Responses of Angiogenic Regulators to Resistance Exercise Under Systemic Hypoxia.

ABSTRACT: Kon, M, Ikeda, T, Homma, T, and Suzuki, Y. Responses of angiogenic regulators to resistance exercise under systemic hypoxia. J Strength Cond Res 35(2): 436-441, 2021-Resistance exercise and hypoxia powerfully affect the secretions of angiogenic regulators. However, the effects of resistance exercise under acute systemic hypoxia on circulating levels of angiogenic regulators are unknown. Therefore, we investigated the effects of resistance exercise under systemic hypoxia on angiogenic regulator responses. Twelve healthy male subjects completed 2 experimental trials: (a) resistance exercise under normoxia (NRE), and (b) resistance exercise under systemic hypoxia (13% oxygen) (HRE) using a hypoxic generator. The subjects performed 2 consecutive resistance exercises (bench press and bilateral leg press), consisting of 5 sets with 10 repetitions at 70% of 1 repetition maximum with a 1-minute rest between sets. Serum vascular endothelial growth factor (VEGF), matrix metalloproteinase (MMP)-2, MMP-9, and endostatin concentrations were measured before exercise (and before exposure to hypoxia in the HRE trial) and at 0, 15, and 30 minutes after the resistance exercises. In both trials, serum VEGF, MMP-2, MMP-9, and endostatin concentrations significantly increased after the exercises compared with preexercise values (p < 0.05). At 0 minutes after exercise, the percentage change in VEGF concentration was significantly higher in the HRE trial compared with that in the NRE trial (p < 0.05). However, the exercise-induced changes in MMP-2, MMP-9, and endostatin concentrations did not differ between trials. The present results demonstrate that acute systemic hypoxia induces a greater resistance exercise-induced VEGF response, suggesting that hypoxia plays an important role in increasing the VEGF response to a bout of resistance exercise.

Anti-melanogenic activity of salacinol by inhibition of tyrosinase oligosaccharide processing.

Hyperpigmentation that manifests through melasma and solar lentigo (age spots), although mostly harmless for health, bothers many people. Controlling the rate-limiting activity of tyrosinase is most effective for suppressing excessive melanin formation and accordingly recent research has focused on the maturation of tyrosinase. Salacia, a medicinal plant, has been used to treat diabetes in India and Sri Lanka. Salacia extract reportedly contains components that inhibit the activity of α-glucosidase. Salacinol, the active ingredient in Salacia extract, has unique thiosugar sulphonium sulphate inner salt structure. Here, we observed that the salacinol component of Salacia extract possesses anti-melanogenic activity in comparison to various existing whitening agents. Although the anti-melanogenic mechanism of salacinol is presumably medicated by inhibition of tyrosinase activity, which is often found in existing whitening agents, salacinol did not inhibit tyrosinase activity in vitro. Analysis of the intracellular state of tyrosinase showed a decrease in the mature tyrosinase form due to inhibition of N-linked oligosaccharide processing. Salacinol inhibited the processing glucosidase I/II, which are involved in the initial stage of N-linked glycosylation. Owing to high activity, low cytotoxicity and high hydrophilicity, salacinol is a promising candidate compound in whitening agents aimed for external application on skin.

Applicability of Supraclavicular Oxygenated and Total Hemoglobin Evaluated by Near-Infrared Time-Resolved Spectroscopy as Indicators of Brown Adipose Tissue Density in Humans.

Brown adipose tissue (BAT) may potentially be used in strategies for preventing lifestyle-related diseases. We examine evidence that near-infrared time-resolved spectroscopy (NIRTRS) is capable of estimating human BAT density (BAT-d). The parameters examined in this study are total hemoglobin [total-Hb]sup, oxygenated Hb [oxy-Hb]sup, deoxygenated Hb [deoxy-Hb]sup, Hb O2 saturation (StO2sup), and the reduced scattering coefficient in the supraclavicular region (µs'sup), where BAT deposits can be located; corresponding parameters in the control deltoid region are obtained as controls. Among the NIRTRS parameters, [total-Hb]sup and [oxy-Hb]sup show region-specific increases in winter, compared to summer. Further, [total-Hb]sup and [oxy-Hb]sup are correlated with cold-induced thermogenesis in the supraclavicular region. We conclude that NIRTRS-determined [total-Hb]sup and [oxy-Hb]sup are useful parameters for evaluating BAT-d in a simple, rapid, non-invasive manner.

