Relationship Between Muscle Deoxygenation and Cardiac Output in Subjects Without Attenuation of Deoxygenation Hemoglobin Concentration Near the End of Ramp Cycling Exercise: A Longitudinal Study.

The aim of this study was to investigate the longitudinal relationship between the slopes of systemic and quadriceps muscle O2 dynamics in subjects without attenuation point in deoxygenated hemoglobin concentration at vastus lateralis (APdeoxy-Hb@VL) during high-intensity cycling. Seven young men without APdeoxy-Hb@VL performed ramp cycling exercise until exhaustion before and after 8 weeks, while continuing recreational physical activities throughout that period. Muscle O2 saturation (SmO2) and deoxy-Hb were monitored at the vastus lateralis (VL) and rectus femoris (RF) by near infrared spectroscopy oximetry during exercise. Cardiac output (CO) was also continuously assessed. During high-intensity exercise, at VL, a significantly steeper slope of deoxy-Hb was found after 8 weeks compared with before, while the slopes of deoxy-Hb at RF were not significantly changed. Though a decrease in the slope of CO after 8 weeks did not reach significance (p = 0.12), the change in the slope of CO was significantly related to the change in the slopes of deoxy-Hb at VL (rs = -0.89, p < 0.01) and RF (rs = -0.86, p < 0.05). Our data reinforces the idea that, in subjects without APdeoxy-Hb@VL, the slope of muscle deoxygenation at VL during high-intensity cycling exercise may partly be explained by systemic O2 supply, rather than O2 balance in other thigh muscles.

Systemic and Quadriceps Muscle O2 Dynamics in Subjects Without Attenuation Point of Deoxygenated Haemoglobin Concentration During Ramp Cycling Exercise.

The aim of this study was to compare systemic and quadriceps muscle O2 dynamics between aerobic capacity-matched subjects without (NAP; n = 5) and with (CON; n = 13) attenuation point in deoxygenated haemoglobin concentration (deoxy-Hb) at vastus lateralis (APdeoxy-Hb@VL) during ramp cycling exercise. Muscle O2 saturation (SmO2) and deoxy-Hb were monitored at the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) by spatial resolved near infrared spectroscopy during exercise. Cardiac output (CO) and pulmonary O2 uptake (VO2) were also continuously measured. During high-intensity exercise, in NAP, steeper slopes of both deoxy-Hb and SmO2 were found at VM, similar to VL muscle. Additionally, at RF, the slope of deoxy-Hb was steeper in NAP than CON. While the slope of pulmonary VO2 was similar between groups, the slope of CO was shallower in NAP than CON. During moderate intensity exercise, the slopes of all variables were similar between groups. These results suggest that the slope of muscle deoxygenation was enhanced not only in VL but also other thigh muscles in NAP, compared to CON. Because the slope of CO was associated with the slope of SmO2 and deoxy-Hb at VL during high-intensity exercise, the differences in subjects with and without APdeoxy-Hb@VL may be partly explained by systemic O2 supply, rather than O2 balance in the other quadriceps muscles.

Skeletal Muscle Deoxygenation and Its Relationship to Aerobic Capacity During Early and Late Stages of Aging.

The aim of this study was to compare muscle O2 dynamics during exercise among elderly (n = 10, age: 73 ± 3 years), middle-aged (n = 9, age: 50 ± 6 years), and young (n = 10, age: 25 ± 3 years) adults. The subjects performed ramp bicycle exercise until exhaustion. Muscle O2 saturation (SmO2) and relative changes from rest in oxygenated hemoglobin/myoglobin (∆oxy-Hb/Mb), deoxygenated hemoglobin/myoglobin (∆deoxy-Hb/Mb), and total hemoglobin concentration (∆total-Hb) were monitored continuously at the vastus lateralis muscle by near-infrared spatial resolved spectroscopy. At given absolute workloads, SmO2 and ∆oxy-Hb/Mb were significantly lower in elderly than the other groups, while ∆deoxy-Hb/Mb, ∆total-Hb, and pulmonary O2 uptake (VO2) were similar among the three groups. In contrast, there were no significant differences in muscle O2 dynamics during submaximal exercise between middle-aged and young subjects. Muscle O2 dynamics may be relatively preserved in early stages of aging, although muscle deoxygenation is enhanced in late stages of aging, probably due to reduced convective O2 supply. Moreover, change in SmO2 was significantly positively correlated with peak VO2 in the elderly, while a significant negative relationship was observed in middle-aged and young subjects. In late stages of aging, diminished peak VO2 may be caused by attenuated convective O2 transport, while reduced peak VO2 can be explained by lowered muscle O2 extraction in early stages of aging.

