Search

Abstract Background Sarcopenic obesity (SO) is defined as a decrease in lean body mass and an increase in body fat mass (BFM) due to aging. Detecting SO in elderly women is important from the perspective of extending healthy life expectancy. While various indices of SO are currently used, there is no global consensus regarding diagnostic criteria for SO. This study aimed to examine the relationship between obesity indices (waist circumference (WC), body mass index (BMI), and body fat percentage (BFP)) and sarcopenia indices (total body muscle mass (TBM), appendicular lean mass (ALM), skeletal mass index (SMI)), and physical function (gait speed (GS), handgrip strength (HGS)). Methods Subjects were 170 community-dwelling healthy elderly women aged 65–79 years (mean: 72.7 ± 5.78 years) who underwent measurements for WC, BMI, and BFP. A WC of ≥ 90cm was defined as the obese group, BMI was determined as weight (kg) divided by height squared (m2) and a cutoff of ≥ 25 kg/m2 was used to define the obesity group. BFM was measured using the bioelectrical impedance analysis (BIA) method and BFP was calculated from body weight and a cutoff of ≥ 30% was used to define the obesity group. TBM and ALM (kg) were measured using the BIA method, ALM (kg) was corrected for height (m2) to obtain SMI (kg/m2). Physical function was assessed by GS and HGS, which were measured by the 5-m walk test and a digital grip strength meter, respectively. Results When obesity was assessed using BMI, WC and BFP, obese individuals had higher TBM, ALM and SMI, and lower GS among the sarcopenia indicators. HGS did not differ significantly between the non-obese and obese groups. Conclusion Our findings suggest HGS is thought to reflect muscle strength without being affected by obesity indices, suggesting that it may be useful in detecting possible sarcopenia in obese individuals.

Abstract This study aimed to evaluate the presence of adipose tissue surrounding the flexor hallucis longus (FHL) tendon through gross dissection and magnetic resonance imaging (MRI). Grossly, we observed the FHL tendon and surrounding tissues in nine cadavers. Using MRI, we quantitatively evaluated each tissue from the horizontal plane in 40 healthy ankles. Macroscopic autopsy revealed the presence of adipose tissue behind the ankle joint between the FHL and fibula, and horizontal cross-sections showed an oval-shaped adipose tissue surrounding the tendon. The cross-sectional area on MRI was 14.4 mm2 (11.7–16.7) for the FHL tendon and 120.5 mm2 (100.3–149.4) for the adipose tissue. Additionally, the volume of the adipose tissue was 963.3 mm3 (896.2–1115.6). There is an adipose tissue around FHL tendon and maybe this close anatomical relationship might influence the function of the tendon and be involved in its pathologies.

Abstract Background Locomotive syndrome (LS) is a condition of reduced mobility due to a disorder of the locomotive system. Increasing moderate to vigorous physical activity (MVPA) has been recommended to prevent LS. However, to increase daily MVPA is difficult for older people with LS. The MVPA consists of not only locomotive activities such as walking but also non-locomotive activities such as household activities. The aim of this study was to examine the associations between locomotive/non-locomotive MVPA and physical performance in older females with and without LS. Methods Participants of this cross-sectional study were 143 older community-dwelling Japanese females. The participants were divided into two groups based on the results of the stand-up test: the normal group (NL) (n = 86) and the LS group (n = 57). Both the locomotive and non-locomotive PA seperately measured with its intensity. The intensity of physical activity (PA) was calculated as METs and classified as sedentary behavior (SB 1–1.5 metabolic equivalent tasks (METs)), low-intensity physical activity (LPA 1.6–2.9 METs), and MVPA (≥ 3 METs). For example, locomotive LPA is slow walking speed of 54 m/min, and locomotive MVPA is walking speed of 67 m/min. While non-locomotive LPA is office work and cooking, non-locomotive MVPA is housecleaning. Physical function was evaluated by handgrip strength, walking speed, and 2-step test. Results Walking speed, hand-grip strength, 2-step test, daily step counts, and all PA measurements were not significantly different between two groups. In the LS, locomotive MVPA (r = 0.293, p < 0.05) and total MVPA (r = 0.299, p < 0.05) was significantly correlated with walking speed, but not in the NL. Conclusions Walking speed was positively correlated with locomotive MVPA and total MVPA in the LS group, but not in NL group. This result suggests that slow walking speed in older people with LS occur in connection with lower locomotive MVPA and total MVPA.

