Corrigendum: The relationships of sleep duration and inconsistency with the athletic performance of collegiate soft tennis players.

[This corrects the article DOI: 10.3389/fpsyg.2022.791805.].

Association between perceived exertion and executive functions with serve accuracy among male university tennis players: A pilot study.

Serve in tennis is a very important strokes and is positively correlated with the rankings of the Association of Tennis Professionals ranking. This study investigated the associations between time-course changes in the ratings for perceived exertion, executive function, and second serve accuracy during 30-min tennis exercise sessions. Eleven Japanese male tennis players participated in the study, and their executive function and second serve performance were evaluated using the paper version of the Stroop Color and Word Test, followed by a serve performance test. The participants took part in a 30-min tennis exercise program and performed the Stroop Color and Word Test, heart rate (HR) check, and second serve accuracy test before and after the tennis exercise. Pearson correlation was used to determine the relationships between the ratings for perceived exertion, interference scores on Stroop Color and Word Test performance, and second serve performance. Post exercise, the rating of perceived exertion tended to correlate with serve accuracy (r = -0.57, p = 0.07) and interference score (r = 0.65, p = 0.03). The pre-to-post changes in second serve accuracy were negatively associated with the changes in interference score (r = -0.54, p = 0.08) and interference score in the posttest (r = -0.73, p = 0.01). The results suggest that time-course changes in executive function when playing tennis are positively associated with the accuracy of the second serve. These findings expand the previous knowledge regarding the positive association between time-course changes in executive functions and percentage of points won when playing tennis by including more specific skills (i.e., second serve accuracy).

The Relationships of Sleep Duration and Inconsistency With the Athletic Performance of Collegiate Soft Tennis Players.

We evaluated the relationships of daily sleep duration and inconsistency with soft tennis competitive performance among 15 healthy collegiate soft tennis players (13 male, 2 female, mean age = 19.7 ± 0.8 years, height = 170.8 ± 7.3 cm, weight = 60.3 ± 5.6 kg, soft tennis experience = 8.7 ± 2.0 years). Sleep duration and inconsistency were determined by a 50-day sleep diary, which recorded sleep and wake times of sleep. Soft tennis athletic performance was evaluated by a service and baseline stroke accuracy test and the spider run test. Mean sleep duration was 7.4 ± 1.7 h. No correlation was found between long-term mean sleep duration and athletic performance. But inconsistency in sleep duration (SD of sleep duration) was inversely correlated with service score after controlling for soft tennis experience and sex (r = -0.56, p = 0.046). There was no significant relationship between sleep inconsistency and other athletic performance. This result indicates that reducing the instability of sleep duration (i.e., sleep regular hours) in the long-term may have a positive effect on soft tennis players' service performance. Although participants' current mean sleep duration (7.4 h) was not as sufficient as the recommendation in sleep extension experiments (9-10 h), it revealed the importance for athletes to maintain regular sleep in daily life.

Aß Influx into the Blood Evoked by Different Blood Aß Removal Systems: A Potential Therapy for Alzheimer's Disease.

PURPOSE: Amyloid-ß (Aß) is a brain protein that causes Alzheimer's disease. We have revealed that extracorporeal blood Aß-removal systems evoked a large Aß influx into the blood. This study investigated the system that is more effective in evoking Aß influx. METHODS: Aß removal activities were compared between hexadecyl-alkylated cellulose beads (HexDC) and fragments of polysulfone hollow fibers (PSf-HFs) in mini-columns to eliminate the filtration effect. Then, adsorptive filtration systems were adapted for PSf hemodialyzers to enhance Aß adsorption on micropores in the wall of hollow fibers. Plasma Aß concentrations of patients with renal failure were analyzed during treatment with PSf hemodialyzers alone for 8 h or tandemly connected HexDC and PSf hemodialyzers for 4 h. RESULTS: In the in vitro study, Aß removal efficiency for HexDC was approximately 100% during the 60 min treatment, whereas the removal efficiency for PSf-HF fragments gradually decreased. However, PSf hemodialyzer in adsorptive filtration systems removed Aßs comparably or more than HexDC. Aß influx into the blood increases time-dependently. Concomitant use of HexDC and PSf hemodialyzer evoked a larger Aß1-40 influx than that of PSf hemodialyzer alone. However, Aß1-42 influx by PSf hemodialyzer alone was similar to or a little larger than influx by the combined system. Both systems evoked almost doubled Aß influx than estimated Aßs existing in the normal brain during the 4 h treatment. CONCLUSION: PSf hemodialyzer alone for a longer period and concomitant use of HexDC and PSf hemodialyzer for a shorter time effectively evoked a larger Aß influx. To evoke Aß1-42 influx, PSf hemodialyzer alone was effective enough. These findings of devices and treatment time may lead to optimal clinical settings for therapy and prevention of Alzheimer's disease.

