The electromyographic (EMG) activity and force relationship, i.e. EMG-force relationship, is a valuable indicator of the degree of the neuromuscular activation during isometric force production. ...However, there is minimal information available regarding the EMG-force relationship of individual triceps brachii (TB) muscles at different elbow joint angles. This study aimed to compare the EMG-force relationships of the medial (TB-Med), lateral (TB-Lat), and long heads (TB-Long) of the TB. 7 men and 10 women performed force matching isometric tasks at 20%, 40%, 60%, and 80%maximum voluntary contraction (MVC) at 60°, 90°, and 120° of extension. During the submaximal force matching tasks, the surface EMG signals of the TB-Med, TB-Lat, and TB-Long were recorded and calculated the root mean square (RMS). RMS of each force level were then normalized by RMS at 100%MVC. For the TB-Med, ultrasonography was used to determine the superficial region of the muscle that faced the skin surface to minimize cross-talk. The joint angle was monitored using an electrogoniometer. The elbow extension force, elbow joint angle, and surface EMG signals were simultaneously sampled at 2 kHz and stored on a personal computer. The RMS did not significantly differ between the three muscles, except between the TB-Med and TB-Lat during 20%MVC at 60°. The RMS during force levels of greater than or equal to 60%MVC at 120° was significantly lower than that at 60° or 90° for each muscle. The sum of difference, which represents the difference in RMS from the identical line, did not significantly differ in any of the assessed muscles in the present study. This suggests that a relatively smaller neuromuscular activation could be required when the elbow joint angle was extended. However, neuromuscular activation levels and relative force levels were matched in all three TB synergists when the elbow joint angle was at 90° or a more flexed position.
Acute moderate intensity exercise has been shown to improve cognitive performance. In contrast, hypoxia is believed to impair cognitive performance. The detrimental effects of hypoxia on cognitive ...performance are primarily dependent on the severity and duration of exposure. In this review, we describe how acute exercise under hypoxia alters cognitive performance, and propose that the combined effects of acute exercise and hypoxia on cognitive performance are mainly determined by interaction among exercise intensity and duration, the severity of hypoxia, and duration of exposure to hypoxia. We discuss the physiological mechanism(s) of the interaction and suggest that alterations in neurotransmitter function, cerebral blood flow, and possibly cerebral metabolism are the primary candidates that determine cognitive performance when acute exercise is combined with hypoxia. Furthermore, acclimatization appears to counteract impaired cognitive performance during prolonged exposure to hypoxia although the precise physiological mechanism(s) responsible for this amelioration remain to be elucidated. This review has implications for sporting, occupational, and recreational activities at terrestrial high altitude where cognitive performance is essential. Further studies are required to understand physiological mechanisms that determine cognitive performance when acute exercise is performed in hypoxia.
New Findings
What is the central question of this study?
Increased work of breathing and the accumulation of metabolites have neural and cardiovascular consequences through a respiratory ...muscle‐induced metaboreflex. The influence of the respiratory muscle‐induced metaboreflex on splanchnic blood flow in humans remains unknown.
What is the main finding and its importance?
Coeliac artery blood flow decreased gradually during inspiratory resistive breathing, accompanied by a progressive increase in arterial blood pressure. It is possible that the respiratory muscle‐induced metaboreflex contributes to splanchnic blood flow regulation.
The purpose of this study was to clarify the effect of increasing inspiratory muscle work on coeliac artery blood flow. Eleven healthy young males completed the study. The subjects performed voluntary hyperventilation with or without inspiratory resistance (loading or non‐loading trial; tidal volume of 40% of vital capacity and breathing frequency of 20 breaths/min). The loading trial was conducted with inspiratory resistance (40% of maximal inspiratory pressure) and was terminated when the subjects could no longer maintain the target tidal volume or breathing frequency. The non‐loading trial was conducted without inspiratory resistance and was of the same duration as the loading trial. Arterial blood pressure was recorded using finger photoplethysmography, and coeliac artery blood flow was measured using Doppler ultrasound. Mean arterial blood pressure increased gradually during the loading trial (mean ± SD; from 89.0 ± 10.8 to 103.9 ± 17.3 mmHg) but not in the non‐loading trial (from 88.7 ± 5.9 to 90.4 ± 9.9 mmHg). Coeliac artery blood flow and coeliac vascular conductance decreased gradually during the loading trial (from 601.2 ± 155.7 to 482.6 ± 149.5 mL/min and from 6.9 ± 2.2 to 4.8 ± 1.7 mL/min/mmHg, respectively) but were unchanged in the non‐loading trial (from 630.7 ± 157.1 to 635.6 ± 195.7 mL/min and from 7.1 ± 1.8 to 7.2 ± 2.9 mL/min/mmHg, respectively). These results show that increasing inspiratory muscle work affects splanchnic blood flow regulation, and we suggest that this might be mediated by the inspiratory muscle‐induced metaboreflex.