Abstract Background Plantar intrinsic foot muscles (PIFMs) are composed of 10 muscles and play an essential role in achieving functional diversity in the foot. Previous studies have identified that the morphological profiles of PIFMs vary between individuals. The morphological profiles of a muscle theoretically reflect its output potentials: the physiological cross‐sectional area (PCSA) of a muscle is proportional to its maximum force generation, and the muscle fiber length (FL) is its shortening velocity. This implies that the PCSA and FL may be useful variables for characterizing the functional diversity of the individual PIFM. The purpose of this study was to examine how individual PIFMs can be classified based on their PCSA and FL. Methods In 26 healthy young adult males, the muscle volume and muscle length of seven PIFMs (abductor hallucis, ABDH; abductor digiti minimi, ABDM; adductor hallucis oblique head, ADDH‐OH; ADDH transverse head, ADDH‐TH; flexor digitorum brevis, FDB; flexor hallucis brevis, FHB; quadratus plantae, QP) were measured using magnetic resonance imaging. The PCSA and FL of each of the seven PIFMs were then estimated by combining the data measured from the participants and those of muscle architectural parameters documented from cadavers in previous studies. A total of 182 data samples (26 participants × 7 muscles) were classified into clusters using k‐means cluster analysis. The optimal number of clusters was evaluated using the elbow method. Results The data samples of PIFMs were assigned to four clusters with different morphological profiles: ADDH‐OH and FHB, characterised by large PCSA and short FL (high force generation and slow shortening velocity potentials); ABDM and FDB, moderate PCSA and moderate FL (moderate force generation and moderate shortening velocity potentials); QP, moderate PCSA and long FL (moderate force generation and rapid shortening velocity potentials); ADDH‐TH, small PCSA and moderate FL (low force generation and moderate shortening velocity potentials). ABDH components were assigned equivalently to the first and second clusters. Conclusions The approach adopted in this study may provide a novel perspective for interpreting the PIFMs' function based on their maximal force generation and shortening velocity potentials.

This study aimed to compare different ultrasound devices with magnetic resonance spectroscopy (MRS) to quantify muscle lipid content from echo intensity (EI). Four different ultrasound devices were used to measure muscle EI and subcutaneous fat thickness in four lower-limb muscles. Intramuscular fat (IMF), intramyocellular (IMCL) and extramyocellular lipids (EMCL) were measured using MRS. Linear regression was used to compare raw and subcutaneous fat thickness-corrected EI values to IMCL, EMCL and IMF. IMCL had a poor correlation with muscle EI (r = 0.17–0.32, NS), while EMCL (r = 0.41–0.84, p < 0.05–p < 0.001) and IMF (r = 0.49–0.84, p < 0.01–p < 0.001) had moderate to strong correlation with raw EI. All relationships were improved when considering the effect of subcutaneous fat thickness on muscle EI measurements. The slopes of the relationships were similar across devices, but there were some differences in the y-intercepts when raw EI values were used. These differences disappeared when subcutaneous fat thickness-corrected EI values were considered, allowing for the creation of generic prediction equations (r = 0.41–0.68, p < 0.001). These equations can be used to quantify IMF and EMCL within lower limb muscles from corrected-EI values in non-obese subjects, regardless of the ultrasound device used.

Abstract Background Older adults are known to have more pronated foot posture and decreased toe flexor strength (TFS), as well as decreased mobility in daily life compared to young adults. Although foot posture is reported to be an influential factor for walking biomechanics in young adults, there is less information on this subject in older adults. Age-related reduction in TFS is shown to be associated with impairments of functional performance, but it is poorly understood whether foot posture influences the relationships between TFS and functional performances. Therefore, the present study aimed to elucidate this concern by examining older women. Methods Seventy community-dwelling older women (76.8 ± 4.4 years) voluntarily participated in this study. Foot posture was evaluated by the 6-item foot posture index (FPI). Based on the FPI score, participants were allocated to pronated, neutral, or supinated group (n = 33, 26, and 11, respectively). TFS was assessed using a toe grip dynamometer in a seated position. Scores of 30-s chair stand, timed up-and-go, 5-m comfortable-speed walking, and static balance tests were determined to evaluate functional performances. Pearson’s correlation coefficients were computed to examine the relationships between TFS and functional performances in each group. Results TFS positively correlated with comfortable walking speed in the pronated (r = 0.37, p = 0.03) and supinated (r = 0.76, p