Effects of Prolonging Eccentric Phase Duration in Parallel Back-Squat Training to Momentary Failure on Muscle Cross-Sectional Area, Squat One Repetition Maximum, and Performance Tests in University Soccer Players.

ABSTRACT: Shibata, K, Takizawa, K, Nosaka, K, and Mizuno, M. Effects of prolonging eccentric phase duration in parallel back-squat training to momentary failure on muscle cross sectional area, squat one repetition maximum, and performance tests in university soccer players. J Strength Cond Res 35(3): 668-674, 2021-This study aimed to compare 2 squat training programs repeated until momentary failure with different eccentric phase duration (2 seconds vs. 4 seconds) on the changes in muscle cross-sectional area, squat 1 repetition maximum (1RM), squat jump (SJ), and countermovement jump (CMJ) height, agility (T-test), and Yo-Yo intermittent recovery test (YY-IR2). Male university soccer players (19.9 ± 0.9 years, 172.2 ± 3.8 cm, 66.1 ± 6.6 kg) were randomly assigned to one of the 2 groups; CON for 2 seconds and ECC for 4 seconds (C2/E4, n = 11) or CON for 2 seconds and ECC for 2 seconds (C2/E2, n = 11). They performed parallel back-squat exercises twice a week for 6 weeks using 75% 1RM weight to momentary failure in each set for 3 sets with each protocol. Outcome measurements were taken before (Pre) and after 3 (Mid; 1RM, SJ, and CMJ only), and at 6 weeks (Post). One repetition maximum increased more (p < 0.05) for C2/E2 (Pre: 95.9 ± 12.2 kg, Mid: 108.2 ± 15.4 kg, Post: 113.6 ± 14.8 kg) than C2/E4 (95.5 ± 12.9 kg, 102.7 ± 15.6 kg, 105.5 ± 14.9 kg, respectively). Cross-sectional area (50% of the thigh length: 3.5 ± 2.8%), SJ (6.7 ± 8.9%) and CMJ height (6.3 ± 8.6%) increased similarly between C2/E2 and C2/E4, but no significant changes in T-test or YY-IR2 were evident in either group. These results suggest that increasing the ECC phase duration during squat exercises does not produce greater training effects when compared with a shorter ECC phase-duration program with momentary failure.

Comparison Between Two Volume-Matched Squat Exercises With and Without Momentary Failure for Changes in Hormones, Maximal Voluntary Isometric Contraction Strength, and Perceived Muscle Soreness.

