Home-based resistance training performed at either fast or slow speeds improves power output in older adults.

PURPOSE: We investigated the effect of an unsupervised, body mass- home-based resistance training program in older adults performed at either a fast or slow contractile speed on changes to muscle-power, -volume, -architecture, and fatigue resistance of the knee extensors. METHODS: Thirty-two male older adults (age 65-88 years) were separated into 1) fast-speed exercise (Fast-group), 2) slow-speed exercise (Slow-group), and 3) no exercise (Control-group) groups. Participants in the exercise groups performed 30-45 repetitions of knee-extension and sit-to-stand exercises 3 times a week for 8 weeks with different exercise speed between the groups. Before and after the intervention period, the following variables were measured: Isotonic power, isometric strength, twitch contractile properties, muscle-activity, -architecture, and -quality, neuromuscular fatigue resistance of the knee extensors, and thigh muscle volume. RESULTS: Peak power was increased in both the Fast-group (+24 %, P < 0.01, d = 0.65) and Slow-group (+12 %, P < 0.05, d = 0.33) but not in the Control-group. Training increased pennation angle of the vastus lateralis in both the Fast-group (+8 %, P < 0.01, d = 0.42) and Slow-group (+8 %, P < 0.01, d = 0.42), while only the Fast-group showed increase in pennation angle of the rectus femoris (+12 %, P < 0.01, d = 0.64) and thigh muscle volume (+16 %, P < 0.01, d = 0.52). There was no time × group interaction effect for the other neuromuscular measures. CONCLUSIONS: Unsupervised, body mass- and home-based resistance training performed at either fast or slow speeds can improve muscle power in older adults, while fast-speed exercise may be preferable over slow-speed owing to the relatively greater improvement of muscle-power, -volume, -architecture, and better time efficiency.

Black Soybean Seed Coat Extract Improves Endothelial Function and Upregulates Oxidative Stress Marker Expression in Healthy Volunteers by Stimulating Nitric Oxide Production in Endothelial Cells.

Black soybean seed coat extract (BE) contains multiple bioactive polyphenols, including flavan-3-ols and anthocyanins. BE improves endothelial function; however, it is unclear whether BE protects endothelial cells from senescence. In this study, we examined the effects of BE on endothelial cell senescence and vascular function in healthy individuals. High concentrations of glucose were used to induce senescence in bovine aortic endothelial cells incubated with BE. Senescence, vascular function, and oxidative stress markers were measured. Incubation with BE remarkably inhibited senescence-associated ß-galactosidase and lactate dehydrogenase activities and dose dependently reduced intracellular reactive oxygen species levels in bovine aortic endothelial cells. BE treatment increased the levels of endothelial nitric oxide synthase (eNOS) mRNA and endothelial nitric oxide (NO) metabolites and increased the mRNA expression of klotho, a gene associated with an antiaging phenotype. To examine the effects of BE in humans, we conducted a clinical study using the second derivative of the fingertip photoplethysmogram to investigate vascular function and aging in 24 healthy volunteers. The participants consumed BE supplements (100 mg/day) or a placebo for 2 weeks. When compared with the placebo group, the BE group showed considerably improved vascular function, NO metabolite levels, and oxidative stress. These results suggest that BE supplementation improves endothelial function, possibly through antioxidant activity and NO production, and may consequently reduce the cardiovascular risk associated with aging. BE supplementation may be an effective and safe approach to reduce the risk of atherosclerosis and cardiovascular disease; however, additional studies investigating chronic vascular inflammation are needed.

A Rare Case of Drug Reaction with Eosinophilia and Systemic Symptoms Syndrome Leading to Hemodialysis and Multiple Infections: A Case Report and Literature Review.

Drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome is a severe drug eruption that causes multiple organ damage. The renal impairment in these patients usually improves with immunosuppressants, but subsequent infections often develop. We herein report a rare case of DRESS syndrome leading to hemodialysis and multiple infections with Pneumocystis pneumonia, cytomegalovirus and Aspergillus despite the administration of low-dose prednisolone. We also present a literature review of cases requiring dialysis after DRESS syndrome. In patients with chronic kidney disease, it is important to be alert for not only the development of DRESS syndrome but also subsequent infections.

Acute effect of static stretching on non-muscular tissue stiffness and joint flexibility: a comparative study between older and young men.

PURPOSE: Non-muscular tissue stiffness is assumed to have a negative impact on joint flexibility, and a reduction in non-muscular tissue stiffness may be important, especially in older adults. The present study aimed to compare the acute effects of static stretching on non-muscular tissue stiffness between older and young adults and to investigate whether a decrease in tissue stiffness improves joint flexibility. METHODS: Twenty older (62-83 years) and 20 young (21-24 years) males participated. Ankle dorsiflexion static stretching (five sets of 90 s each) was performed, and before and after stretching, the ankle dorsiflexion range of motion (RoM), passive ankle joint stiffness, and shear wave speed (SWS) (an index of stiffness) of the sciatic nerve, tibial nerve, and posterior thigh fascia were measured. RESULTS: Stretching led to an increase in RoM and a decrease in passive joint stiffness in both groups (P < 0.001) with no significant between-group differences (P ≥ 0.055). The between-group difference in the effect of stretching on SWS was evident only for the sciatic nerve, and a decline in sciatic nerve SWS was only observed in the older adult group (pre-stretching: 2.5 ± 0.3 m/s; post-stretching: 2.3 ± 0.4 m/s; P = 0.027). A significant positive repeated-measures correlation was observed between the sciatic nerve SWS and passive joint stiffness (P = 0.014, rrm = 0.540). CONCLUSION: The reduction in sciatic nerve stiffness by stretching was noticeable in older men and led to improved joint flexibility. These findings may provide insight into tissue adaptation by stretching and may be used to explore effective exercises for improving joint flexibility in older adults.

Relation of leg phase angle from bioelectrical impedance analysis with voluntary and evoked contractile properties of the plantar flexors.

Introduction: Bioelectrical impedance analysis (BIA) can noninvasively and quickly assess electrical properties of the body, such as the phase angle. Phase angle is regarded as the quantity and/or quality of skeletal muscle and is associated with exercise performance, such as jump height and walking speed. Although the phase angle derived from BIA is assumed to be a useful way to assess muscle function, the relationship between the phase angle and neuromuscular properties has not been fully investigated. The purpose of this study was to investigate the association of phase angle with voluntary and evoked contractile properties in 60 adults (age, 21-83 years; 30 females and 30 males). Methods: The phase angle of the right leg at 50 kHz was evaluated using BIA. The twitch contractile properties (peak twitch torque [PTtwitch], rate of twitch torque development [RTDtwitch], and time-to-PTtwitch [TPTtwitch]) of the plantar flexors were measured using tibial nerve electrical stimulation. Maximal voluntary isometric contractions (MVICs) were performed to measure the maximal muscle strength and explosive muscle strength, from which the peak MVIC torque (PTMVIC) and rate of torque development (RTD) over a time interval of 0-200 ms were assessed, respectively. The root mean square (RMS) values of electromyographic (EMG) activity during the PTMVIC and RTD measurements (EMG-RMSMVIC and EMG-RMSRTD, respectively) were calculated. The RTD and EMG-RMSRTD were normalized using PTMVIC and EMG-RMSMVIC, respectively. Results and discussion: Phase angle significantly correlated with twitch contractile properties (|r| ≥ 0.444, p < 0.001), PTMVIC (r = 0.532, p < 0.001), and RTD (r = 0.514, p < 0.001), but not with normalized RTD (r = 0.242, p = 0.065) or normalized EMG-RMSRTD (r = -0.055, p = 0.676). When comparing measurement variables between the low- and high-phase angle groups while controlling for sex and age effects, the high-phase angle group showed greater PTtwitch, RTDtwitch, PTMVIC, and RTD (p < 0.001) and shorter TPTtwitch (p < 0.001) but not normalized RTD (p = 0.184) or normalized EMG-RMSRTD (p = 0.317). These results suggest that the leg phase angle can be an indicator of voluntary and evoked muscle contractile properties but not the neuromuscular activity of the plantar flexors, irrespective of sex and age.