Purpose
The aim of the study is to examine the relationships between increments in resting blood flow and isometric maximal voluntary contraction (MVC) force reduction, muscle soreness, and swelling ...after eccentric contractions (ECs).
Methods
Twenty-one young healthy men (age 20.8 ± 1.6 years; height 172.0 ± 5.3 cm; weight 64.9 ± 7.7 kg) were recruited for this study. All participants performed right arm ECs in five sets of 20 repetitions with 3 min of rest between the sets. The dumbbell weight corresponded to 60% MVC force of isometric contraction of elbow flexors with 90° elbow joint angle. Resting forearm blood flow (FBF), the MVC force, the muscle thickness (MT), and muscle soreness of elbow flexors, heart rate (HR), and blood pressure (BP) of brachial artery were measured before, 24 and 48 h after ECs.
Results
Average and peak resting FBF after ECs significantly changed from the average values before ECs (21% and 39% increase, respectively,
P
< 0.01). However, resting HR and BP were not significantly different after ECs. Average increase in resting FBF showed a significant relationship with average isometric MVC force reduction (
r
= − 0.45,
P
< 0.05), peak isometric MVC force reduction (
r
= − 0.48,
P
< 0.05), average muscle soreness (
r
= 0.49,
P
< 0.05), and peak muscle soreness (
r
= 0.49,
P
< 0.05). Moreover, stepwise multiple regression analysis revealed that average increased resting FBF was explained by isometric MVC force reduction and muscle soreness (adjusted
R
2
= 0.33).
Conclusions
These results suggested that increments in resting blood flow reflect muscle damage, and increased resting blood flow may be a result of acute inflammatory response induced by muscle damage.
Acute exercise has been demonstrated to improve cognitive function. In contrast, severe hypoxia can impair cognitive function. Hence, cognitive function during exercise under severe hypoxia may be ...determined by the balance between the beneficial effects of exercise and the detrimental effects of severe hypoxia. However, the physiological factors that determine cognitive function during exercise under hypoxia remain unclear. Here, we examined the combined effects of acute exercise and severe hypoxia on cognitive function and identified physiological factors that determine cognitive function during exercise under severe hypoxia. The participants completed cognitive tasks at rest and during moderate exercise under either normoxic or severe hypoxic conditions. Peripheral oxygen saturation, cerebral oxygenation, and middle cerebral artery velocity were continuously monitored. Cerebral oxygen delivery was calculated as the product of estimated arterial oxygen content and cerebral blood flow. On average, cognitive performance improved during exercise under both normoxia and hypoxia, without sacrificing accuracy. However, under hypoxia, cognitive improvements were attenuated for individuals exhibiting a greater decrease in peripheral oxygen saturation. Cognitive performance was not associated with other physiological parameters. Taken together, the present results suggest that arterial desaturation attenuates cognitive improvements during exercise under hypoxia.
New Findings
What is the central question of this study?
What is the effect of different exercise intensities on sex steroid hormone concentrations in individuals with different degrees of physical ...fitness?
What is the main finding and its importance?
In endurance athletes, serum concentrations of sex steroid hormones increased only with high‐intensity exercise. Moreover, different responses of sex steroid hormone secretions were induced by different exercise intensities in individuals with low and high levels of physical fitness.