ABSTRACT: Shibata, K, Takizawa, K, Tomabechi, N, Nosaka, K, and Mizuno, M. Comparison between two volume-matched squat exercises with and without momentary failure for changes in hormones, maximal voluntary isometric contraction strength and perceived muscle soreness. J Strength Cond Res 35(11): 3063-3068, 2021-The present study compared 2 squat exercises with and without momentary failure (MF) for changes in blood hormones, maximal voluntary isometric contraction (MVC) strength, and perceived muscle soreness (SOR). Ten physically active male students performed squat exercises at 75% of their 1 repetition maximum in 2 conditions. First, they performed each set to MF for 3 sets, and 2 weeks later, performed the same number of repetitions in 6 sets without MF (NMF). The rate of perceived exertion was assessed at 30 minutes after exercise. Blood lactate, serum concentrations of growth hormone (GH), testosterone, insulin-like growth factor 1 (IGF-1) and cortisol, MVC strength, and SOR were measured before and after each exercise. Rate of perceived exertion was higher (p < 0.01) in MF (8.3 ± 1.2) than in NMF (4.1 ± 1.4). Blood lactate was greater (p < 0.01) at 5 minutes after MF (7.2 ± 0.7 mM·L-1) than NMF (3.6 ± 0.7 mM·L-1). At 30 minutes after exercise, GH (MF: 12.3 ± 8.3 ng·ml-1, NMF: 4.4 ± 5.2 ng·ml-1) and cortisol (MF: 19.0 ± 4.3 µg·dl-1, NMF: 14.2 ± 4.6 µg·dl-1) were greater (p < 0.01) for MF than NMF, but no significant differences were observed between conditions for testosterone and IGF-1. Maximal voluntary isometric contraction strength decrease (6.1 ± 8.8%) at 24 hours after exercise was evident only for MF, but SOR at 24 hours after exercise was similar between MF (4.8 ± 3.3 cm) and NMF (2.5 ± 2.4 cm) conditions. These results suggest that mechanical and metabolic stimulus to the muscles were greater for MF than NMF condition.

Influx of Tau and Amyloid-ß Proteins into the Blood During Hemodialysis as a Therapeutic Extracorporeal Blood Amyloid-ß Removal System for Alzheimer's Disease.

The accumulation of amyloid-ß protein (Aß) and tau in the brain is a major pathological change related to Alzheimer's disease. We have continued to develop Extracorporeal Blood Aß Removal Systems (E-BARS) as a method for enhancing Aß clearance from the brain. Our previous report revealed that dialyzers effectively remove blood Aß and evoke large Aß influxes into the blood, resulting in a decrease in brain Aß accumulation after initiating hemodialysis, and that patients who underwent hemodialysis had lower brain Aß accumulation than those who did not. Here, plasma total tau concentrations from 30 patients undergoing hemodialysis were measured using an ultrasensitive immunoassay and compared to those from 11 age-matched controls. Plasma total tau concentrations were higher in patients with renal failure regardless of whether they underwent hemodialysis, suggesting the involvement of the kidneys in tau degradation and excretion. Hemodialyzers effectively removed blood Aß but not extracorporeal blood tau. The influx of tau into the blood was observed at around the 1 h period during hemodialysis sessions. However, the influx amount of tau was far smaller than that of Aß. Furthermore, histopathological analysis revealed similar, not significantly less, cerebral cortex phosphorylated tau accumulation between the 17 patients who underwent hemodialysis and the 16 age-matched subjects who did not, although both groups showed sparse accumulation. These findings suggest that hemodialysis may induce both tau and Aß migration into the blood. However, as a therapeutic strategy for Alzheimer's disease, it may only be effective for removing Aß from the brain.

Competitive achievement may be predicted by executive functions in junior tennis players: An 18-month follow-up study.

This study evaluates whether high levels of executive function predict competition results 18 months later in junior tennis players. Forty junior tennis players (20 girls, 20 boys; 9-15 years old) who regularly participate in prefecture tennis tournaments were recruited. All participants underwent executive function evaluations (the Design Fluency Task) in July 2015 and their prefecture junior rankings in August 2015 and February 2017 were recorded. As a result, after controlling for age and gender, the future ranking (February 2017) was significantly predicted by performance in the Design Fluency Task (ß = -.30, p = .02; ΔR2 = .08), whereas the prediction for August 2015 rank as the baseline was not significant (ß = -.19, p = .17; ΔR2 = .03). After controlling for age, gender, and ranking in the baseline, the change in ranking was significantly predicted by performance in the Design Fluency Task (ß = -.14, p = .02; ΔR2 = .02). This suggests that childhood executive function may play a significant role in success later in life. This study highlights how executive function predicts future success in a specific sport; as such, supporting the development of executive function may contribute to higher competition results.

Effects of 3-Week Work-Matched High-Intensity Intermittent Cycling Training with Different Cadences on VO2max in University Athletes.