Cinnamtannin A2, (-)-epicatechin tetramer, attenuates skeletal muscle wasting in disuse atrophy model mice induced by hindlimb suspension.

The impact of repeated administration of cinntamtannin A2 (A2, 25 µg/kg) on skeletal muscle disuse atrophy model mice induced by hindlimb suspension for 14 days was examined. In soleus, weight loss and a reduction in the average myofibre size with shifting to the smaller side of the peak were observed in the suspension-vehicle group, but A2 reduced these changes. Average myofibre size significantly increased in ground-A2 compared to ground-vehicle. A marked increase in the dephosphorylation of forkhead box O (FoxO) 3a by the suspension was reduced by A2. The phosphorylation of protein kinase B (Akt) and eukaryotic translation initiation factor 4E-binding protein (4EBP)-1 were significantly increased by the treatment of A2. In addition, a single dose of A2 increased dramatically in the 24-h excretion of catecholamines in urine. These results suggest that A2 administration results in sympathetic nerve activation and promotes hypertrophy while inhibiting the progress of disuse muscle atrophy.

A report of three cases of patients with tubulointerstitial nephritis with IgM-positive plasma cells, treatment, and serum-IgM as a sensitive marker for relapse.

BACKGROUND: Tubulointerstitial nephritis with IgM-positive plasma cells (IgMPC-TIN) is a newer disease about which there are many unclear points. Glucocorticoid therapy is effective in many cases of IgMPC-TIN; however, relapse during glucocorticoid tapering has been reported. Relapse and its treatment are poorly defined. CASE PRESENTATION: Case 1 was a 61-year-old man with renal dysfunction and proteinuria. Tubulointerstitial nephritis and IgM-positive plasma cells were observed in a renal biopsy. He was diagnosed with IgMPC-TIN accompanied by Fanconi syndrome and distal renal tubular acidosis (d-RTA). Prednisolone (PSL; 30 mg daily, 0.45 mg/kg/day) treatment was highly effective, and PSL was gradually tapered and discontinued after 1 year. However, 1 month after PSL discontinuation, therapeutic markers were elevated. Therefore, PSL (10 mg daily, 0.15 mg/kg/day) was administered, and the markers indicated improvement. Case 2 was a 43-year-old woman referred for renal dysfunction and proteinuria. Laboratory data revealed that she had primary biliary cholangitis (PBC), d-RTA, and Fanconi syndrome. A renal biopsy showed accumulation of IgM-positive plasma cells in the tubulointerstitium without any glomerular changes. A diagnosis of IgMPC-TIN was made and the patient was started on PSL (35 mg daily, 0.6 mg/kg/day). Therapeutic markers decreased immediately and PSL was discontinued after 1 year. Three months later, the proteinuria and Fanconi syndrome worsened. PSL treatment was restarted (20 mg daily, 0.35 mg/kg/day) and markers indicated improvement. Case 3 was a 45-year-old woman with renal dysfunction and proteinuria. Tubulointerstitial nephritis and IgM-positive plasma cells were observed in a renal biopsy. The patient had PBC, Sjögren syndrome, d-RTA, and Fanconi syndrome, and the diagnosis of IgMPC-TIN was made. The patient was started on PSL (30 mg daily, 0.4 mg/kg/day) and disease markers decreased immediately. However, when PSL was tapered to 15 mg daily (0.2 mg/kg/day), the patient's serum IgM levels increased; therefore, we maintained the PSL at 15 mg daily (0.2 mg/kg/day). CONCLUSION: We report three cases of relapsed IgMPC-TIN associated with reduction or discontinuation of glucocorticoid therapy. In these cases, elevation of serum IgM preceded that of other markers such as urinary ß2-microglobulin, proteinuria, and glycosuria. We recommend monitoring serum IgM levels while tapering glucocorticoids; a maintenance dose of glucocorticoid should be considered if relapse is suspected or anticipated.