Gene expression profile of muscle adaptation to high-intensity intermittent exercise training in young men.

High-intensity intermittent exercise training (HIIT) has been proposed as an effective approach for improving both, the aerobic and anaerobic exercise capacity. However, the detailed molecular response of the skeletal muscle to HIIT remains unknown. We examined the effects of the HIIT on the global gene expression in the human skeletal muscle. Eleven young healthy men participated in the study and completed a 6-week HIIT program involving exhaustive 6-7 sets of 20-s cycling periods with 10-s rests. In addition to determining the maximal oxygen uptake ([Formula: see text]), maximal accumulated oxygen deficit, and thigh muscle cross-sectional area (CSA), muscle biopsy samples were obtained from the vastus lateralis before and after the training to analyse the skeletal muscle transcriptome. The HIIT program significantly increased the [Formula: see text], maximal accumulated oxygen deficit, and thigh muscle CSA. The expression of 79 genes was significantly elevated (fold-change >1.2), and that of 73 genes was significantly reduced (fold-change <0.8) after HIIT. Gene ontology analysis of the up-regulated genes revealed that the significantly enriched categories were "glucose metabolism", "extracellular matrix", "angiogenesis", and "mitochondrial membrane". By providing information about a set of genes in the human skeletal muscle that responds to the HIIT, the study provided insight into the mechanism of skeletal muscle adaptation to HIIT.

Brown adipose tissue density measured by near-infrared time-resolved spectroscopy in Japanese, across a wide age range.

F18-fluorodeoxyglucose (FDG)-positron emission tomography (PET) along with computed tomography (CT) is a standard method for assessing brown adipose tissue (BAT) activity. We tested the usefulness of near-infrared time-resolved spectroscopy (NIRTRS) as a simple and noninvasive method for evaluating BAT density (BAT-d) by examining the effects of some factors known to influence BAT activity. The total hemoglobin concentration as a parameter of BAT-d was evaluated using NIRTRS in the supraclavicular region in 413 Japanese individuals. The associations were analyzed between BAT-d and sex, age, the percentages of body fat (%BF), visceral fat (VF), and the seasonal ambient temperature (AmT) fluctuations. Age was associated with decreased BAT-d (P < 0.05). There was no sex difference in the BAT-d, except for those in their twenties. Multivariate analyses revealed that %BF and VF were correlated with BAT-d, and the lower AmT (around 4°C or 5°C) for 4 and 6 weeks prior to the measurement day was associated with an increase in the BAT-d. Our NIRTRS results were analogous to those reported with FDG18-PET / CT, indicating the usefulness of NIRTRS. BAT-d might increase during the 4 and 6 weeks after the AmT decreases to lower than 4°C or 5°C.

Melanosome degradation in epidermal keratinocytes related to lysosomal protease cathepsin V.

The cause of hyperpigmentation, such as solar lentigo and seborrheic keratosis, is the excessive accumulation of melanin pigments in the epidermal basal layer. Melanin pigments are synthesized in the melanosomes, which are specific organelles produced by melanocytes in the basal layer. Melanosomes containing melanin pigments are transported to the neighboring keratinocytes. However, the behavior of melanosomes after being transported to the keratinocytes has been poorly understood. In this study, we focused on a lysosomal protease cathepsin V (CTSV) to clarify the mechanism underlying melanosome degradation in the keratinocytes. Using immunohistochemical observation, we found that CTSV was highly expressed across the entire epidermis in normal skin; however, CTSV expression levels were lower in the basal layer than those in the stratum corneum side in the hyperpigmented region. Moreover, we found that melanosome degradation was suppressed in CTSV knockdown cells. These results indicated that CTSV is involved in melanosome degradation.

Seasonal differences in brown adipose tissue density and pulse rate variability in a thermoneutral environment.

