Glucose loading for heart failure protects the myocardium and improves physical function.

[Purpose] The purpose of this study was to investigate the effects of glucose intake on physical function in a heart failure rat model. [Materials and Methods] Five-week-old male Wistar rats were used for this study. Monocrotalin (40 mg/kg) was administered intraperitoneally to rats to induce heart failure. The rats were divided into two groups, control and MCT; the MCT group was further classified according to glucose concentration (0%, 10%, and 50%). [Results] Glucose intake during heart failure prevented the loss of body weight, skeletal muscle, and fat mass. Myocardial metabolism in heart failure was enhanced by hypoxia, which in turn, enhanced the glycolytic system. [Conclusion] Glucose loading suppressed cardiac hypertrophy and improved physical function in the heart failure rat model.

Preoperative Factors Affecting Patient-reported Outcome Measures for Total Knee Arthroplasty.

Objectives: The aim of this study was to investigate the preoperative factors affecting health-related quality of life (HRQOL) at 3 and 12 months after total knee arthroplasty (TKA). Methods: In total, 156 patients who underwent unilateral TKA for knee osteoarthritis were included in the study. The Knee Injury and Osteoarthritis Outcome Score (KOOS) was used as a measure of HRQOL before surgery and 3 and 12 months post-TKA. The Modified Gait Efficacy Scale (mGES) score, tibiofemoral angle, rest pain, walking pain, knee joint range of motion, knee joint extensor strength, and walking speed were recorded preoperatively. Pearson's correlation coefficient and the correlation ratio were used to calculate the correlation between KOOS and preoperative factors at 3 and 12 months post-TKA. Multiple regression analysis was performed using the stepwise method with the five postoperative KOOS subscales as dependent variables and the other preoperative factors as independent variables. Results: Preoperative mGES scores were significantly correlated with KOOS Activities of Daily Living, Sport/Rec, and QOL subscores at 3 months post-TKA and with all five KOOS subscales at 12 months post-TKA. Multiple regression analysis identified mGES as an influencing factor for all KOOS subscales except Pain at 3 months post-TKA and all KOOS subscales except Symptoms at 12 months post-TKA. Conclusions: Preoperative walking self-efficacy influenced HRQOL at 3 and 12 months post-TKA. Psychological factors such as self-efficacy should be considered when predicting postoperative outcomes.

Association between foot posture and tibiofemoral contact forces during barefoot walking in patients with knee osteoarthritis.

BACKGROUND: Accumulating evidence indicates that abnormal foot posture are risk factors for knee osteoarthritis (OA). However, the relationship between foot posture and tibiofemoral contact force (CF) during habitual weight-bearing activities remains unclear. This study aimed to determine the association between tibiofemoral CF and foot posture while walking. METHODS: In total, 18 patients with knee OA and 18 healthy individuals participated in this cross-sectional study. Foot parameters were evaluated by Foot Posture Index (FPI), Staheli Arch Index (SAI), hallux valgus angle, calcaneus inverted angle relative to the floor as a static rearfoot posture, navicular height, and toe grip strength. In addition, all participants underwent kinetic and kinematic measurements during a self-selected speed gait. The measurement device used was the three-dimensional motion analysis system with a sampling rate of 120 Hz. The musculoskeletal model, which has 92 Hill-type muscle-tendon units with 23 degrees of freedom, was used to calculate tibiofemoral CF. Partial correlations was used to investigate the association between foot parameters and total, medial, and lateral tibiofemoral CF of the first and second peaks while controlling for gait speed. RESULTS: A significant negative correlation was observed between Walking SAI and first peak medial tibiofemoral CF in control participants (r = -0.505, p = 0.039). SAI was also significantly positively correlated with first peak medial tibiofemoral CF in patients with knee OA (r = 0.482, p = 0.042). CONCLUSIONS: Our findings revealed a correlation between the medial first peak tibiofemoral CF and the SAI. This study indicates that people with knee OA and flatfoot have excessive first medial tibiofemoral CF during walking.

The Effects of Branched-Chain Amino Acids on the Akt/mTOR Pathway and Nebulin Protein in Joint Fixation-Induced Muscle Atrophy.

It is well known that branched-chain amino acids (BCAAs) promote protein synthesis in skeletal muscle and can cause muscle hypertrophy. However, it has also been reported that they may inhibit muscle atrophy induced by load-bearing and age-related changes. In this study, we investigated the effects of BCAA intake during joint fixation on the levels of protein kinase B (Akt), mammalian target of rapamycin (mTOR), and nebulin in a rat model of joint fixation. Akt and mTOR are signal factors of protein synthesis, whereas nebulin is a structural protein in the muscle. The effects of BCAAs on muscle atrophy were also investigated. The phosphorylation rate of mTOR was higher than that of Akt and increased with BCAA intake in the rat hind limb muscles (soleus) when the ankle joint was fixed. The relative level of nebulin and the phosphorylation rate of Neural Wiskott-Aldrich syndrome protein (N-WASP) also increased as a result of BCAA intake during fixation. This is important because nebulin and N-WASP are involved in the formation of the structure of sarcomere thin filaments. Furthermore, when the cross-sectional areas (CSAs) of different types of muscle fibers were measured during histological evaluation of muscle atrophy, it was found that the inhibitory effect of BCAA on muscle atrophy was higher in Type 1 fibers. Additionally, a positive correlation was found between nebulin level and the CSAs of the muscle fibers. It was found that there is a close relationship between the content of structural proteins and muscle atrophy.