The aim of this study is to clarify the effects of 3-week work-matched high-intensity intermittent cycling training (HIICT) with different cadences on the VO2max of university athletes. Eighteen university athletes performed HIICT with either 60 rpm (n = 9) or 120 rpm (n = 9). The HIICT consisted of eight sets of 20 s exercise with a 10 s passive rest between each set. The initial training intensity was set at 135% of VO2max and was decreased by 5% every two sets. Athletes in both groups performed nine sessions of HIICT during a 3-week period. The total workload and achievement rate of the workload calculated before experiments in each group were used for analysis. VO2max was measured pre- and post-training. After 3 weeks of training, no significant differences in the total workload and the achievement rate of the workload were found between the two groups. VO2max similarly increased in both groups from pre- to post-training (p = 0.016), with no significant differences between the groups (p = 0.680). These results suggest that cadence during HIICT is not a training variable affecting the effect of VO2max.

Effects of tennis play on executive function in 6-11-year-old children: a 12-month longitudinal study.

The present study aimed to assess the effects of 12 months of frequent tennis play on executive functions and the relationships of daily moderate-to-vigorous physical activity (MVPA), physical competence, and enjoyment of playing tennis to executive functions in children. Thirty-two children (6-11 years old) who had regularly played tennis (once a week; mean = 3 years, range = 0-6 years) before the study were enrolled in a 12-month intervention. Participants were allocated into two groups: low-dose (maintain current frequency of tennis play, N = 19) or high-dose (increased frequency of tennis play to four times per week, N = 13). Participants' MVPA, physical competence, enjoyment of playing tennis, and executive functions (i.e. inhibitory control, working memory, and cognitive flexibility) were evaluated before and after this intervention. The high-dose group demonstrated a greater improvement in working memory than the low-dose group, while there was no group difference in MVPA, physical competence, and enjoyment of playing tennis. Changes in MVPA were associated with improvements in cognitive flexibility. Changes in physical competence were associated with improvements in working memory and cognitive flexibility. Changes in the enjoyment of playing tennis were associated with improvements in inhibitory control. The current findings suggest that replacement of MVPA with sports activity, such as tennis enhances executive functions development, and suggest that sports programmes that seek to build competence and enjoyment might help support the development of executive functions in children.

Relationship between attention shifting and tennis performance during singles matches.

BACKGROUND: Cognitive ability, such as attention shifting, during tennis matches may be associated with players' performance through physical ability, technique, and exercise intensity. However, examinations of the relationship between attention shifting and performance in sport are limited to laboratory settings. The present study examined the relationships between exercise intensity, attention shifting, and tennis performance in singles tennis matches involving university tennis players using a field-based approach. METHODS: Sixteen university tennis players participated. Participants were evaluated concerning their attention shifting using a local-global task before a singles tennis match (pre-test: 0 minutes), during the match (inter-test: 30 minutes), and after the match (post-test: 60 minutes). Exercise intensity was evaluated using a heart rate monitor and ratings of perceived exertion. RESULTS: Higher ratings of perceived exertion and longer duration of vigorous physical activity were correlated with lower attention shifting at the inter-test period. Higher attention shifting at inter-test was related to greater tennis performance. CONCLUSIONS: The present study suggests that greater attention shifting during a singles tennis match may be related to higher quality tennis performance, and higher exercise intensity and perceived exertion may be associated with impairment of attention shifting during a match. Strategies for maintaining attention shifting during high-intensity physical activity in a tennis singles match may contribute to improved tennis performance.

Relationship between sports experience and executive function in 6-12-year-old children: independence from physical fitness and moderation by gender.