BACKGROUND: Brown adipose tissue (BAT) is sympathetically activated and induces thermogenesis during cold exposure, thereby influencing energy expenditure and body fat levels. The very low frequency (VLF) components of pulse rate variability could be a form of thermogenic sympathetic nervous activity, but no clear relationship has yet been reported between VLF activity and BAT density. We therefore aimed to evaluate the association between them. METHODS: We enrolled 20 adults in winter and 20 matched adults in summer. We assessed BAT densities based on total hemoglobin concentrations ([total-Hb]) measured with near-infrared time-resolved spectroscopy. We calculated VLF activity from pulse rate variability measurements. RESULTS: BAT density ([total-Hb]; winter 70.5 ± 17.0 µM, summer 57.8 ± 18.3 µM) and VLF activity (winter 6.7 ± 0.8, summer 6.1 ± 0.9) were significantly higher in winter than in summer (P < 0.05). However, there was no significant correlation between VLF activity and BAT density in either season. CONCLUSION: Each parameter exhibited seasonal variation, but we failed to observe any significant correlations.

Daily ingestion of catechin-rich beverage increases brown adipose tissue density and decreases extramyocellular lipids in healthy young women.

PURPOSE: Brown adipose tissue (BAT) contributes to the regulation of non-shivering thermogenesis and adiposity. Increasing BAT has recently attracted much attention as a countermeasure to obesity. Animal studies have shown that prolonged catechin treatment increases uncoupling protein 1, a thermogenic protein in BAT. On the other hand, supportable evidence in human is lacking. Thus, the purpose of this study was to examine whether BAT increases after catechin ingestion in humans. METHODS: Twenty-two healthy young women were given either a catechin-rich (540 mg/day; catechin) or placebo beverage every day for 12 weeks in a double-blind design. BAT density was measured using near-infrared time-resolved spectroscopy (NIRTRS), visceral fat area were measured using magnetic resonance imaging, extramyocellular lipids (EMCL) using proton magnetic resonance spectroscopy, and body fat mass using dual-energy X-ray absorptiometry scans. RESULTS: BAT density was significantly increased (18.8 %), and EMCL was decreased (17.4 %) after the 12-week ingestion. There was a significant negative correlation between the changes in BAT density and those in EMCL (r = -0.66, P < 0.05). There were no notable changes in other parameters. CONCLUSIONS: In conclusion, prolonged ingestion of a catechin-rich beverage increases the BAT density in parallel with a decrease in EMCL.

New ultrasonography-based method for predicting total skeletal muscle mass in male athletes.

[Purpose] This study aimed 1) to assess whether a prediction model for whole body skeletal muscle mass that is based on a sedentary population is applicable to young male athletes, and 2) to develop a new skeletal muscle mass prediction model for young male athletes. [Subjects and Methods] The skeletal muscle mass of 61 male athletes was measured using magnetic resonance imaging (MRI) and estimated using a previous prediction model (Sanada et al., 2006) with B-mode ultrasonography. The prediction model was not suitable for young male athletes, as a significant difference was observed between the means of the estimated and MRI-measured skeletal muscle mass. Next, the same subjects were randomly assigned to a development or validation group, and a new model specifically relevant to young male athletes was developed based on MRI and ultrasound data obtained from the development group. [Results] A strong correlation was observed between the skeletal muscle mass estimated by the new model and the MRI-measured skeletal muscle mass (r=0.96) in the validation group, without significant difference between their means. No bias was found in the new model using Bland-Altman analysis (r=-0.25). [Conclusion] These results validate the new model and suggest that ultrasonography is a reliable method for measuring skeletal muscle mass in young male athletes.

Assessment of human brown adipose tissue density during daily ingestion of thermogenic capsinoids using near-infrared time-resolved spectroscopy.

18F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDGPET/CT) is widely used as a standard method for evaluating human brown adipose tissue (BAT), a recognized therapeutic target of obesity. However, a longitudinal BAT study using FDG-PET/CT is lacking owing to limitations of the method. Near-infrared time-resolved spectroscopy (NIR(TRS)) is a technique for evaluating human BAT density noninvasively. This study aimed to test whether NIRTRS could detect changes in BAT density during or after long-term intervention. First, using FDG-PET/CT, we confirmed a significant increase (+48.8%, P < 0.05) in BAT activity in the supraclavicular region after 6-week treatment with thermogenic capsaicin analogs, capsinoids. Next, 20 volunteers were administered either capsinoids or placebo daily for 8 weeks in a double-blind design, and BAT density was measured using NIR(TRS) every 2 weeks during the 8-week treatment period and an 8-week period after stopping treatment. Consistent with FDG-PET/CT results, NIR(TRS) successfully detected an increase in BAT density during the 8-week treatment (+46.4%, P < 0.05), and a decrease in the 8-week follow-up period (-12.5%, P = 0.07), only in the capsinoid-treated, but not the placebo, group. Thus, NIR(TRS) can be applied for quantitative assessment of BAT in longitudinal intervention studies in humans.