Previous studies have shown that acute exercise elevates sex steroid hormone concentrations in rodents and that sprint exercise increases circulating testosterone in healthy young men. However, the effect of different exercise intensities on sex steroid hormone responses at different levels of physical fitness is still unclear. In this study, we compared circulating sex steroid hormone responses at different exercise intensities in athletes and non‐athletes. Eight male endurance athletes and 11 non‐athletes performed two 15 min sessions of submaximal exercise at 40 and 70% peak oxygen uptake (V̇O2 peak ), respectively, and exercised at 90% V̇O2 peak until exhaustion. Venous blood samples were collected during the last minute of each submaximal exercise session and immediately after exhaustion. Acute exercise at 40, 70 and 90% V̇O2 peak induced significant increases in serum dehydroepiandrosterone (DHEA) and free testosterone concentrations in non‐athletes. On the contrary, only 90% V̇O2 peak exercise led to an increase in serum DHEA and free testosterone concentrations in athletes. Serum 5α‐dihydrotestosterone concentrations increased with 90% V̇O2 peak exercise in both athletes and non‐athletes. Additionally, serum estradiol concentrations were significantly increased at moderate and high exercise intensities in both athletes and non‐athletes. These results indicate that in endurance athletes, serum sex steroid hormone concentrations, especially serum DHEA and 5α‐dihydrotestosterone concentrations, increased only with high‐intensity exercise, suggesting that different responses of sex steroid hormone secretion are induced by different exercise intensities in individuals with low and high levels of physical fitness. In athletes, therefore, high‐intensity exercise may be required to increase circulating sex steroid hormone concentrations.
New Findings
What is the central question of this study?
What is the effect of different exercise intensities on sex steroid hormone concentrations in individuals with different degrees of physical fitness?
What is the main finding and its importance?
In endurance athletes, serum concentrations of sex steroid hormones increased only with high‐intensity exercise. Moreover, different responses of sex steroid hormone secretions were induced by different exercise intensities in individuals with low and high levels of physical fitness.
New Findings
What is the central question of this study?
Sympathetic vasomotor outflow is reduced during low‐intensity dynamic leg exercise in younger individuals: does ageing influence the ...sympathoinhibitory effect during low‐intensity leg cycling?
What is the main finding and its importance?
Muscle sympathetic nerve activity during low‐intensity cycling decreased in older males, as seen in young males. It is possible that cardiopulmonary baroreflex‐mediated inhibition of sympathetic vasomotor outflow during dynamic leg exercise is preserved in healthy older males.
Muscle sympathetic nerve activity (MSNA) is reduced during low‐intensity dynamic leg exercise in young males. It is suggested that this inhibition is mediated by loading of the cardiopulmonary baroreceptors. The purpose of this study was to clarify the impact of age on MSNA during dynamic leg exercise. Nine younger males (YM, mean ± SD, 20 ± 1 years) and nine older males (OM, 72 ± 3 years) completed the study. The subjects performed two 4‐min cycling exercises at 10% of their heart rate reserve using a cycle ergometer in a semirecumbent position (MSNA and estimated central venous pressure (eCVP) trials). MSNA was recorded via microneurography of the left radial nerve. The CVP was estimated based on peripheral venous pressure, which was monitored using a cannula in the right large antecubital vein. The magnitude of the increase in mean arterial blood pressure during leg cycling was larger in OM (+9.3 ± 5.5 mmHg) compared with YM (+2.8 ± 4.7 mmHg). MSNA burst frequency was decreased during cycling in both YM (–8.1 ± 3.8 bursts/min) and OM (–10.6 ± 3.3 bursts/min), but no significant difference was found between the two groups. The eCVP increased during exercise in both groups, and there was no difference in the changes in eCVP between YM (+1.1 ± 0.4 mmHg) and OM (+1.2 ± 0.7 mmHg). These data indicate that inhibition of sympathetic vasomotor outflow during low‐intensity cycling appears in OM as seen in YM. It is possible that the muscle pump‐induced loading of the cardiopulmonary baroreflex is preserved during cycling in healthy older males.
Objective
Disuse and/or a non-weight-bearing condition changes muscle composition, with decreased skeletal muscle tissue and increased fat within (intramuscular adipose tissue, IntraMAT) and between ...(intermuscular adipose tissue, InterMAT) given muscles. Excessive adipose tissue contributes to dysfunctional and metabolically impaired muscle. How these adipose tissues change during orthopedic treatment (e.g., cast immobilization, daily use of crutches) is not well documented. This study aimed to quantify changes in IntraMAT, InterMAT, and thigh and calf muscle tissue during orthopedic treatment.
