was mainly increased by the higher intensities (passive: 138±17 mL/min/kJ; 20%: 149±14 mL/min/kJ; 30%: 159±15 mL/min/kJ; 40%: 158±17 mL/min/kJ, P=0.001). The decline in peak power tended to be greater in the higher intensity conditions during sprint 2 (passive: 7.4±5.4%; 20%: 5.8±7.9%; 30%: 12.7±7.4%; 40%: 12.7±5.5%, P=0.052), whereas average power was less decreased with recovery intensity during sprint 4 (passive: 22.4±8.9%; 20%: 19.9±6.1%; 30%: 18.4±7.3%; 40%: 16.6±6.2%, P=0.036). Blood lactate was not different with recovery intensity (P=0.251). CONCLUSIONS: The present study demonstrated that while the higher recovery intensities induce prolonged oxygen recovery and impaired peak power restoration during the initial sprints, those intensities provide a greater aerobic contribution to sprint performance, resulting in better power maintenance during the latter sprints.