The purpose of this study was to evaluate the relationship between sports experience (i.e., tennis experience) and executive function in children while controlling for physical activity and physical fitness. Sixty-eight participants (6-12 years old, 34 males and 34 females) were enrolled in regular tennis lessons (mean = 2.4 years, range = 0.1-7.3 years) prior to the study. Executive functions, including inhibitory control (the Stroop Color-Word Test), working memory (the 2-back Task), and cognitive flexibility (the Local-global Task) were evaluated. Participants' levels of daily physical activity, ranging from moderate to vigorous, were evaluated using triaxial accelerometers. The total score for physical fitness was assessed using the Tennis Field Test. Hierarchical multiple regression analyses revealed interaction effects between gender and tennis experience on participants' reaction time (RT) on the switch cost of the Local-global Task after controlling for age, BMI, gender, physical activity, physical fitness, and tennis experience. Longer tennis experience was associated with shorter switch cost in males but not in females. Higher scores on physical fitness were positively associated with lower interference scores on the Stroop Color-Word Test, RT on the 2-back Task, and RT in the switching condition of the Local-global Task, after controlling for age, BMI, gender, and physical activity. In conclusion, all three foundational components of executive function (i.e., inhibitory control, working memory, and cognitive flexibility) were more strongly related to physical fitness than to physical activity in males and females, whereas greater cognitive flexibility was related to tennis experience only in the males.

Relationship of tennis play to executive function in children and adolescents.

This study evaluated the association between the frequency of tennis play and executive function in children and adolescents. One hundred and six junior tennis players (6-15 years old) participated in this study. Executive function, including inhibitory control, working memory, and cognitive flexibility were evaluated at rest. Females showed better inhibitory control and cognitive flexibility than males. In males, more frequent tennis play was associated with higher basic processing speed and inhibitory control after controlling for age, gender, body mass index (BMI), and tennis experience. More frequent tennis play was associated with better working memory in both males and females after controlling for age, gender, BMI, and tennis experience. Furthermore, longer tennis experience was related to better cognitive flexibility in males after controlling for age, gender, BMI, and frequency of tennis play. These findings suggest that tennis play is associated with the development of three foundational aspects of executive function (i.e. inhibitory control, working memory, cognitive flexibility). Especially, frequent participation in tennis play is related to better inhibitory control and working memory, while longer experience of tennis play is associated with better cognitive flexibility. Although development of inhibitory control and cognitive flexibility is slower in males than in females, the associations between tennis play and inhibitory control and cognitive flexibility appear to be larger in males than in females.

The beneficial effects of game-based exercise using age-appropriate tennis lessons on the executive functions of 6-12-year-old children.

This study evaluated the effects of two different types of tennis lessons-those involving a technique-based approach (TBA) and those involving a game-based approach (PLAY+STAY [P+S])-on the executive functions (EFs) of junior tennis players. Eighty-one tennis players (6-12 years old) were recruited and assigned to one of three groups: TBA, P+S, or watching TV (CONT). Subjects completed evaluations of EFs (inhibitory control, working memory, and cognitive flexibility) before and after 50min programs. The overall score for EFs improved significantly for both the P+S and TBA groups but not for the CONT group; indeed the CONT group showed no improvement in overall EFs. Furthermore, the overall EF score improved more for P+S participants than for those in TBA. Looking at components of EFs, the pattern for inhibitory control reflected the pattern for the overall EF index: Improvement in the P+S and TBA groups but not in the CONT group. Only the P+S group improved in working memory. Thus, playing tennis and practicing isolated tennis skills both improved EFs of junior players more than did watching TV, and game-based tennis lessons seem to hold more promise for improving EFs than drills of tennis skills.

Improved executive functions in 6-12-year-old children following cognitively engaging tennis lessons.

The aim of this cross-sectional study was to evaluate the relationships between cognitively engaging exercise (i.e., game-based and coordination exercises), executive functions (i.e., inhibitory control and working memory), and physical fitness. Forty junior tennis players (6-12 years old), who regularly participated in tennis lessons (2.55 years, SD = 1.61) prior to the study, were investigated. All participants completed evaluations of executive functions (inhibitory control and working memory) at rest. The duration of each lessons' instructional activities, including coordination training, game-based exercise, rallying, and non-physical activity (explanations and breaks), was recorded. Physical fitness was evaluated using the Tennis Field Test. A longer duration of game-based exercise was positively correlated with inhibitory control and physical fitness. Coordination training was associated with improved working memory. Non-physical activity was inversely correlated with inhibitory control, working memory, and physical fitness. The results suggest that game-based tennis lessons have beneficial effects on inhibitory control and physical fitness levels, and a longer duration of coordination training is associated with better working memory. The present study indicates that shortened non-physical activity time within a sports setting is associated with the development of executive functions and physical fitness.