Differences in Muscle O2 Dynamics During Treadmill Exercise Between Aerobic Capacity-Matched Overweight and Normal-Weight Adults.

The aim of this study was to compare muscle O2 dynamics during exercise between aerobic capacity-matched overweight and normal-weight adults. Overweight women (OW, n = 9) and normal-weight women (NW, n = 14) performed graded treadmill exercise until exhaustion. Muscle O2 saturation (SmO2) and relative changes from rest in deoxygenated hemoglobin concentration (∆deoxy-Hb) and total hemoglobin concentration (∆total-Hb) were monitored continuously at gastrocnemius medialis muscle by near infrared spatial resolved spectroscopy. Significantly higher SmO2 and lower ∆deoxy-Hb and ∆total-Hb were observed in OW compared with NW. Pulmonary O2 uptake (VO2) normalized by fat-free mass was matched between groups. In both groups, peak VO2 was significantly correlated with change in SmO2 and ∆deoxy-Hb. Our findings suggest that both muscle blood volume and deoxygenation were lower in overweight adults, compared to aerobic capacity-matched normal-weight adults. Moreover, lowered muscle O2 extraction was related to peak VO2 in overweight adults, as well as in normal-weight adults.

Effects of Aerobic Cycling Training on O2 Dynamics in Several Leg Muscles in Early Post-myocardial Infarction.

The aim of this study was to test the effects of aerobic cycling training on O2 dynamics in several leg muscles in early post-myocardial infarction (post-MI). Fifteen post-MI patients were divided into a 12-week training group (TR, n = 9) or a control/non-training group (CON, n = 6). All participants performed ramp bicycle exercise until exhaustion at two times: within 12-35 days of their MI and then again 12 weeks later. Muscle O2 saturation (SmO2) and total hemoglobin concentration (∆total-Hb) were monitored continuously at thigh and lower leg muscles by near infrared spectroscopy. In CON, there were no significant alterations in muscle O2 dynamics between before and after 12 weeks at any measurement sites. In TR, after 12 weeks, lower SmO2 was observed at all measurement sites. In total-Hb, no significant changes were found after training at any measurement sites in TR. Moreover, the muscle deoxygenation after 12 weeks was related to an improvement of peak O2 uptake in all muscles. Our findings suggest that aerobic cycling training may be useful for early post-MI patients to improve peak aerobic capacity via enhancement of muscle deoxygenation and O2 extraction at several leg muscles.

Changes in the Width of the Tibiofibular Syndesmosis Related to Lower Extremity Joint Dynamics and Neuromuscular Coordination on Drop Landing During the Menstrual Cycle.

BACKGROUND: Many injuries of the lower extremities, especially the knee and ankle, occur during sports activity, and the incidence rate is higher in women than in men. HYPOTHESIS: The hypothesis was that phases of the menstrual cycle affect the width of the tibiofibular syndesmosis during drop landing in healthy young women and that such changes at the tibiofibular joint also affect the dynamics and neuromuscular coordination of the lower extremities. STUDY DESIGN: Descriptive laboratory study. METHODS: Participants included 28 healthy young women (mean age, 21.0 ± 0.8 years). Blood samples were collected to determine plasma levels of estradiol and progesterone immediately before the performance of the task: drop landing on a single leg from a 30-cm platform. Using ultrasonography, the distance between the tibia and the distal end of the fibula, regarded as the width of the tibiofibular syndesmosis, was measured in an upright position without flexion of the ankle. The peak ground-reaction force (GRF) on landing was measured using a force platform. The time to peak GRF (Tp-GRF) was measured as the time from initial ground contact to the peak GRF. Hip, knee, and ankle joint angles during the single-leg landing were calculated using a 3-dimensional motion analysis system. Muscle activities of the lower extremities were measured using surface electromyography. RESULTS: The width of the tibiofibular syndesmosis was significantly greater in the luteal phase when compared with the menstrual, follicular, and ovulation phases (by 5%-8% of control). Also, during the luteal phase, the Tp-GRF was significantly shorter than in the follicular phase (by 6%); hip internal rotation and knee valgus were significantly greater than in the menstrual phase (by 43% and 34%, respectively); knee flexion was significantly less than in the menstrual and follicular phases (by 7%-9%); ankle dorsiflection was significantly less than in the follicular phase (by 11%); ankle adduction and eversion were significantly greater than in the menstrual and follicular phases (by 26%-46%, and 27%-33%, respectively); and activation of the gluteus maximus before landing was significantly lower than in the menstrual and follicular phases (by 20%-22%). CONCLUSION: The luteal phase appears to be associated with decreased strength and laxity of the ankle as well as lower extremity muscle activity in women. The changes presumably represent a greater risk for sports injuries. CLINICAL RELEVANCE: The results of this study suggest that the luteal phase may be related to the greater incidence of lower extremity injuries in women.