Abstract Background The size of the plantar intrinsic and extrinsic foot muscles has been shown to be associated with toe flexor strength (TFS). Previous studies adopted the size of limited plantar intrinsic foot muscles or a compartment containing several muscles as an independent variable for TFS. Among the plantar intrinsic and extrinsic foot muscles, therefore, it is unclear which muscle(s) primarily contributes to TFS production. The present study aimed to clarify this subject. Methods In 17 young adult men, a series of anatomical cross‐sectional area of individual plantar intrinsic and extrinsic foot muscles was obtained along the foot length and the lower leg length, respectively, using magnetic resonance imaging. Maximal anatomical cross‐sectional area (ACSAmax) and muscle volume (MV) for each constituent muscle of the plantar intrinsic foot muscles (flexor hallucis brevis; flexor digitorum brevis, FDB; abductor hallucis; adductor hallucis oblique head, ADDH‐OH; adductor hallucis transverse head, ADDH‐TH; abductor digiti minimi; quadratus plantae) and extrinsic foot muscles (flexor hallucis longus; flexor digitorum longus) were measured. TFS was measured with a toe grip dynamometry. Results TFS was significantly associated with the ACSAmax for each of the ADDH‐OH (r = 0.674, p = 0.003), ADDH‐TH (r = 0.523, p = 0.031), and FDB (r = 0.492, p = 0.045), and the MV of the ADDH‐OH (r = 0.582, p = 0.014). As for the ADDH‐OH, the correlation coefficient with TFS was not statistically different between ACSAmax and MV (p = 0.189). Stepwise multiple linear regression analysis indicated that ACSAmax and MV of the ADDH‐OH alone explained 42 and 29%, respectively, of the variance in TFS. Conclusion The ADDH‐OH is the primary contributor to TFS production among the plantar intrinsic and extrinsic foot muscles as the result of the stepwise multiple linear regression analysis.

Change of direction speed (CODS) is essential for basketball performance, extensively assessed by various tests. This review aimed to summarize the CODS test varieties for basketball players on publications until 2019 and identify recent trends regarding what types of tests have gained attention in the 2010s. Electronic literature searches were conducted using three databases with relevant keywords. 104 studies were found eligible, conducting CODS tests 159 times in total with 48 test varieties. To facilitate distinctions between the tests, each test was categorized into one of three types based on the distinctive movement characteristics and changing angles as follows: Defensive (involving lateral shuffling), 180°-turn (exerting only 180°-turns), and Cutting (performing diagonal- or side-cut). We then counted the number of publications and adopted times reported per year for each test, and calculated the adoption rate for each categorized test type. The first CODS test performed in basketball players was the T-Test, reported in 1991, and this was the most commonly adopted test (44/159 times). The 2010s saw abrupt increases in the number of publications (1990s-2000s-2010s: 5-9-90) and test varieties (4-7-44). The adoption rates in the 2010s were similar among the three types (i.e., Defensive/180°-turn/Cutting: 37%/30%/33%), with the Cutting type gradually increasing over the last three decades (1990s-2000s-2010s: 0%-9%-33%). These results suggest that while CODS performances in basketball players are increasingly studied with various tests, recent studies give equal weight to all of the three categorized test types, with increasing adoption of the Cutting type, to assess specific CODS performances.