Protein-containing nutrient supplementation following strength training enhances the effect on muscle mass, strength, and bone formation in postmenopausal women.

We evaluated the response of various muscle and bone adaptation parameters with 24 wk of strength training in healthy, early postmenopausal women when a nutrient supplement (protein, carbohydrate, calcium, and vitamin D) or a placebo supplement (a minimum of energy) was ingested immediately following each training session. At inclusion, each woman was randomly and double-blindedly assigned to a nutrient group or a placebo (control) group. Muscle hypertrophy was evaluated from biopsies, MRI, and dual-energy X-ray absorptiometry (DEXA) scans, and muscle strength was determined in a dynamometer. Bone mineral density (BMD) was measured using DEXA scans, and bone turnover was determined from serum osteocalcin and collagen type I cross-linked carboxyl terminal peptide. The nutrient group improved concentric and isokinetic (60 degrees /s) muscle strength from 6 to 24 wk by 9 +/- 3% (P < 0.01), whereas controls showed no change (1 +/- 2%, P > 0.05). Only the nutrient group improved lean body mass (P < 0.05) over the 24 wk. BMD responded similarly at the lumbar spine but changed differently in the two groups at the femoral neck (P < 0.05) [control: 0.943 +/- 0.028 to 0.930 +/- 0.024 g/mm(3) (-1.0 +/- 1.4%); nutrient group: 0.953 +/- 0.051 to 0.978 +/- 0.043 g/mm(3) (3.8 +/- 3.4%)] when adjusted for age, body mass index, and BMD at inclusion. Bone formation displayed an interaction (P < 0.05), mainly caused by increased osteocalcin at 24 wk in the nutrient group. In conclusion, we report that nutrient supplementation results in superior improvements in muscle mass, muscle strength, femoral neck BMD, and bone formation during 24 wk of strength training. The observed differences following such a short intervention emphasize the significance of postexercise nutrient supply on musculoskeletal maintenance.

Skeletal muscle adaptations to prolonged exposure to extreme altitude: a role of physical activity?

This study investigated skeletal muscle adaptations to high altitude and a possible role of physical activity levels. Biopsies were obtained from the m. quadriceps femoris (vastus) and m. biceps brachii (biceps) in 15 male subjects, 7 active and 8 less active. Samples were obtained at sea level and after 75 days altitude exposure at 5250 m or higher. The muscle fiber size decreased at an average of 15% in the vastus and biceps, respectively, and to the same extent in both groups. In both muscles, the mean number of capillaries was 2.1-2.2 cap.fiber(-1) before and after the exposure. As mean fiber area was reduced, the mean number of capillaries per unit area increased in all subjects (from 320 to 405 cap/mm2) with no difference between the active and less active groups. The two enzymes selected to reflect mitochondrial capacity, citrate synthase (CS) and 3-hydroxyl-CoA-dehydrogenase (HAD), did not change in the leg muscles with altitude exposure, CS: 28.7 (20.7-37.8) vs. 27.8 (23.8-29.4); HAD: 35.2 (20.3-43.1) vs. 30.6 (20.7-39.7) micromol.min(-1).g(-1) d.w, pre- and post-altitude, respectively. The muscle buffer capacity was elevated in both the vastus; 220 (194-240) vs. 232 (200-277) and the biceps muscles; 233 (190-301) vs. 253 (193-320) after the acclimatization period. In conclusion, mean fiber area was reduced in response to altitude exposure regardless of physical activity which in turn meant that with an unaltered capillary to fiber ratio there was an elevation in capillaries per unit of muscle area. Muscle enzyme activity was unaffected with altitude exposure in both groups, whereas muscle buffer capacity was increased.

Postexercise nutrient intake enhances leg protein balance in early postmenopausal women.