A single-dose of oral nattokinase potentiates thrombolysis and anti-coagulation profiles.

Our aim was to determine the quantitative effects of a single-dose of Nattokinase (NK) administration on coagulation/fibrinolysis parameters comprehensively in healthy male subjects. A double-blind, placebo-controlled cross-over NK intervention study was carried out in 12 healthy young males. Following the baseline blood draw, each subject was randomized to receive either a single-dose of 2,000 FU NK (NSK-SD, Japan Bio Science Laboratory Co., Ltd) or placebo with subsequent cross-over of the groups. Subjects donated blood samples at 2, 4, 6 and 8 hours following administration for analysis of coagulation/fibrinolysis parameters. As a result, D-dimer concentrations at 6, and 8 hours, and blood fibrin/fibrinogen degradation products at 4 hours after NK administration elevated significantly (p < 0.05, respectively). Factor VIII activity declined at 4 and 6 hours (p < 0.05, respectively), blood antithrombin concentration was higher at 2 and 4 hours (p < 0.05, respectively), and the activated partial thromboplastin time prolonged significantly at 2 and 4 hours following NK administration (p < 0.05 and p < 0.01, respectively). All the changes, however, were within the normal range. In conclusion, thus, a single-dose of NK administration appears enhancing fibrinolysis and anti-coagulation via several different pathways simultaneously.

Ischemic preconditioning accelerates muscle deoxygenation dynamics and enhances exercise endurance during the work-to-work test.

Ischemic preconditioning (IPC) improves maximal exercise performance. However, the potential mechanism(s) underlying the beneficial effects of IPC remain unknown. The dynamics of pulmonary oxygen uptake (VO2) and muscle deoxygenation during exercise is frequently used for assessing O2 supply and extraction. Thus, this study examined the effects of IPC on systemic and local O2 dynamics during the incremental step transitions from low- to moderate- and from moderate- to severe-intensity exercise. Fifteen healthy, male subjects were instructed to perform the work-to-work cycling exercise test, which was preceded by the control (no occlusion) or IPC (3 × 5 min, bilateral leg occlusion at >300 mmHg) treatments. The work-to-work test was performed by gradually increasing the exercise intensity as follows: low intensity at 30 W for 3 min, moderate intensity at 90% of the gas exchange threshold (GET) for 4 min, and severe intensity at 70% of the difference between the GET and VO2 peak until exhaustion. During the exercise test, the breath-by-breath pulmonary VO2 and near-infrared spectroscopy-derived muscle deoxygenation were continuously recorded. Exercise endurance during severe-intensity exercise was significantly enhanced by IPC. There were no significant differences in pulmonary VO2 dynamics between treatments. In contrast, muscle deoxygenation dynamics in the step transition from low- to moderate-intensity was significantly faster in IPC than in CON (27.2 ± 2.9 vs. 19.8 ± 0.9 sec, P < 0.05). The present findings showed that IPC accelerated muscle deoxygenation dynamics in moderate-intensity exercise and enhanced severe-intensity exercise endurance during work-to-work test. The IPC-induced effects may result from mitochondrial activation in skeletal muscle, as indicated by the accelerated O2 extraction.

Intramyocellular and Extramyocellular Lipids Are Associated With Arterial Stiffness.