Toe muscular strength plays an important role in enhancing athletic performance because the forefoot is the only part of the body touching the ground. In general, muscular strength increases with age throughout adolescence, and sex-related difference in muscular strength becomes evident during childhood and adolescence. However, toe muscular strength is known to be levelled off after late adolescence in both sexes. For adolescent populations, therefore, the association of toe muscular strength with physical performance might differ with age and/or sex. This study aimed to investigate differences in relationships between toe muscular strength and vertical jump performance across sex and age in adolescent populations. The maximum isometric strength of the toe muscles and vertical jump height (VJ) were assessed in 479 junior high school students (JH) aged 12–14 years (243 boys and 236 girls) and 465 high school students (HS) aged 15–18 years (265 boys and 200 girls). Two types of measurements were performed to evaluate the toe muscular strength: toe gripping strength (TGS) with the metatarsophalangeal joint in the plantar flexed position and toe push strength (TPS) with the metatarsophalangeal joint in the dorsiflexed position. TGS and TPS were normalized to body weight. Two-way ANOVA showed that TGS had significant main effects of sex (boys > girls) and age (HS > JH) while TPS only had a significant main effect of sex (boys > girls). When the effects of sex and age were separately analyzed, VJ was significantly correlated with TGS in JH girls, HS girls, and JH boys (r = 0.253–0.269, p < 0.05), but not in HS boys (r = 0.062, p = 0.3351). These results suggest that toe muscular strength is relatively weakly associated with vertical jump performance in adolescent boys and girls, but the association would not be established in high school boys.

Abstract Background Age-related reduction in bone mineral density (BMD) is generally accelerated in women after menopause, and could be even more pronounced in individuals with sarcopenia. Light-load power training with a low number of repetitions would increase BMD, significantly reducing bone loss in individuals at risk of osteoporosis. This study investigated the effects of low-repetition, light-load power training on BMD in Japanese postmenopausal women with sarcopenia. Methods The training group (n = 7) followed a progressive power training protocol that increased the load with a weighted vest, for two sessions per week, over the course of 6 weeks. The training exercise comprised five kinds of exercises (squats, front lunges, side lunges, calf raises, and toe raises), and each exercise contained eight sets of three repetitions with a 15-s rest between each set. The control group (n = 8) did not undergo any training intervention. We measured BMD, muscle strength, and anthropometric data. Results Within-group changes in pelvis BMD and knee extensor strength were significantly greater in the training group than the control group (p = 0.029 and 0.030 for pelvis BMD and knee extensor strength, respectively). After low-repetition, light-load power training, we noted improvements in pelvis BMD (1.6%) and knee extensor strength (15.5%). No significant within- or between-group differences were observed for anthropometric data or forearm BMD. Conclusions Six weeks of low-repetition, light-load power training improved pelvis BMD and knee extensor strength in postmenopausal women with sarcopenia. Since this training program does not require high-load exercise and is therefore easily implementable as daily exercise, it could be an effective form of exercise for sedentary adults at risk for osteoporosis who are fearful of heavy loads and/or training that could cause fatigue. Trial Registration This trial was registered with the University Hospital Medical Information Network on 31 October 2016 ( UMIN000024651 ).

Exercise-induced changes in executive function affect the control of action in a dynamic environment. This study aimed to examine the effect of sustained high-intensity exercise on executive function. Nine healthy male and female participants (age, 21-28 years) completed an exercise session with 65-min treadmill running at 75% VO2max. Executive function was assessed before and after exercise with the Stroop Color and Word Test that included congruent and incongruent conditions. The reaction time and response accuracy of the test were measured, and the task difficulty was controlled by adjusting the stimulus duration so that each participant could maintain at least 80% response accuracy to exclude the effect of a speed–accuracy trade-off. The levels of plasma norepinephrine and adrenocorticotropic hormone were examined. A significant interaction with the reaction time was found (condition × time, P = 0.024), in which the reaction time significantly increased after exercise only in the incongruent condition (P = 0.019). The response accuracy was not significantly different between before and after exercise in both conditions, which indicated that the response accuracy was controlled as intended. The levels of plasma norepinephrine and adrenocorticotropic hormone were significantly increased after exercise (P < 0.05). These results demonstrated that the reaction time in the incongruent condition increased after sustained high-intensity exercise with a cognitive function test with the response accuracy controlled, indicating a decline in executive function. Increased levels of plasma norepinephrine and adrenocorticotropic hormone may contribute, at least in part, to such decline in executive function.

