Short-Term Hypoxic Exposure and Training Improve Maximal Anaerobic Running Test Performance.

Oriishi, M, Matsubayashi, T, Kawahara, T, and Suzuki, Y. Short-term hypoxic exposure and training improve maximal anaerobic running test performance. J Strength Cond Res 32(1): 181-188, 2018-The purpose of this study was to examine the effectiveness of short-term hypoxic exposure and training in the performance of competitive 400- or 800-m runners. Fifteen female competitive 400- and 800-m runners volunteered to participate and were assigned to either the hypoxic (n = 7) or normoxic (n = 8) group. The subjects completed 6 days of training. The hypoxic group trained and slept in normobaric hypoxia, with oxygen concentrations of 14.4 and 16.5% for training and sleep, respectively. The normoxic group trained and slept at sea level. The subjects completed 4 sprint and 5 endurance training sessions during the camp. The subjects underwent a maximal anaerobic running test before and 8 days after the training camp. The maximal power determined by the anaerobic running test improved significantly in the hypoxic group (p ≤ 0.05). Blood lactate concentration at submaximal running speed (275, 300, and 375 m·min) in the hypoxic group decreased significantly (p ≤ 0.05) after the training period. No significant changes in these values were found in the normoxic group. These results suggest that 6 days of hypoxic exposure and training enhanced performance and improved lactate metabolism in 400- and 800-m runners.

Possibility of intrinsic muscle contractile properties in force summation and postactivation potentiation as indices of maximal muscle strength and muscle fatigue.

INTRODUCTION: We investigated whether intrinsic muscle contractile properties in force summation and postactivation potentiation (PAP) can be used as indices of maximal muscle strength and muscle fatigue. METHODS: Twelve men participated in this study. The maximum voluntary contraction torque (MVC), torque evoked by several stimulations in the tibialis anterior (TA) muscle, force summation parameters, and PAP were evaluated with the progression of fatigue. The force summation parameters were evaluated with respect to responses of single, double, and triple stimulations. RESULTS: The percent decreases in the evoked torque parameters with or without PAP were greater than those during MVC. Force summation parameters were significantly related to MVC and fatigue resistance. CONCLUSIONS: Intrinsic muscle contractile properties with or without PAP in the TA overestimate fatigue during MVC. However, force summation parameters can be used as indices of maximal muscle strength with or without fatigue and fatigue resistance capacity.

Relationship between bilateral differences in single-leg jumps and asymmetry in isokinetic knee strength.

The aims of the study were to investigate the differences in kinematics and kinetics between the dominant and nondominant leg during single-leg jumps without arm swing, and to determine the relationship between bilateral asymmetry in isokinetic knee strength and the single-leg jump. Isokinetic knee strength and single-leg jump kinematics and kinetics were measured in 11 male participants. The bilateral asymmetry index was calculated for each parameter. For isokinetic knee strength, there were no significant differences between the dominant and nondominant legs. Significant correlations were observed for the bilateral asymmetry index for isokinetic knee strength at 180 degrees per second and the bilateral asymmetry indexes for maximum flexion angle and the mean knee joint torque during the single-leg jumps. In conclusion, the findings of the current study suggest an association between knee strength imbalances and the joint angle, as well as the torque produced in single-leg jumps, although no relationship between knee strength and jump height was observed.

Comparison of the snatch technique for female weightlifters at the 2008 Asian championships.

The purpose of this study was to compare the snatch techniques of Japanese and international female weightlifters. Two high-speed cameras operating at 250 Hz were used to record the snatch lifts of the 5 best weightlifters in the snatch and 5 Japanese weightlifters during the 2008 Asian Weightlifting Championships held in Japan. The results revealed that the forward velocity of the barbell for the Japanese weightlifters during the second pull was significantly greater than that for the best weightlifters and that barbell trajectories of Japanese weightlifters except for the 53-kg class crossed the vertical reference line with great forward displacement of the barbell. In addition, the best weightlifters extended the knee and hip joints during the second pull earlier than the Japanese weightlifters did. These findings indicate that it is important to improve the way of pulling the barbell during the second pull for Japanese female weightlifters.

Bilateral asymmetry in joint torque during squat exercise performed by long jumpers.

This study aimed to examine the bilateral differences in movement and joint torques during the squat exercise by using kinematic and kinetic analyses. Eighteen long jumpers participated in this study. They performed 3 repetitions of the squat exercise with loads of 50, 70, and 90% of their 3 repetition maximum (3RM). During the exercise, their movement was recorded using a Vicon motion capture system. Ground reaction forces (GRFs) were simultaneously measured by 2 force platforms, one under each foot. On the basis of these position and force data, joint angles and torques for the hip, knee, and ankle were calculated using inverse dynamics. Results showed that the peak vertical and horizontal GRFs did not differ between the takeoff and non-takeoff legs in any loading condition. However, the maximal flexion angle and peak torque at hip showed significant differences between the limbs under all loading conditions (p < 0.05). In addition, the peak ankle torque in the takeoff leg was larger than that in the non-takeoff leg under a load of 90% of 3RM. These results indicate that joint torques may be bilaterally asymmetric when long jumpers perform the squat exercise, which should be considered when attempting to decrease the risk of injury.