Eight-week neuromuscular electrical stimulation training produces muscle strength gains and hypertrophy, and partial muscle quality improvement in the knee extensors.

This study investigated the effect of an 8-week neuromuscular electrical stimulation (NMES) training programme (3 days/week) on muscle quantity and quality and single-joint performance in the knee extensors. Thirty-nine untrained young male participants were randomly assigned to NMES training (n = 21) and control (n = 18) groups. The 8-week NMES training induced significant increase in the isometric maximal voluntary contraction (MVC) torque of the knee extensors (≈9.3%), muscle volume of the individual and entire quadriceps muscles determined by magnetic resonance imaging (≈3.3%-6.4%), and a significant decrease in the ultrasound echo intensity of the vastus lateralis (≈-4.0%); however, hypertrophy of the vastus intermedius (i.e., the deep muscle) was limited (≈3.3%). In the NMES training group, the repeated measures correlations of the isometric MVC torque with the muscle volume of the entire quadriceps muscle and each quadriceps muscle were significant (rrm (20) = 0.551-0.776), whereas that of the isometric MVC torque with the ultrasound echo intensity of the vastus lateralis was not significant. These findings suggest that NMES training produces muscle strength gains, muscle hypertrophy, and partial muscle quality improvement and that the NMES training-induced muscle strength gains is caused by muscle hypertrophy in the knee extensors.

Effects of three-dimension movie visual fatigue on cognitive performance and brain activity.

To further develop three-dimensional (3D) applications, it is important to elucidate the negative effects of 3D applications on the human body and mind. Thus, this study investigated differences in the effects of visual fatigue on cognition and brain activity using visual and auditory tasks induced by watching a 1-h movie in two dimensions (2D) and 3D. Eighteen young men participated in this study. Two conditions were randomly performed for each participant on different days, namely, watching the 1-h movie on television in 2D (control condition) and 3D (3D condition). Before and after watching the 1-h movie on television, critical flicker fusion frequency (CFF: an index of visual fatigue), and response accuracy and reaction time for the cognitive tasks were determined. Brain activity during the cognitive tasks was evaluated using a multi-channel near-infrared spectroscopy system. In contrast to the control condition, the decreased CFF, and the lengthened reaction time and the decreased activity around the right primary somatosensory cortex during Go/NoGo blocks in the visual task at post-viewing in the 3D condition were significant, with significant repeated measures correlations among them. Meanwhile, in the auditory task, the changes in cognitive performance and brain activity during the Go/NoGo blocks were not significant in the 3D condition. These results suggest that the failure or delay in the transmission of visual information to the primary somatosensory cortex due to visual fatigue induced by watching a 3D movie reduced the brain activity around the primary somatosensory cortex, resulting in poor cognitive performance for the visual task. This suggests that performing tasks that require visual information, such as running in the dark or driving a car, immediately after using a 3D application, may create unexpected risks in our lives. Thus, the findings of this study will help outlining precautions for the use of 3D applications.

Association between interindividual variability in training volume and strength gain.

This study aimed to examine the association between interindividual variability in strength changes and in training volume. A total of 26 untrained men completed 4-weeks of isometric knee extension (KE group, n = 12) and hip flexion (HF group, n = 14) training. Each training session comprised four sets of ten isometric contractions, 3-s contractions every 20 s. Training volume, which was defined as impulse during contractions, and maximal voluntary contraction (MVC) torque during KE and HF were evaluated. Based on the magnitude of MVC torque changes, the participants were divided into the high and low responders (n = 13; KE = 6 and HF = 7 per responders). The MVC torque changes (KE, 20.8%; HF, 22.4%) and total training volume did not significantly differ between the two groups. A higher training volume was demonstrated in the low responders than the high responders. The total training volume was positively associated with the MVC torque changes in low responders (r = 0.869%, 95% confidence interval [0.610, 0.960], p < 0.001), but not in high responders [r = 0.229, 95% confidence interval (-0.368, 0.693), p = 0.451], KE or HF group. Results showed that training volume was an important factor in determining the magnitude of strength gains in low responders, and MVC torque could improve by approximately 20% with the use of the study protocol regardless of joint actions involved during training.