BACKGROUND: Obese and overweight patients are at increased risk of arterial stiffness, and visceral, epicardial and hepatic fat accumulation is associated with cardiovascular disease risk. In general, muscular lipids are stored either in interstitial adipose tissue (extramyocellular lipid (EMCL)) or in lipid droplets within muscle cells (intramyocellular lipid (IMCL)). However, the association between IMCL or EMCL content and arterial stiffness remains unclear. This cross-sectional study aimed to clarify this association. METHODS: A total of 237 subjects (18-81 years) were enrolled in this study. The IMCL and EMCL contents of the right vastus lateralis muscle were evaluated by proton magnetic resonance spectroscopy. Arterial stiffness was estimated using brachial-ankle pulse wave velocity (baPWV). RESULTS: There were significant correlations between baPWV and the contents of both IMCL (R = -0.23, P < 0.001) and EMCL (R = 0.53, P < 0.001) in all subjects. The baPWV negatively correlated with IMCL content (R = -0.45, P < 0.001) in females only. In contrast, significant positive correlations were observed between baPWV and EMCL content in both males (R = 0.59, P < 0.001) and females (R = 0.55, P < 0.001). IMCL and EMCL contents contributed independently to baPWV variation after adjustment for age, sex, body mass index, visceral and subcutaneous abdominal fat, upper and lower limb fat, blood pressure, heart rate, and lipid profiles. CONCLUSION: These results suggest that IMCL and EMCL contents may be a risk factor for arterial stiffness, and this association differed with gender and age.

Once-weekly muscle endurance and strength training prevents deterioration of muscle oxidative function and attenuates the degree of strength decline during 3-week forearm immobilization.

PURPOSE: Muscle unloading causes muscle function deterioration, but the extent to which training frequency or volume can be reduced while preserving muscle function during muscle unloading is unknown. We examined the effects of low-volume muscle endurance and strength training on forearm muscle oxidative capacity, endurance, and strength during a 3-week immobilization. METHODS: Twenty-seven, healthy, male volunteers were divided into four groups: immobilization only (IMM); immobilization with endurance and strength training, once-weekly (IMM + EST1) or twice-weekly (IMM + EST2); and control, without immobilization or training (CNT). Endurance training involved dynamic handgrip exercise, at 30% of maximal voluntary contraction (MVC), until exhaustion (~60 s). Strength training involved intermittent isometric handgrip exercise at 70% MVC (40 s). Muscle oxidative capacity was evaluated after exercise using the phosphocreatine recovery time constant using (31)phosphorus magnetic resonance spectroscopy. Endurance performance was evaluated according to the total work during dynamic handgrip exercise at 30% MVC at 1 Hz until exhaustion. RESULTS: Muscle oxidative capacity and total work deterioration was restricted to the IMM (P < 0.05) group. MVC decreased in the IMM and IMM + EST1 (P < 0.05) groups. However, the MVC amplitude decrease in the IMM + EST1 group was smaller than that in the IMM (P < 0.05) group. MVC remained unchanged in the other groups. CONCLUSION: During the 3-week immobilization, twice-weekly low-volume muscle endurance and strength training prevented deterioration in muscle strength, oxidative capacity, and endurance performance. Moreover, once-weekly muscle endurance and strength training prevented the deterioration of muscle oxidative capacity and endurance performance, and attenuated the degree of muscle strength decline.

Effects of low-intensity resistance exercise under acute systemic hypoxia on hormonal responses.

Previous studies have shown that low-intensity resistance exercises with vascular occlusion and slow movement effectively increase muscular size and strength. Researchers have speculated that local hypoxia by occlusion and slow movement may contribute to such adaptations via promoting anabolic hormone secretions by the local accumulation of metabolites. In this study, we determined the effects of low-intensity resistance exercise under acute systemic hypoxia on metabolic and hormonal responses. Eight male subjects participated in 2 experimental trials: (a) low-intensity resistance exercise while breathing normoxic air (normoxic resistance exercise [NR]), (b) low-intensity resistance exercise while breathing 13% oxygen (hypoxic resistance exercise [HR]). The resistance exercises (bench press and leg press) consisted of 14 repetitions for 5 sets at 50% of maximum strength with 1 minute of rest between sets. Blood lactate (LA), serum growth hormone (GH), norepinephrine (NE), testosterone, and cortisol concentrations were measured before normoxia and hypoxia exposures; 15 minutes after the exposures; and at 0, 15, and 30 minutes after the exercises. The LA levels significantly increased after exercises in both trials (p ≤ 0.05). The area under the curve for LA after exercises was significantly higher in the HR trial than in the NR trial (p ≤ 0.05). The GH significantly increased only after the HR trial (p ≤ 0.05). The NE and testosterone significantly increased after the exercises in both trials (p ≤ 0.05). Cortisol did not significantly change in both trials. These results suggest that low-intensity resistance exercise in the hypoxic condition caused greater metabolic and hormonal responses than that in the normoxic condition. Coaches may consider low-intensity resistance exercise under systemic hypoxia as a potential training method for athletes who need to maintain muscle mass and strength during the long in-season.