Repetitive mechanical load applied to a body part may lead to hypertrophy of its muscles. If a movement requires asymmetric activation of bilateral muscles, this may result in differences in muscle size between the sides. This study aimed to investigate the degree of bilateral differences in the trunk muscle volume of golfers by comparing with non-golfers. Seventeen male right-handed golfers and eleven (nine right- and two left-handed) non-golfers participated. Trunk muscle volume was determined using magnetic resonance imaging, and the degree of asymmetry was calculated as the ratio of trunk muscle volume on the left to trunk muscle volume on the right side in right-handers and vice-versa in left-handers. Golfers had significantly larger lateral abdominal wall (LA) muscle volume than non-golfers: 12.36 ± 1.12 vs. 9.96 ± 0.94 cm3/kg; erector spinae: 9.12 ± 1.16 vs. 7.88 ± 0.84 cm3/kg; psoas major (PM): 6.27 ± 0.88 vs. 5.51 ± 0.98 cm3/kg; rectus abdominis (RA): 4.15 ± 0.54 vs. 3.50 ± 0.64 cm3/kg; and multifidus: 3.61 ± 0.41 vs. 3.05 ± 0.40 cm3/kg (p < 0.05). The degree of bilateral asymmetry of the LA, PM, and RA volume was significantly greater in golfers than in non-golfers (LA: -8.63 ± 7.40% vs. 1.94 ± 2.76%; PM: -9.10 ± 5.25% vs. -0.48 ± 5.96%; RA: 6.36 ± 6.50% vs. -2.12 ± 9.64%, respectively, p < 0.05). Right-handed golfers had greater left LA and PM volume compared to the right (LA: 5.89 ± 0.55 vs. 6.48 ± 0.65 cm3/kg; PM: 3.00 ± 0.42 vs. 3.27 ± 0.47 cm3/kg; p < 0.05) and had greater right RA volume compared to the left (2.15 ± 0.32 vs. 2.00 ± 0.24 cm3/kg, p < 0.05). These findings suggest that skilled, long-term golfers develop large volume and bilateral asymmetry of their trunk muscles.

Background A decline in executive function could have a negative influence on the control of actions in dynamic situations, such as sports activities. Mouth rinsing with a carbohydrate solution could serve as an effective treatment for preserving the executive function in exercise. The purpose of this study was to examine the effects of mouth rinsing with a carbohydrate solution on executive function after sustained moderately high-intensity exercise. Methods Eight young healthy participants completed 65 min of running at 75% V̇O2max with two mouth-rinsing conditions: with a carbohydrate solution (CHO) or with water (CON). Executive function was assessed before and after exercise by using the incongruent task of the Stroop Color and Word Test. The levels of blood glucose; and plasma adrenocorticotropic hormone (ACTH), epinephrine, and norepinephrine (NE) were evaluated. A two-way repeated-measures ANOVA, with condition (CHO and CON) and time (pre-exercise and post-exercise) as factors, was used to examine the main and interaction effects on the outcome measures. Results The reaction time in the incongruent condition of the Stroop test significantly increased after exercise in CON (pre-exercise 529 ± 45 ms vs. post-exercise 547 ± 60 ms, P = 0.029) but not in CHO (pre-exercise 531 ± 54 ms vs. post-exercise 522 ± 80 ms), which resulted in a significant interaction (condition × time) on the reaction time (P = 0.028). The increased reaction time in CON indicates a decline in the executive function, which was attenuated in CHO. Increases in plasma epinephrine and NE levels demonstrated a trend toward attenuation accompanying CHO (P

Experienced sprinters are specifically adapted to pre-planning an advanced motor program. Herein, sprinters are able to immediately accelerate their center of mass forward with a whole-body coordinated motion, following a steady state crouched position. We examined the effect of variable timing of reaction signals on multiple joint reaction times (RT) and whole-body RT for specialist sprinters. Twenty well-experienced male sprinters performed five start-dashes from a block start under five variable foreperiod (FP) length conditions (1.465, 1.622, 1.780, 1.938, and 2.096 s), with trials randomly timed between a warning and an imperative tone. Participants’ sprinting motion and ground reaction forces of their four limbs during the block start were measured simultaneously. Whole-body RT was significantly shorter when FP length was longer; the values of whole-body RT were 117 ± 5 ms, 129 ± 5 ms, 125 ± 4 ms, 133 ± 6 ms, and 156 ± 8 ms in the 2.096, 1.938, 1.780, 1.622, and 1.465-s FP-length conditions, respectively. A repeated-measures analysis of variance found a significant joint-by-FP length interaction in joint-moment RT. These findings suggest that FP length affects coordinated motion in four limbs and whole-body RT. This information will be able to lead to new methods for start signals in sprint running events and advance our understanding of the association between FP length and dynamic coordinated motion.