Membrane capacitance and characteristic frequency are associated with contractile properties of skeletal muscle.

The cell membrane capacitance (Cm) and characteristic frequencies (fc) of tissues can be obtained using segmental bioelectrical impedance spectroscopy (S-BIS). Higher Cm and lower fc are associated with a larger surface area of skeletal muscle fibers with T-tubules in the tissues. Muscle fiber membrane is one of the major physiological factors that influence surface electromyograms (EMGs) as well as the number of recruited motor units so that the amplitude of surface EMG may be correlated with Cm and fc. The aim of the current study was to examine the association of fc or Cm in the lower leg with contractile and neuromuscular properties in the plantar flexors. We analyzed data from 59 participants (29 women) aged 21-83 years. The Cm, fc, and intracellular water (ICW) in the lower leg were obtained using S-BIS. We measured electrical-evoked torque, maximal voluntary contraction (MVC) torque, and amplitude of EMG normalized by the M wave during MVC contraction. The high Cm group had a significantly lower fc and significantly higher MVC torque, estimated maximum torque, twitch torque, and root mean square (RMS) of EMG normalized by the M wave (EMG:M) in the musculus triceps surae compared to the low Cm group (P < 0.05). Cm was positively and fc was negatively correlated with the nRMS of EMG:M in the triceps surae (P < 0.05). S-BIS recordings can be used to detect changes in skeletal muscle membrane capacitance, which may provide insights into the number of T-tubules. The muscle capacitance measured with S-BIS can be predictive of muscle force generation.

Can phase angle from bioelectrical impedance analysis associate with neuromuscular properties of the knee extensors?

Maintenance and improvement of neuromuscular functions is crucial for everyone regardless of age. An easy way to assess neuromuscular properties without muscle contraction is useful especially for those who cannot perform strenuous muscular force production, such as older adults and patients with orthopedic or cognitive disorders. Bioelectrical impedance analysis (BIA) can assess body electrical properties e.g., phase angle (PhA) which is regarded as muscle quantity/quality index. The purpose of this study was to investigate associations of PhA with neuromuscular properties of the knee extensors in 55 young (n = 23) and older (n = 32) adults. The values of PhA of the right thigh and whole-body were determined with BIA at 50 kHz. The participants performed 4-s maximal voluntary isometric contraction (MVIC) to measure peak torque (PTMVIC), and 1-s brief MVIC to assess rate of torque development (RTD) over the time interval of 0-200 ms. As markers of physiological mechanisms of muscle force production, twitch contractile properties (peak twitch torque, rate of twitch torque development, and time-to-peak twitch torque) of the knee extensors obtained by femoral nerve electrical stimulation, and muscle activity assessed as root mean square values of electromyographic activity (EMG-RMS) during PTMVIC and RTD measurements were measured. Thigh and whole-body PhA significantly correlated with PTMVIC (r ≥ 0.555, p < 0.001) and electrically evoked twitch parameters (peak twitch torque, rate of twitch torque development, and time-to-peak twitch torque; |r| ≥ 0.420, p ≤ 0.001), but not RTD (r ≤ 0.237, p ≥ 0.081) or EMG-RMSs (|r| ≤ 0.214, p ≥ 0.117). Stepwise multiple linear regression analysis revealed that thigh PhA was selected as a significant variable to predict PTMVIC but not RTD. Whole-body PhA was not selected as a significant variable to predict PTMVIC or RTD. In conclusion, both thigh and whole-body PhA can associate with maximal voluntary muscle strength of the knee extensors, and this association may be due to intrinsic contractile properties but not neural aspects. Regarding prediction of the knee extensor strength, thigh PhA is preferable as the predictor rather than whole-body PhA which is used as a widely acknowledged indicator of sarcopenia.