Multi-site Measurements of Muscle O2 Dynamics During Cycling Exercise in Early Post-myocardial Infarction.

The aim of this study was to compare the muscle oxygen dynamics between early post-myocardial infarction (n = 12; MI) and age-matched elderly subjects without MI (n = 12; CON) in several leg muscles during ramp cycling exercise. Muscle oxygen saturation (SmO2), deoxygenated-hemoglobin concentration (∆deoxy-Hb), and total-hemoglobin concentration (∆total-Hb) were monitored continuously at the distal site of vastus lateralis (VLd), proximal site of the vastus lateralis (VLp), rectus femoris (RF), vastus medialis (VM), gastrocnemius medialis (GM), and tibialis anterior (TA) muscles by near infrared spatial resolved spectroscopy. At given absolute workloads, higher SmO2 was observed at VLd, VLp, RF, and VM in MI, compared to CON. Simultaneously, in MI, deoxy-Hb was lower at VLd, VLp, and VM than CON. In contrast to the thigh muscles, muscle oxygen dynamics were similar between groups in GM and TA. In total-Hb, no significant differences were found at any measurement sites. These results demonstrated that the absence of muscle deoxygenation was observed in MI muscles, especially in the thigh muscles, but not in the lower leg muscles.

The Effects of Passive Cycling Exercise for 20 min on Cardiorespiratory Dynamics in Healthy Men [corrected].

An increase in the incidence rate of cardiovascular disease is attributed to high daily sitting time, while a drop in risk of cardiovascular disease comes from a decrease in daily sitting time, rather than an increase in physical activity levels. Although short-duration passive exercise increases energy expenditure and blood flow, few studies have reported on the responses of cardiorespiratory dynamics to long-duration passive exercise. The purpose of this study was to consider the effect of long-duration passive exercise for 20 min on cardiorespiratory and muscle oxygen dynamics. Eight healthy men continuously performed passive exercise using a cycle ergometer for 20 min at 50 rpm. Changes in oxygen uptake, cardiac output and muscle oxygenation were measured during passive cycling exercise. The oxygen uptake at 1 min after the start of passive exercise was significantly increased, compared to resting level, but subsequently returned to the same as resting level. Cardiac output showed no change during passive cycling exercise. Tissue oxygen saturation increased after the start of passive exercise and subsequently maintained steady state. These results suggest that the effect of increases in energy expenditure was not maintained by passive exercise for 20 min. In addition, it is likely that passive cycling exercise for 20 min has an effect on peripheral circulation, although the exercise seems to have no effect on central circulation.

Low Volume Aerobic Training Heightens Muscle Deoxygenation in Early Post-Angina Pectoris Patients.

The aim of this study was to investigate the effect of low volume aerobic exercise training on muscle O2 dynamics during exercise in early post-angina pectoris (AP) patients, as a pilot study. Seven AP patients (age: 72 ± 6 years) participated in aerobic exercise training for 12 weeks. Training consisted of continuous cycling exercise for 30 min at the individual's estimated lactate threshold, and the subjects trained for 15 ± 5 exercise sessions over 12 weeks. Before and after training, the subjects performed ramp cycling exercise until exhaustion. Muscle O2 saturation (SmO2) and relative changes from rest in deoxygenated hemoglobin concentration (∆Deoxy-Hb) and total hemoglobin concentration (∆Total-Hb) were monitored at the vastus lateralis by near infrared spatial resolved spectroscopy during exercise. The SmO2 was significantly lower and ∆Deoxy-Hb was significantly higher after training than before training, while there were no significant changes in ∆Total-Hb. These results indicated that muscle deoxygenation and muscle O2 extraction were potentially heightened by aerobic exercise training in AP patients, even though the exercise training volume was low.