This study aimed to clarify the effect of widened stance width at the set position during the block start phase in sprint running on kinematics and kinetics at the hip joint and block-induced power. Fourteen male sprinters volunteered to participate in this study. They performed three block-start trials with a normal stance width (25 ± 1 cm, normal condition) and a widened stance width (45 ± 2 cm, widened condition) at the set position. The block start movements were recorded at 250 Hz with high-speed cameras and the ground reaction forces at 1250 Hz with force plates. During the block phase in the widened condition, the hip abduction and external rotation angles in both legs were significantly larger and smaller, respectively, than those in the normal condition. The positive peak value of the hip power in the rear leg was significantly greater in the widened condition than that in the normal condition. However, no significant difference was seen in the normalized block-induced power between the widened and normal conditions. We conclude that a widened stance width at the set position affects the hip-joint kinematics and rear hip power generation during the block start phase, but no effect on the block-induced power when considering sprinting performance during the whole block start phase.

Sarcopenia has never been diagnosed based on site-specific muscle loss, and little is known about the relationship between site-specific muscle loss and metabolic syndrome (MetS) risk factors. To this end, this cross-sectional study aimed to investigate the relationship between site-specific muscle size and MetS risk factors. Subjects were 38 obese men and women aged 40-82 years. Total body fat and lean body mass were assessed by whole-body dual-energy X-ray absorptiometry (DXA) scan. Muscle thickness (MTH) was measured using B-mode ultrasound scanning in six body regions. Subjects were classified into general obesity (GO) and sarcopenic obesity (SO) groups using the threshold values of one standard deviation below the sex-specific means of either MTH or skeletal muscle index (SMI) measured by DXA. MetS risk score was acquired by standardizing and summing the following continuously distributed variables: visceral fat area, mean blood pressure, HbA1c, and serum triglyceride / high density lipoprotein cholesterol, to obtain the Z-score. Multiple regression analysis revealed that the MetS risk score was independently associated with abdominal MTH in all subjects, but not with MTH in other muscle regions, including the thigh. Although HbA1c and the number of MetS risk factors in the SO group were significantly higher than those in the GO group, there were no significant differences between GO and SO groups as defined by SMI. Ultrasound-derived abdominal MTH would allow a better assessment of sarcopenia in obese patients and can be used as an alternative to the conventionally-used SMI measured by DXA.

Muscle force is potentiated by countermovement; this phenomenon is called stretch-shortening cycle (SSC) effect. In this study, we examined the factors strongly related to SSC effect in vivo, focusing on tendon elongation, preactivation, and residual force enhancement. Twelve healthy men participated in this study. Ankle joint angle was passively moved by a dynamometer, with a range of motion from 15° dorsiflexion (DF) to 15° plantarflexion (PF). Muscle contraction was evoked by electrical stimulation, with stimulation timing adjusted to elicit three types of contraction: (1) concentric contraction without preliminary contraction (CON), (2) concentric contraction after preliminary eccentric contraction (ECC), and (3) concentric contraction after preliminary isometric contraction (ISO). Joint torque was recorded at DF5°, PF0°, and PF5°, respectively. SSC effect was calculated as the ratio of joint torque obtained in ECC or ISO with respect to that obtained in CON at the aforementioned three joint angles. SSC effect was prominent in the first half of movement in both ECC (DF5°, 329.3 ± 101.2%; PF0°, 159.2 ± 29.4%; PF5°, 125.5 ± 20.8%) and ISO (DF5°, 276.4 ± 87.0%; PF0°, 134.5 ± 24.5%; PF5°, 106.8 ± 18.0%) conditions. SSC effect was significantly larger in ECC than in ISO at all joint angles (P < 0.001). Even without preliminary eccentric contraction (i.e., ISO condition), SSC effect was clearly large, indicating that a significant part of SSC effect is derived from preactivation. However, the active lengthening-induced force potentiation mechanism (residual force enhancement) also contributes to SSC effect.