Materials and methods
We studied 8 patients with fifth metatarsal bone or fibular fractures. The ankle joint involved underwent plaster casting for approximately 4 weeks, with crutches used during that time. Axial T1-weighted MRI at the mid-thigh and a 30% proximal site at the calf were obtained to measure IntraMAT and InterMAT cross-sectional areas (CSAs) and skeletal muscle tissue CSA before treatment and 4 weeks afterward.
Results
Thigh and calf muscle tissue CSAs were significantly decreased from before to after treatment: thigh, 85.8 ± 7.6 to 77.1 ± 7.3 cm
2
; calf, 53.3 ± 5.5 to 48.9 ± 5.0 cm
2
(
p
< 0.05). None of the IntraMAT or InterMAT changes was statistically significant. There was a relation between the percentage change of thigh IntraMAT CSA and muscle tissue CSA (r
s
= −0.86,
p
< 0.01).
Conclusions
The 4 weeks of treatment primarily induced skeletal muscle atrophy with less of an effect on IntraMAT or InterMAT. There is a risk of increasing IntraMAT relatively by decreasing skeletal muscle tissue size during orthopedic treatment.
The purpose of this study was to elucidate the effects of hypoxia on deoxygenation and neuromuscular activation in synergistic quadriceps femoris (QF) muscles (i.e., the rectus femoris, vastus ...medialis, vastus intermedius, and vastus lateralis) during submaximal intermittent knee extension. Ten healthy men performed isometric intermittent knee extension exercises with the right leg at 50% of maximal voluntary contraction for 3 min while inhaling a normoxic inspired oxygen (O
) fraction = 0.21 or hypoxic (inspired O
fraction = 0.10-0.12) gas mixture. Muscle deoxygenation was measured by tissue O
saturation (StO
), and neuromuscular activation by root mean square (RMS) of the surface electromyographic signals, from individual muscles of the QF using near-infrared spectroscopy and surface electromyography. StO
was decreased more in hypoxia than normoxia during the exercises, and there was a greater increase in RMS during intermittent knee extension in hypoxia than normoxia in individual muscles of the QF. There were no differences in the ratios of StO
and RMS in hypoxia compared with normoxia between individual muscles of the QF. These findings suggest that submaximal, isometric, and intermittent exercises in hypoxic conditions enhanced muscle oxygen consumption and muscle activity similarly for synergistic muscles.
Abstract It is unclear whether blood flow restriction (BFR) accelerates the adaptation of the time constant (τ) of phase II oxygen uptake ( $$ {\dot{\text{V}}}{\text{O}}_{2} $$ V ˙ O 2 ) kinetics in ...the moderate-intensity exercise domain via moderate-intensity aerobic training. Therefore, healthy participants underwent moderate-intensity 45–60% $$ {\dot{\text{V}}}{\text{O}}_{2} $$ V ˙ O 2 Reserve aerobic cycle training with or without BFR (BFR group, n = 9; CON group, n = 9) for 8 weeks to evaluate $$ {\dot{\text{V}}}{\text{O}}_{2} $$ V ˙ O 2 kinetics during moderate-intensity cycle exercise before (Pre) and after 4 (Mid) and 8 (Post) weeks of training. Both groups trained for 30 min, 3 days weekly. BFR was performed for 5 min every 10 min by applying cuffs to the upper thighs. The τ significantly decreased by Mid in the BFR group (23.7 ± 2.9 s Pre, 15.3 ± 1.8 s Mid, 15.5 ± 1.4 s Post, P < 0.01) and by Post in the CON group (27.5 ± 2.0 s Pre, 22.1 ± 0.7 s Mid, 18.5 ± 1.9 s Post, P < 0.01). Notably, the BFR group’s τ was significantly lower than that of the CON group at Mid (P < 0.01) but not at Post. In conclusion, BFR accelerates the adaptation of the $$ {\dot{\text{V}}}{\text{O}}_{2} $$ V ˙ O 2 kinetics of phase II by moderate-intensity aerobic training.
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