BACKGROUND: We investigated the effect of nutrient administration after a session of resistance exercise on muscle protein kinetics in six healthy, early postmenopausal women, in a crossover design of random and double-blinded administration of protein and carbohydrate (PC) or placebo (NON). METHODS: Fasted participants received a primed-constant infusion of L-[ring-2H5]-phenylalanine. After 90 minutes of rest, the participants performed leg-resistance exercises followed by the oral supplementation. During the following 4 hours, net protein balance (NB) and rate of disappearance and appearance of phenylalanine were calculated from arterial-venous blood samples and blood flow measurements. RESULTS: NB was elevated (p <.001) in the PC group compared to the NON group, and NB was not different from zero in the PC group, whereas it was negative in the NON group. Net balance results were supported by kinetic data from a reduced number of participants, showing that rate of disappearance was responsible for the initial (<1 hour) effect of PC, whereas a reduced rate of appearance enhanced the NB from 1.5 to 3 hours after training in the PC group. CONCLUSION: In early postmenopausal women, nutrient ingestion following resistance exercise improved anabolism by enhancing NB in skeletal muscle.

Association between regional quadriceps oxygenation and blood oxygen saturation during normoxic one-legged dynamic knee extension.

It is not clear whether muscle oxygenation (O(2-NIRS)) measured by near-infrared spectroscopy (NIRS) correlates with femoral venous SO2 (S(fv)o2) during normoxic exercise. Therefore, the purpose of this study was to compare physiologically calibrated O(2-NIRS) with S(fv)o2 in subjects performing one-legged dynamic knee extension exercise (1L-KEE). Five healthy male subjects (age 25+/-2 year, height 177.8+/-4.8 cm, body weight 67.1 +/- 5.0 kg; mean +/- SD) performed 1L-KEE at 20, 40, and 60% of peak work rate (WR-peak) each for 4 min. S(fv)o2 was measured at rest and during the 3rd minute of each work rate. O(2-NIRS) was continuously monitored in a proximal region of the vastus lateralis (VL-p), a distal region of VL (VL-d), and a proximal region of the rectus femoris (RF-p). S(fv)o2 was 56.0% at rest and decreased to 36.6 at 20% WR-peak, 35.8 at 40% WR-peak, and 31.1 at 60% WR-peak. There was a significant correlation between O(2-NIRS) and S(fv)o2(VL-p: r (2) = 0.62, VL-d: r2 = 0.35, RF-p: r2 = 0.62, with a moderate variation among individuals at each site; residual values = 4.83 - 11.75). These data indicate that NIRS measurement provides a reflection of S(fv)o2 during 20-60% WR-peak of normoxic 1L-KEE.

ATP economy of force maintenance in human tibialis anterior muscle.

PURPOSE: The aim of this study was investigate ATP economy of force maintenance in the human tibialis anterior muscle during 60 s of anaerobic voluntary contraction at 50% of maximum voluntary contraction (MVC). METHODS: ATP turnover rate was evaluated using P magnetic resonance spectroscopy (P-MRS). The total volume of ankle dorsiflexor muscles was assessed by H magnetic resonance imaging (MRI) (H-MRI), and the fiber type composition of the tibialis anterior muscle was evaluated using histochemical analysis of muscle biopsies. RESULTS: The tibialis anterior muscle occupied 59.7 +/- 0.6% (mean +/- SEM) of the total ankle dorsiflexor muscle volume, which was 267 +/- 10 cm. Relative cross-sectional areas occupied by Type I, IIA, and IIB fibers in the tibialis anterior were 69.3 +/- 2.2, 27.4 +/- 2.76, and 3.2 +/- 1.0%, respectively. ATP economy of force maintenance did not change significantly during the 60-s contraction. It averaged at 4.81 +/- 0.42 N.s.micromol-1, and correlated with the relative cross-sectional area of the muscle occupied by Type I fiber (r = 0.73, P < 0.01). For the second half of the contraction, subjects dropping in force showed lower ATP economy compared with those maintaining the force (3.7 +/- 0.6 vs 5.3 +/- 0.6 N.s.micromol-1; P < 0.05). CONCLUSION: It is argued that the unchanged ATP economy of force maintenance during the voluntary contraction could be due to an increase in the ATP economy of contracting muscle fibers offsetting the effects of increased temperature and low ATP economy of Type II fibers. Mechanical interaction between motor units could also act to improve ATP economy of force maintenance.