To elucidate the effects of endurance training on circulating irisin levels in young and middle-aged/older adults, and to determine the association between endurance training-induced alteration of irisin and reduction in body fat. Twenty-five healthy young (age 21 ± 1 years; 16 men, 9 women) and 28 healthy middle-aged/older adults (age 67 ± 8 years; 12 men, 16 women) participated in the study. Each age cohort was divided into two groups: the endurance-training group (14 young, 14 middle-aged/older) and the control group. Subjects in the training groups completed an 8-week endurance-training program (cycling at 60-70% peak oxygen uptake [V̇O2peak] for 45 min, 3 days/week). Before and after the intervention, we evaluated serum irisin level, V̇O2peak, and body composition. The increase in V̇O2peak in the young and middle-aged/older training groups after the intervention period was significantly greater than those in the young and middle-aged/older control groups (P < 0.05). Serum irisin level was significantly increased in the middle-aged/older training group after the intervention period (P < 0.01), but not in the young training group. Furthermore, in the middle-aged/older training group, the endurance training-induced reduction in visceral adipose tissue area was negatively correlated with the change in serum irisin level (r = -0.54, P < 0.05). These results suggest a possible role for secreted irisin in the exercise-induced alteration of abdominal visceral fat in middle-aged and older adults.

Abstract Background The aims of this study were to investigate the relationships between the maximum isometric toe flexor muscle strength (TFS) and cross‐sectional area (CSA) of the plantar intrinsic and extrinsic muscles and to identify the major determinant of maximum TFS among CSA of the plantar intrinsic and extrinsic muscles. Methods Twenty six young healthy participants (14 men, 12 women; age, 20.4 ± 1.6 years) volunteered for the study. TFS was measured by a specific designed dynamometer, and CSA of plantar intrinsic and extrinsic muscles were measured using magnetic resonance imaging (MRI). To measure TFS, seated participants optimally gripped the bar with their toes and exerted maximum force on the dynamometer. For each participant, the highest force produced among three trials was used for further analysis. To measure CSA, serial T1‐weighted images were acquired. Results TFS was significantly correlated with CSA of the plantar intrinsic and extrinsic muscles. Stepwise multiple linear regression analyses identified that the major determinant of TFS was CSA of medial parts of plantar intrinsic muscles (flexor hallucis brevis, flexor digitorum brevis, quadratus plantae, lumbricals and abductor hallucis). There was no significant difference between men and women in TFS/CSA. Conclusions CSA of the plantar intrinsic and extrinsic muscles is one of important factors for determining the maximum TFS in humans.

Purpose: Morphological differences between the two primary great toe flexors - flexor hallucis longus (FHL) and flexor hallucis brevis (FHB) - likely drive differences in how these muscles contribute to functional toe flexor torque production. The aim of the study was to investigate FHL and FHB activation in two isometric toe flexion tasks - one called a "toe-pushing" task with the metatarsophalangeal (MTP) joints dorsiflexed and the interphalangeal (IP) joints in neutral and another called a "toe-gripping" task with the MTP joints in neutral and flexed IP joints. Methods: Twenty participants' FHL and FHB muscles were instrumented with intramuscular electromyography electrodes. Muscle activation was normalized to a maximum voluntary contraction and compared between the two isometric toe flexor force production tasks. Results: Overall, participants utilized these two toe flexors completely differently in the two tasks. In the toe-gripping task, the FHL was activated to a much greater extent than the FHB. In fact, 18 our of 20 participants activated FHL at more than 70% maximum voluntary contraction and half of participants activated FHB at less than 10%. In contrast, muscle activation during the toe-pushing task appeared more reliant on the FHB for most participants. Conclusions: Different contributions from the FHL and FHB to toe flexor force production in these two tasks are potentially driven by differences in muscle functional length among other factors. These findings help to inform the selection of rehabilitation and training exercises meant to preferentially target intrinsic or extrinsic foot musculature. [ABSTRACT FROM AUTHOR]