Muscle Deoxygenation and Its Heterogeneity Changes After Endurance Training.

The purpose of this study was to elucidate the time course of muscle deoxygenation and its heterogeneity changes through endurance training. Nine healthy untrained male participated in this study. The subjects performed a ramp incremental cycle exercise protocol to estimate VO2peak and muscle tissue oxygen saturation (SmO2) distribution in the VL muscle before and after 3 (3 wk-T) and 6 weeks of endurance training (6 wk-T). The probe of multi-channel near infrared spatially resolved spectroscopy was attached to the left vastus lateralis muscle along the direction of the long axis. The subjects performed cycle exercise at 60 % of VO2peak for 30 min/day, 3 days/week as the endurance training. After the training, VO2peak at 3 wk-T and 6 wk-T were significantly increased compared to pre-training (Pre-T) and VO2peak at 6 wk-T was significantly increased compared to 3 wk-T. Mean SmO2 within measurement sites at VO2peak was significantly decreased after 3 wk-T and 6 wk-T compared to Pre-T, but mean SmO2 was not significantly different between 3 wk-T and 6 wk-T. Conversely, the heterogeneity of the SmO2 during exercise was not significantly changed through endurance training. A significantly negative correlation was found between ΔVO2 and ΔSmO2 after the first 3 weeks of endurance training. In contrast, no correlation was found betweenΔVO2 and ΔSmO2 after the last 3 weeks of endurance training. These results suggest that the enhanced muscle O2 availability may be one of the primary factors in increasing VO2peak after the first 3 weeks of endurance training.

Muscle Oxygen Dynamics During Cycling Exercise in Angina Pectoris Patients.

Muscle O2 dynamics during ramp cycling exercise were compared between angina pectoris patients (AP; n = 7, age: 73 ± 6 years) after coronary artery bypass grafting and age-, height-, and body weight-matched elderly control subjects (CON; n = 7, age: 74 ± 8 years). Muscle O2 saturation (SmO2) and relative change in deoxygenated (∆deoxy-Hb) and total hemoglobin concentration (∆total-Hb) were measured continuously during exercise in the vastus lateralis (VL) by near infrared spatial resolved spectroscopy. Pulmonary O2 uptake (VO2) was also monitored throughout exercise to determine peak VO2. In AP, SmO2 was significantly higher, and ∆deoxy-Hb was significantly lower during exercise, compared to CON. In all subjects, ∆SmO2 (values at peak exercise minus values at resting) was negatively correlated to peak VO2 (r = -0.52, p < 0.05), and ∆deoxy-Hb at peak exercise tended to be negatively associated with peak VO2 (r = 0.48, p = 0.07). Blunted skeletal muscle deoxygenation response was observed in AP patients, which may be related to lower aerobic capacity in AP patients.

Regional Differences of Metabolic Response During Dynamic Incremental Exercise by (31)P-CSI.

The aim of this study was to detect the differences in muscle metabolic response of the quadriceps during incremental dynamic knee exercise using regional (31)Phosphorus Chemical Shift Imaging ((31)P-CSI). Sixteen healthy men participated in this study (age 28 ± 5 years, height 171.4 ± 3.9 cm, weight 67.1 ± 9.8 kg). The experiments were carried out with a 1.5-T superconducting magnet with a 5-in. diameter circular surface coil. The subjects performed isometric unilateral knee extension exercise to detect their maximum voluntary contraction (MVC) in prone position. Then they performed dynamic unilateral knee extension exercise in the magnet at 10, 20, 30 and 40 % of their MVC with the transmit-receive coil placed under the right quadriceps. The subjects pulled down a rope with the adjusted weight attached to the ankle at a frequency of 0.5 Hz for 380 s. Intracellular pH (pHi) was calculated from the median chemical shift of the inorganic phosphate (Pi) peak relative to phosphocreatine (PCr). The quadriceps were divided into three regions, (1) medial, (2) anterior, (3) lateral, and in comparison, there was no significant difference in Pi/PCr nor in pHi between regions, except Pi/PCr of the medial region was significantly higher than the anterior region at maximum intensity (p < 0.05). These results suggest that regional muscle metabolic response is similar in the quadriceps except at maximum intensity.