Muscle quality indices separately associate with joint-level power-related measures of the knee extensors in older males.

PURPOSE: The purpose of this study was to investigate associations of muscle quality indices with joint-level power-related measures in the knee extensors of thirty-two older males (65-88 years). METHODS: Muscle quality indices included: echo intensity, ratio of intracellular- to total water content (ICW/TW), and specific muscle strength. Echo intensity was acquired from the rectus femoris (EIRF) and vastus lateralis (EIVL) by ultrasonography. ICW/TW was computed from electrical resistance of the right thigh obtained by bioelectrical impedance spectroscopy. Specific muscle strength was determined as the normalized maximal voluntary isometric knee extension (MVIC) torque to estimated knee extensor volume. Isotonic maximal effort knee extensions with a load set to 20% MVIC torque were performed to obtain the knee extension power-related measures (peak power, rate of power development [RPD], and rate of velocity development [RVD]). Power and RPD were normalized to MVIC. RESULTS: There were no significant correlations between muscle quality indices except between EIRF and EIVL (|r|≤ 0.253, P ≥ 0.162). EIRF was negatively correlated with normalized RPD and RVD (r ≤ - 0.361, P ≤ 0.050). ICW/TW was positively correlated with normalized peak power (r = 0.421, P = 0.020). Specific muscle strength was positively correlated with absolute peak power and RPD (r ≥ 0.452, P ≤ 0.012). CONCLUSION: Knee extension power-related measures were lower in participants with higher EI, lower ICW/TW, and lower specific muscle strength, but the muscle quality indices may be determined by independent physiological characteristics.

Can a Short-term Daily Oral Administration of Propolis Improve Muscle Fatigue and Recovery?

This study investigated the effect of 1-week oral administration of propolis on muscle fatigue and recovery after performing a fatigue task (total 100 maximal voluntary concentric knee extension repetitions). In this placebo-controlled, double-blind study, 18 young men consumed a formulation with high Brazilian green propolis dose (H-BGP), a formulation with low Brazilian green propolis dose, or a placebo, for 1 week before performing the fatigue task (an interval between each intervention: 1-2 weeks). Maximal voluntary contraction torque, central fatigue (voluntary activation and root mean square values of the surface electromyography amplitude), and peripheral fatigue (potentiated triplet torque) were assessed before, immediately after, and 2 minutes after the fatigue task. Maximal voluntary contraction torque decreased immediately after the fatigue task in all conditions (P<0.001); however, it recovered from immediately after to 2 minutes after the fatigue task only in the H-BGP condition (P<0.001). Furthermore, there was a significant decrease in voluntary activation (P<0.001) and root mean square values of the surface electromyography amplitude (P≤0.035) only in the placebo condition. No significant difference was observed in the time-course change in potentiated triplet torque between the conditions. These results suggest that oral administration of propolis promotes muscle fatigue recovery by reducing central fatigue.

Trade-Off Between Maximal Power Output and Fatigue Resistance of the Knee Extensors for Older Men.

This study investigated associations of fatigue resistance determined by an exercise-induced decrease in neuromuscular power with prefatigue neuromuscular strength and power of the knee extensors in 31 older men (65-88 years). A fatigue task consisted of 50 consecutive maximal effort isotonic knee extensions (resistance: 20% of prefatigue isometric maximal voluntary contraction torque) over a 70° range of motion. The average of the peak power values calculated from the 46th to 50th contractions during the fatigue task was normalized to the prefatigue peak power value, which was defined as neuromuscular fatigue resistance. Neuromuscular fatigue resistance was negatively associated with prefatigue maximal power output (r = -.530) but not with prefatigue maximal voluntary contraction torque (r = -.252). This result highlights a trade-off between prefatigue maximal power output and neuromuscular fatigue resistance, implying that an improvement in maximal power output might have a negative impact on neuromuscular fatigue resistance.