Low-volume strength and endurance training prevent the decrease in exercise hyperemia induced by non-dominant forearm immobilization.

We examined the effect of 3-week upper limb immobilization on conduit artery cross-sectional area and peak hyperemia (BF(peak)) after exhaustive dynamic handgrip exercise (Ex(dyn)), and that of low-volume strength and endurance training during immobilization. Healthy volunteers (n = 21; mean age, 22 years) were divided into 3 groups: immobilization only (IMM; n = 7), immobilization with training (STR + END; n = 7), and control (no immobilization or training, CNT; n = 7). Endurance training comprised Ex(dyn) at 30% maximum voluntary contraction (MVC) (duration of each session, ~60 s; twice weekly). Strength training involved intermittent isometric handgrip exercise at 70% MVC (duration of each session, 40 s; twice weekly), repeated 10 times. We used ultrasound methods to measure the brachial artery cross-sectional area and the BF(peak) after Ex(dyn) for 5 min pre- and post-immobilization. We found a significant group by time interaction in BF(peak) (p < 0.05). A significant decrease was found in BF(peak) in the IMM (p < 0.05) between pre- and post-immobilization and a protective effect in the STR + END. The 3-week upper limb immobilization did not influence the baseline artery cross-sectional area. In conclusion, BF(peak) decreased after 3-week upper limb immobilization and a combination of strength training and endurance training preserved the blunted BF(peak).

Effects of acute hypoxia on metabolic and hormonal responses to resistance exercise.

INTRODUCTION: Several recent studies have shown that resistance exercise combined with vascular occlusion effectively causes increases in muscular size and strength. Researchers speculated that the vascular occlusion-induced local hypoxia may contribute to the adaptations via promoting anabolic hormone secretions stimulated by local accumulation of metabolic subproducts. Here, we examined whether acute systemic hypoxia affects metabolic and hormonal responses to resistance exercise. METHODS: Twelve male subjects participated in two experimental trials: 1) resistance exercise while breathing normoxic air [normoxic resistance exercise (NR)] and 2) resistance exercise while breathing 13% oxygen [hypoxic resistance exercise (HR)]. The resistance exercises (bench press and leg press) consisted of 10 repetitions for five sets at 70% of maximum strength with 1-min rest between sets. Blood lactate, serum growth hormone (GH), epinephrine (E), norepinephrine (NE), insulin-like growth factor 1, testosterone, and cortisol concentrations were measured before normoxia and hypoxia exposures, 15 min after the exposures, and at 0, 15, 30, and 60 min after the exercises. RESULTS: Lactate significantly increased after exercises in both trials (P < 0.05). In the HR trial, GH and cortisol significantly increased after the exercise (P < 0.05) but not in the NR trial. The E, NE, insulin-like growth factor 1, and testosterone significantly increased after the exercises in both trials (P < 0.05). The mean values of lactate, GH, E, and NE after exercises were significantly higher in the HR trial than those in the NR trial (P < 0.05). CONCLUSIONS: These findings suggest that resistance exercise in hypoxic condition caused greater accumulation of metabolites and strong anabolic hormone response.

Effects of cooling on human skin and skeletal muscle.

To investigate the effects of cooling on local temperature and circulation in the skin and skeletal muscle at different cooling temperatures. Ten male subjects (mean age 24.9 years) participated in this study. Intramuscular temperatures were measured by inserting two 22-gauge temperature probes (needle length; 8 and 18 mm) into the ankle dorsiflexors, while skin temperature was measured using a thermocouple attached to the leg skin anteriorly. Near-infrared spectroscopy was also used to evaluate the concentration changes in oxygenated, deoxygenated, and total hemoglobin/myoglobin in local skin and skeletal muscle. These measurements were simultaneously performed during the 10-min noncooling, 30-min cooling (cooling pad temperature; 0, 10, or 20 degrees C), and 60-min recovery periods. Under all cooling conditions, skin and intramuscular temperatures decreased during cooling (P < 0.01) and began to increase after the cooling pad was removed. However, these values did not return to baseline values during the recovery period (P < 0.01). Moreover, tissue temperatures tended to show lower values during cooling at lower cooling temperatures. All hemoglobin/myoglobin concentrations also showed a concomitant significant decrease during cooling under three cooling conditions (P < 0.01); the oxygenated and total hemoglobin/myoglobin concentrations did not return to the exact values before cooling during the recovery period. This study suggested that the rate of decrease in tissue temperature depends on the cooling temperature and the effects of cooling on tissue temperatures and circulation tend to be maintained during 60 min post-cooling period despite the cooling temperature.