Short-Term Intermittent Hypoxic Resistance Training Does Not Impair Osteogenic Response in Sea Level Residents.

Background: Osteogenic responses induced by training under hypoxia remain unclear. We aimed to investigate whether intermittent hypoxic resistance training affects osteogenic responses. Materials and Methods: Sixteen male participants underwent resistance training under normoxia (NRT; n = 7) or hypoxia (HRT; O2 = 14.4%, n = 9), twice a week for 8 weeks. The HRT group exercised and rested for 30 minutes under hypoxia, with total hypoxic exposure time in one session of ∼60 minutes. At pre- and postexperiment, bone mineral density (BMD) of the whole body and right proximal femur was measured. At the first and last training sessions, bone alkaline phosphatase (BAP), osteocalcin (OC), cross-linked N-telopeptide of type I collagen (NTx), type I collagen cross-linked C-telopeptide (ICTP), interleukin-6 (IL-6), and blood lactate (La) concentration were analyzed at rest and postexercise. Results: BMD did not change with training and hypoxia. Although BAP, OC, and ICTP levels at rest significantly increased with training (p < 0.01, 0.05, and 0.05, respectively), they did not change with hypoxia. NTx and IL-6 did not change. Additionally, changing patterns of bone markers and La induced by a single bout of exercise were similar among groups in both training sessions. Conclusions: Short-term resistance training enhanced overall bone metabolism, regardless of the oxygen level. Hypoxia has no effects on osteogenic responses.

Kinematics of the thorax and pelvis during accelerated sprinting.

BACKGROUND: This study aimed to describe changes in thoracic and pelvic movements during the acceleration phase of maximal sprinting, and to clarify which kinematic variable relates to better accelerated sprinting performance. METHODS: Twelve male sprinters performed 60-m sprints, during which three-dimensional step-to-step changes in thoracic and pelvic angles, as well as the trunk quasi-joint angle, were obtained throughout a 50-m distance. RESULTS: The patterns of thoracic and pelvic movements were maintained throughout the entire acceleration phase, although the phase profiles of the relative movements between the thorax and pelvis in three planes differed. Increase in peak thoracic and pelvic tilt angles terminated (-10.3° and 3.2° from the vertical line) and trunk extension range (≈21.7°) decreased from the 13th-15th steps. Moreover, thoracic and pelvic obliquity angles decreased from 15.3° and 8.8°, and conversely, rotation angles increased to 23.5° and plateaued (≈16°), during the entire acceleration phase. Moreover, smaller inclination of the thorax and deeper inclination of the pelvis, smaller rotations of the pelvis and trunk quasi-joint and greater thoracic obliquity during the initial section (to the 4th step), deeper inclination of the pelvis during the middle section (to the 14th step), and smaller trunk torsion and thoracic obliquity during the final section in the entire acceleration phase of sprinting were associated with increases in running speed. CONCLUSIONS: The results suggest that sprint acceleration toward maximal speed is not performed with only proportional increases in magnitudes of trunk movements, and important factors for better sprint acceleration performance alter with increasing running speed.

Alteration of swing leg work and power during human accelerated sprinting.

This study investigated changes in lower-extremity joint work and power during the swing phase in a maximal accelerated sprinting. Twelve male sprinters performed 60 m maximal sprints while motion data was recorded. Lower-extremity joint work and power during the swing phase of each stride for both legs were calculated. Positive hip and negative knee work (≈4.3 and ≈-2.9 J kg-1) and mean power (≈13.4 and ≈-8.7 W kg-1) during the entire swing phase stabilized or decreased after the 26.2±1.1 (9.69±0.25 m s-1) or 34.3±1.5 m mark (9.97±0.26 m s-1) during the acceleration phase. In contrast, the hip negative work and mean power during the early swing phase (≈7-fold and ≈3.7-fold increase in total), as well as the knee negative work and power during the terminal swing phase (≈1.85-fold and ≈2-fold increase in total), increased until maximal speed. Moreover, only the magnitudes of increases in negative work and mean power at hip and knee joints during the swing phase were positively associated with the increment of running speed from the middle of acceleration phase. These findings indicate that the roles of energy generation and absorption at the hip and knee joints shift around the middle of the acceleration phase as energy generation and absorption at the hip during the late swing phase and at the knee during early swing phase are generally maintained or decreased, and negative work and power at hip during the early swing phase and at knee during the terminal swing phase may be responsible for increasing running speed when approaching maximal speed.