Association of age-related decrease in intracellular-to-total water ratio with that in explosive strength of the plantar flexors: a cross-sectional study.

BACKGROUND: We aimed to investigate the association of age-related differences in the intracellular-to-total water ratio with explosive strength of the plantar flexors. METHODS: A total of 60 young (21-33 years) and older (64-83 years) individuals were recruited. Intracellular- (ICW) and total-water (TW) content within the right leg was evaluated by bioelectrical impedance spectroscopy as indicators of muscle cell mass and whole muscle mass within the segment, respectively. ICW divided by TW (ICW/TW) was calculated as an index of the occupancy of muscle cells within whole muscle. Rate of torque development (RTD) and electromyography (EMG) activity during maximal voluntary isometric plantar flexion were measured as indicators of explosive muscle strength and neuromuscular activity, respectively. RTD was calculated from three time windows of 0-50, 50-100, and 100-200 ms. Time-to-peak torque (TPT) was assessed from evoked twitch contraction. RESULTS: Compared with young participants, older participants showed lower ICW/TW (-7%, P < 0.001), RTD (-25 to -40%, P = 0.003 to 0.001), and longer TPT (+11%, P < 0.001). ICW/TW associated positively with RTD (r = 0.377 to 0.408, P = 0.004 to 0.001) and negatively with TPT (r = -0.392, P = 0.002), but not with EMG activity. RTD was associated positively with EMG for each time window (r = 0.527 to 0.607, P < 0.001). CONCLUSIONS: These results indicate that ICW/TW may be a useful predictor of the age-related decrease in RTD, and that the decrease in ICW/TW with age may reflect age-associated changes in intrinsic contractile properties.

Power attenuation from restricting range of motion is minimized in subjects with fast RTD and following isometric training.

Time-dependent measures consisting of rate of torque development (RTD), rate of velocity development (RVD), and rate of neuromuscular activation can be used to evaluate explosive muscular performance, which becomes critical when performing movements throughout limited ranges of motion (ROM). In this study, we investigated how restricting ROM influences power production while also exploring the relationship with time-dependent measures before and after isometric resistance training. Using a HUMAC NORM dynamometer, seven males (27 ± 7 yr) and six females (22 ± 3 yr) underwent 8 wk of maximal isometric dorsiflexion training 3 days/wk. One leg was trained at 0° [short-muscle tendon unit (MTU) length] and the other at 40° of plantar flexion (long-MTU length). RTD and rate of neuromuscular activation were evaluated during "fast" maximal isometric contractions. Power, RVD, and rate of neuromuscular activation were assessed during maximal isotonic contractions in four conditions [small (40°-30° of plantar flexion) ROM at 10% and 50% MVC; large (40°-0° of plantar flexion) ROM at 10% and 50% MVC] for both legs, pre- and posttraining. Despite no change in rate of neuromuscular activation following training, peak power, RTD, and RVD increased at both MTU lengths (P < 0.05). Strong relationships (R2 = 0.73) were observed between RTD and peak power in the small ROM, indicating that fast time-dependent measures are critical for optimal performance when ROM is constrained. Meanwhile, strong relationships (R2 = 0.90) between RVD and power were observed at the 50% load, indicating that RVD is critical when limited by load and ROM is not confined. Maximal isometric dorsiflexion training can be used to improve time-dependent measures (RTD, RVD) to minimize power attenuation when ROM is restricted.NEW & NOTEWORTHY Power output was greater in the unrestricted than restricted ROM, and there were strong relationships between rate of torque development (RTD) and velocity development (RVD) with peak power. RTD and RVD had the strongest relationships with power when ROM was restricted and unrestricted, respectively. Following 8 wk of isometric training, discrepancies in power between restricted and unrestricted ROM were reduced. Increasing RTD through isometric training increased power in dynamic movements, especially when ROM was restricted.