Effects of Acupuncture Stimulation on Muscle Tissue Oxygenation at Different Points.

Muscle tissue oxygenation is a critical issue in muscle complications such as pain, exhaustion, stiffness, or fatigue during and after exercise. The aim of this study was to investigate whether the changes of muscle tissue oxygenation could be observed at both erector spinae muscle at S1 level and gastrocnemius during and after acupuncture stimulation to ipsilateral erector spinae at S1 level. The subjects were ten healthy males. Muscle oxygenation was monitored by near infrared spectroscopy (NIRS), and the probes were placed on the right side of the erector spinae muscle at S1 level (Guanyuanshu, BL26) and the belly of the gastrocnemius on the right (Chengjin, BL56). The subjects lay on the bed in prone position for 10 min, followed by acupuncture insertion into the right side of BL26. The needle was left for 10 min and subjects were kept still for 10 min after removal. At BL26, oxygenated-hemoglobin (oxy-Hb) was significantly increased compared to the baseline at 10 min after insertion (p < 0.05), then continued increasing. Total hemoglobin (t-Hb) was increased at 2 min after removal (p < 0.05). Tissue-oxygen saturation (StO2) was increased at 7 min after insertion (p < 0.05). At BL56, oxy-Hb and t-Hb were increased at 6 and 2 min after removal, respectively (p < 0.05). StO2 showed no significant change. The acupuncture stimulation affected muscle tissue oxygenation differently at both stimulated and non-stimulated points in the same innervation.

Regional Differences in Muscle Energy Metabolism in Human Muscle by 31P-Chemical Shift Imaging.

Previous studies have reported significant region-dependent differences in the fiber-type composition of human skeletal muscle. It is therefore hypothesized that there is a difference between the deep and superficial parts of muscle energy metabolism during exercise. We hypothesized that the inorganic phosphate (Pi)/phosphocreatine (PCr) ratio of the superficial parts would be higher, compared with the deep parts, as the work rate increases, because the muscle fiber-type composition of the fast-type may be greater in the superficial parts compared with the deep parts. This study used two-dimensional 31Phosphorus Chemical Shift Imaging (31P-CSI) to detect differences between the deep and superficial parts of the human leg muscles during dynamic knee extension exercise. Six healthy men participated in this study (age 27±1 year, height 169.4±4.1 cm, weight 65.9±8.4 kg). The experiments were carried out with a 1.5-T superconducting magnet with a 5-in. diameter circular surface coil. The subjects performed dynamic one-legged knee extension exercise in the prone position, with the transmit-receive coil placed under the right quadriceps muscles in the magnet. The subjects pulled down an elastic rubber band attached to the ankle at a frequency of 0.25, 0.5 and 1 Hz for 320 s each. The intracellular pH (pHi) was calculated from the median chemical shift of the Pi peak relative to PCr. No significant difference in Pi/PCr was observed between the deep and the superficial parts of the quadriceps muscles at rest. The Pi/PCr of the superficial parts was not significantly increased with increasing work rate. Compared with the superficial areas, the Pi/PCr of the deep parts was significantly higher (p<0.05) at 1 Hz. The pHi showed no significant difference between the two parts. These results suggest that muscle oxidative metabolism is different between deep and superficial parts of quadriceps muscles during dynamic exercise.

Sex-Related Difference in Muscle Deoxygenation Responses Between Aerobic Capacity-Matched Elderly Men and Women.

Muscle O2 dynamics during ramp cycling exercise were compared between aerobic capacity-matched elderly men (n=8, age 65±2 years) and women (n=8, age 66±3 years). Muscle O2 saturation (SmO2) and relative change in deoxygenated (Δdeoxy-Hb) and total hemoglobin concentration (Δtotal-Hb) were monitored continuously during exercise in the vastus lateralis (VL) and gastrocnemius medialis (GM) by near infrared spatial resolved spectroscopy. SmO2 was significantly higher during exercise in women than in men in VL, but not in GM. In VL, Δdeoxy-Hb and Δtotal-Hb were significantly higher in men than in women, especially during high intensity exercise. However, no significant difference was observed in Δdeoxy-Hb or Δtotal-Hb in GM. Sex-related differences in muscle deoxygenation response may be heterogeneous among leg muscles in elderly subjects.