Kinematics of transition during human accelerated sprinting.

This study investigated kinematics of human accelerated sprinting through 50 m and examined whether there is transition and changes in acceleration strategies during the entire acceleration phase. Twelve male sprinters performed a 60-m sprint, during which step-to-step kinematics were captured using 60 infrared cameras. To detect the transition during the acceleration phase, the mean height of the whole-body centre of gravity (CG) during the support phase was adopted as a measure. Detection methods found two transitions during the entire acceleration phase of maximal sprinting, and the acceleration phase could thus be divided into initial, middle, and final sections. Discriminable kinematic changes were found when the sprinters crossed the detected first transition-the foot contacting the ground in front of the CG, the knee-joint starting to flex during the support phase, terminating an increase in step frequency-and second transition-the termination of changes in body postures and the start of a slight decrease in the intensity of hip-joint movements, thus validating the employed methods. In each acceleration section, different contributions of lower-extremity segments to increase in the CG forward velocity-thigh and shank for the initial section, thigh, shank, and foot for the middle section, shank and foot for the final section-were verified, establishing different acceleration strategies during the entire acceleration phase. In conclusion, there are presumably two transitions during human maximal accelerated sprinting that divide the entire acceleration phase into three sections, and different acceleration strategies represented by the contributions of the segments for running speed are employed.

Effects of systemic hypoxia on human muscular adaptations to resistance exercise training.

Hypoxia is an important modulator of endurance exercise-induced oxidative adaptations in skeletal muscle. However, whether hypoxia affects resistance exercise-induced muscle adaptations remains unknown. Here, we determined the effect of resistance exercise training under systemic hypoxia on muscular adaptations known to occur following both resistance and endurance exercise training, including muscle cross-sectional area (CSA), one-repetition maximum (1RM), muscular endurance, and makers of mitochondrial biogenesis and angiogenesis, such as peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), citrate synthase (CS) activity, nitric oxide synthase (NOS), vascular endothelial growth factor (VEGF), hypoxia-inducible factor-1 (HIF-1), and capillary-to-fiber ratio. Sixteen healthy male subjects were randomly assigned to either a normoxic resistance training group (NRT, n = 7) or a hypoxic (14.4% oxygen) resistance training group (HRT, n = 9) and performed 8 weeks of resistance training. Blood and muscle biopsy samples were obtained before and after training. After training muscle CSA of the femoral region, 1RM for bench-press and leg-press, muscular endurance, and skeletal muscle VEGF protein levels significantly increased in both groups. The increase in muscular endurance was significantly higher in the HRT group. Plasma VEGF concentration and skeletal muscle capillary-to-fiber ratio were significantly higher in the HRT group than the NRT group following training. Our results suggest that, in addition to increases in muscle size and strength, HRT may also lead to increased muscular endurance and the promotion of angiogenesis in skeletal muscle.

Fatigue-induced changes in longitudinal relaxation time determined by magnetic resonance imaging.

Longitudinal relaxation time (T(1)) determined by 3.0-T magnetic resonance imaging of the tibialis anterior and extensor digitorum longus muscles increased gradually with muscle fatigue caused by three 120-s periods of repeated ankle dorsiflexion separated by 5-min rest periods. T(1) values decreased in the recovery period, although they remained higher than the preexercise values. T(1) values for the soleus muscle were unchanged throughout the experiment. Results suggest that muscle T(1) values increase with increasing muscle fatigue.

Ultrasonographic measurement of tendon displacement caused by active force generation in the psoas major muscle.

The purpose of this study was to examine the validity of using ultrasonography for detecting the force generated by the psoas major muscle, a muscle positioned in the deep trunk. We measured the displacement of central tendon on B-mode ultrasound images of two different longitudinal sections of the muscle during passive hip flexion-extension and isometric hip flexion at varied hip angles. In both tasks, the values of tendon displacement obtained independently from each section coincided well, indicating that tendon displacement took place along a straight trajectory, i.e., close to the nodal line between two scanned planes. It was strongly correlated with both the hip angle (R(2) = 0.98) and the hip-flexion torque (R(2) = 0.83). In the second set of experiment, we measured the tendon displacement during dynamic movements with the combination of ultrasonography and VICON-based motion analysis. From the tendon displacement during dynamic thigh lifting and walking, the force generated by the muscle could be estimated by extracting the force-related component. These results indicate that ultrasonography of the psoas major muscle can measure the displacement of its central tendon accompanied with either length change of the muscle or the elongation of tendon. Although much attention has to be paid to the limitations of this methodology, ultrasonography may be useful for detecting the force generation of the muscle during a variety of dynamic movements.