Contribution of muscle stiffness of the triceps surae to passive ankle joint stiffness in young and older adults.

This study aimed to investigate whether triceps surae muscle stiffness is associated with passive ankle joint stiffness in 40 young (21-24 years) and older (62-83 years) males. Using ultrasound shear wave elastography, the shear modulus of each muscle of the triceps surae (the medial [MG], lateral gastrocnemius [LG], and soleus [Sol]) was assessed as muscle stiffness at the ankle neutral position (NP) and 15-degree dorsiflexed position (DF15) with the knee fully extended. Passive ankle joint stiffness at the NP and DF15 was calculated as the gradient of the angle-torque relationship at each joint angle during passive ankle dorsiflexion at 1°âˆ™s-1 controlled by using an isokinetic dynamometer. Passive ankle joint stiffness was normalized by the body mass. There was no correlation between the absolute ankle joint stiffness and muscle shear modulus of triceps surae in the young and older groups at the NP (r ≤ 0.349, p ≥ 0.138). Significant positive correlations between absolute ankle joint stiffness and muscle shear modulus at DF15 were observed for MG and Sol in the young group (r ≥ 0.451, p ≤ 0.044) but not in the older group. The normalized ankle joint stiffness at the NP was significantly positively correlated with the LG shear modulus in young participants and with the MG and LG shear modulus in older participants (r ≥ 0.466 and p ≤ 0.039). There were significant positive correlations between the normalized ankle joint stiffness and the muscle shear modulus of the triceps surae at DF15 in young and older participants (r ≥ 0.464 and p ≤ 0.040), except for the MG shear modulus in older participants (r = 0.419 and p = 0.066). These results suggest that the material properties of the entire triceps surae, even Sol, which is the most compliant muscle among the triceps surae, affect passive ankle joint stiffness, especially when the triceps surae is lengthened and body size is considered.

Muscle Damage Indicated by Maximal Voluntary Contraction Strength Changes From Immediately to 1 Day After Eccentric Exercise of the Knee Extensors.

The present study examined if the magnitude of changes in indirect muscle damage markers could be predicted by maximal voluntary isometric contraction (MVIC) torque changes from immediately to 1 day after eccentric exercise. Twenty-eight young men performed 100 maximal isokinetic (60°/s) eccentric contractions of the knee extensors. MVIC torque, potentiated doublet torque, voluntary activation (VA) during MVIC, shear modulus of rectus femoris (RF), vastus medialis and lateralis, and muscle soreness of these muscles were measured before, immediately after, and 1-3 days post-exercise. Based on the recovery rate of the MVIC torque from immediately to 1-day post-exercise, the participants were placed to a recovery group that showed an increase in the MVIC torque (11.3-79.9%, n = 15) or a no-recovery group that showed no recovery (-71.9 to 0%, n = 13). No significant difference in MVIC torque decrease immediately post-exercise was found between the recovery (-33 ± 12%) and no-recovery (-32 ± 9%) groups. At 1-3 days, changes in MVIC torque (-40 to -26% vs. -22 to -12%), potentiated doublet torque (-37 to -22% vs. -20 to -9%), and proximal RF shear modulus (29-34% vs. 8-15%) were greater (p < 0.05) for the no-recovery than recovery group. No significant group differences were found for muscle soreness. The recovery rate of MVIC torque was correlated (p < 0.05) with the change in MVIC torque from baseline to 2 (r = 0.624) or 3 days post-exercise (r = 0.526), or peak change in potentiated doublet torque at 1-3 days post-exercise from baseline (r = 0.691), but not correlated with the changes in other dependent variables. These results suggest that the recovery rate of MVIC torque predicts changes in neuromuscular function but not muscle soreness and stiffness following eccentric exercise of the knee extensors.