Age and activity status affect muscle reoxygenation time after maximal cycling exercise.

PURPOSE: The purpose of this study was to determine the interaction of age and habitual physical activity on recovery time of muscle oxygenation following maximal cycling exercise (CycEXmax). METHODS: Twelve sedentary middle-aged (50+/-6), 13 sedentary elderly (66+/-3), 13 active middle-aged (53+/-5), and 20 active elderly (67+/-5) women participated in this study. We evaluated the peak pulmonary oxygen uptake (VO2peak) during CycEXmax and the half-recovery time of muscle oxygenation (T1/2reoxy time) using near-infrared spectroscopy at the vastus lateralis (VL) during the recovery phase after CycEXmax. RESULTS: T1/2reoxy time was significantly greater in the elderly subjects than in the middle-aged subjects in both sedentary (P<0.05) and active groups (P<0.01). T1/2reoxy time of the active group was lower (P<0.01) than that of the sedentary group regardless of age. Age was significantly correlated to T1/2reoxy time in both sedentary and active groups (in both sedentary and active groups: P<0.01). The slope of T1/2reoxy time against age in the sedentary group was significantly greater (VL: P<0.05) than that of the active group. VO2peak showed significant inverse correlation with T1/2reoxy time at the VL in both sedentary and active groups. The slope of VO2peak against T1/2reoxy time showed no significant differences between middle-aged and elderly subjects. CONCLUSION: The results of this study suggest that T1/2reoxy time was prolonged with aging, regardless of habitual physical activity levels. However, habitual physical activity may prevent the age-related prolongation in T1/2reoxy time after CycEXmax. VO2peak appears to be one of the major factors determining T1/2reoxy time, not age.

Muscle oxidative metabolism accelerates with mild acidosis during incremental intermittent isometric plantar flexion exercise.

BACKGROUND: It has been thought that intramuscular ADP and phosphocreatine (PCr) concentrations are important regulators of mitochondorial respiration. There is a threshold work rate or metabolic rate for cellular acidosis, and the decrease in muscle PCr is accelerated with drop in pH during incremental exercise. We tested the hypothesis that increase in muscle oxygen consumption (o2mus) is accelerated with rapid decrease in PCr (concomitant increase in ADP) in muscles with drop in pH occurs during incremental plantar flexion exercise. METHODS: Five male subjects performed a repetitive intermittent isometric plantar flexion exercise (6-s contraction/4-s relaxation). Exercise intensity was raised every 1 min by 10% maximal voluntary contraction (MVC), starting at 10% MVC until exhaustion. The measurement site was at the medial head of the gastrocnemius muscle. Changes in muscle PCr, inorganic phosphate (Pi), ADP, and pH were measured by 31P-magnetic resonance spectroscopy. o2mus was determined from the rate of decrease in oxygenated hemoglobin and/or myoglobin using near-infrared continuous wave spectroscopy under transient arterial occlusion. Electromyogram (EMG) was also recorded. Pulmonary oxygen uptake (o2pul ) was measured by the breath-by-breath gas analysis. RESULTS: EMG amplitude increased as exercise intensity progressed. In contrast, muscle PCr, ADP, o2mus, and o2pul did not change appreciably below 40% MVC, whereas above 40% MVC muscle PCr decreased, and ADP, o2mus, and o2pul increased as exercise intensity progressed, and above 70% MVC, changes in muscle PCr, ADP, o2mus, and o2pul accelerated with the decrease in muscle pH (~6.78). The kinetics of muscle PCr, ADP, o2mus, and o2pul were similar, and there was a close correlation between each pair of parameters (r = 0.969~0.983, p < 0.001). CONCLUSION: With decrease in pH muscle oxidative metabolism accelerated and changes in intramuscular PCr and ADP accelerated during incremental intermittent isometric plantar flexion exercise. These results suggest that rapid changes in muscle PCr and/or ADP with mild acidosis stimulate accelerative muscle oxidative metabolism.