Effects of Low Volume Aerobic Training on Muscle Desaturation During Exercise in Elderly Subjects.

Aging enhances muscle desaturation responses due to reduced O2 supply. Even though aerobic training enhances muscle desaturation responses in young subjects, it is unclear whether the same is true in elderly subjects. Ten elderly women (age: 62±4 years) participated in 12-weeks of cycling exercise training. Training consisted of 30 min cycling exercise at the lactate threshold. The subjects exercised 15±6 sessions during training. Before and after endurance training, the subjects performed ramp cycling exercise. Muscle O2 saturation (SmO2) was measured at the vastus lateralis by near infrared spectroscopy during the exercise. There were no significant differences in SmO2 between before and after training. Nevertheless, changes in peak pulmonary O2 uptake were significantly negatively related to changes in SmO2 (r=-0.67, p<0.05) after training. Muscle desaturation was not enhanced by low volume aerobic training in this study, possibly because the training volume was too low. However, our findings suggest that aerobic training may potentially enhance muscle desaturation at peak exercise in elderly subjects.

Aerobic training enhances muscle deoxygenation in early post-myocardial infarction.

PURPOSE: Exercise-induced skeletal muscle deoxygenation is startling by its absence in early post-myocardial infarction (MI) patients. Exercise training early post-MI is associated with reduced cardiovascular risk and increased aerobic capacity. We therefore investigated whether aerobic training could enhance the muscle deoxygenation in early post-MI patients. METHODS: 21 ± 8 days after the first MI patients (n = 16) were divided into 12-week aerobic training (TR, n = 10) or non-training (CON, n = 6) groups. Before and after intervention, patients performed ramp bicycle exercise until exhaustion. Muscle deoxygenation was measured at vastus lateralis by near-infrared spectroscopy during exercise. RESULTS: Aerobic training significantly increased peak oxygen uptake (VO2) (18.1 ± 3.0 vs. 22.9 ± 2.8 mL/kg/min), decreased the change in muscle oxygen saturation from rest to submaximal and peak exercise (∆SmO2; 2.4 ± 5.7 vs. -7.0 ± 3.4 %), and increased the relative change in deoxygenated hemoglobin/myoglobin concentration from rest to submaximal (-1.5 ± 2.3 vs. 3.0 ± 3.6 µmol/L) and peak exercise (1.1 ± 4.5 vs. 8.2 ± 3.5 µmol/L). Change in total hemoglobin/myoglobin concentration in muscle was not significantly affected by training. In CON, no significant alterations were found after 12 weeks in either muscle deoxygenation or peak VO2 (18.6 ± 3.8 vs. 18.9 ± 4.6 mL/kg/min). An increase in peak VO2 was significantly negatively correlated with change in ∆SmO2 (r = -0.65) and positively associated with change in ∆deoxy-Hb/Mb at peak exercise (r = 0.64) in TR. CONCLUSIONS: In early post-MI patients, aerobic training enhanced skeletal muscle deoxygenation, and the enhancement was related to increased aerobic capacity.

Gender difference in distance of tibiofibular syndesmosis to joint dynamics of lower extremities during squat.

The incidence of lower extremity injury is greater in women than men, indicating gender difference in lower extremity function. Here we investigate the role of the ankle during squatting in young men and women by measuring the tibiofibular syndesmosis (TFS) distance and the angles of hip, ankle and knee joints. TFS distance was positively correlated to body mass in men, but not in women, suggesting some factor(s) affecting TSF distance in women. When divided into two groups with wide and narrow TFS distances, men apparently used ankle and hip joints evenly during squatting, but women, specifically those with a narrow TFS distance, used the hip joint more effectively than ankle. Estimated knee moment was positively correlated to TFS distance in women, but not in men. These results suggest that the women possessing a wider TFS distance use ankle function rather than hip junction when performing lower-extremity exercises (i.e. squatting), presumably accounting for the higher incidence of ankle injury in women during such activities.

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.