Long-term wheel-running prevents reduction of grip strength in type 2 diabetic rats.

Diabetic skeletal muscles show reduced contractile force and increased fatigability. Hands are a target for several diabetes-induced complications. Therefore, reduced handgrip strength often occurs as a consequence of diabetes. The aim of this study was to examine whether long-term exercise can prevent reduction of grip strength in type 2 diabetes mellitus (T2DM) model OLETF rats, and to explore the mechanisms underlying diabetes-induced grip strength reduction. Ten 5-week-old OLETF rats were used as experimental animals, and five non-diabetic LETO rats as controls of OLETF rats. Half OLETF rats performed daily voluntary wheel-running for 17 months (OLETF + EXE), and the rest of OLETF and LETO rats were sedentary. Grip strength was higher in OLETF + EXE and LETO groups than in OLETF group. OLETF group with hyperglycemia showed an increase in HbA1c, serum TNF-α, and muscle SERCA activity, but a decrease in circulating insulin. Each fiber area, total fiber area, and % total fiber area in type IIb fibers of extensor digitorum longus muscles were larger in OLETF + EXE and LETO groups than in OLETF group. There was a positive correlation between grip strength and the above three parameters concerning type IIb fiber area. Therefore, type IIb fiber atrophy may be the major direct cause of grip strength reduction in OLETF group, although there seems multiple etiological mechanisms. Long-term wheel-running may have blocked the diabetes-induced reduction of grip strength by preventing type IIb fiber atrophy. Regular exercise may be a potent modality for preventing not only the progression of diabetes but muscle dysfunction in T2DM patients.

Physical Fitness Testing and Screening Reveal a Gateway to Identify Locomotive Disorders: Retrospective Study of a Japanese Elementary School Population.

This retrospective epidemiological study investigated the relationship between physical fitness testing and locomotive disorder screening results among elementary school children in Japan. The test and screening results of 1033 children from a single elementary school between 2016 and 2018 were examined. Multiple regression analysis was performed for each gender of children of grades third and fourth to generate receiver-operating characteristic curves. Of the 69 children with parent-identified locomotor problems, 29 (42%) had physical fitness test score of mean ± 2 SD. For the standing long jump test in fourth grade girls, the results differed significantly (P < .001; cut-off, 127 cm) for children whose parents did (n = 7) and did not (n = 84) suspect a possible locomotive disorder. Physical fitness testing in combination with school-based screening for locomotive disorders may be useful for identifying and accurately diagnosing these disorders in children.

Effects of appropriate-intensity treadmill exercise on skeletal muscle and respiratory functions in a rat model of emphysema.

The number of patients with chronic obstructive pulmonary disease (COPD), a typical respiratory disorder, is rapidly increasing globally. The purpose of this study was to determine the effects of appropriate-intensity treadmill exercise on skeletal muscle and respiratory functions in a rat model of emphysema. Twenty-one Wistar rats were randomly divided into three groups: the sham (SH) group, pulmonary emphysema (PE) group, and emphysema + exercise (EX) group. Cigarette smoke solution and lipopolysaccharide were intratracheally administered for 4 weeks in the PE and EX groups. The rats in the EX group were made to run on treadmills in the latter 2 weeks of the experiment. Lung tissue was stained with anti-macrophage antibodies; the specific force (contractile force per unit cross-sectional area) of the diaphragm and hind-limb muscles was measured, and blood was analyzed for serum cytokine levels. Many macrophages were observed in the lung tissue of the PE group. In the EX group, the population of macrophages was smaller, and the specific force of the diaphragm and extensor digitorum longus muscles was higher than in the PE group. Moreover, the degree of inflammation in the pulmonary tissue was reduced in the EX group. These results suggest that adaptive exercise may improve not only respiratory and muscle functions but also inflammation of the pulmonary tissue associated with emphysema.

Possible effects of whole body vibration on bone properties in growing rats.

OBJECTIVES: To examine the effects of whole body vibration (WBV) on bone properties in growing rats, and to explore the optimal conditions for enhancing bone properties. METHODS: Thirty-six 4-week-old male rats were divided into 1 control and 5 experimental groups. Each experimental group underwent WBV at 15, 30, 45, 60, and 90 Hz (0.5 g, 15 min/d, 5 d/wk) for 8 weeks. We measured bone size, muscle weight and bone mechanical strength of the right tibia. Trabecular bone mass and trabecular bone microstructure (TBMS) of the left tibia were analyzed by micro-computed tomography. Serum levels of bone formation/resorption markers were also measured. RESULTS: WBV at 45 Hz and 60 Hz tended to enhance trabecular bone mass and TBMS parameters. However, there was no difference in maximum load of tibias among all groups. Serum levels of bone resorption marker were significantly higher in the 45-Hz WBV group than in the control group. CONCLUSIONS: WBV at 45-60 Hz may offer a potent modality for increasing bone mass during the period of rapid growth. Further studies are needed to explore the optimal WBV conditions for increasing peak bone mass and TBMS parameters. WBV modality may be a potent strategy for primary prevention against osteoporosis.

Association between changes in subcutaneous fat mass and heart failure-induced cachexia: a case report.

[Purpose] We investigated whether an increase or decrease in subcutaneous fat mass secondary to cardiac cachexia can be evaluated using diagnostic ultrasonography in patients with heart failure. [Participant and Methods] We report a case of cardiac cachexia in a patient in whom cachexia was confirmed by weight loss, decreased dietary intake, and biochemical indicators measured by blood tests. We measured the subcutaneous fat mass in the patient's thigh using ultrasonic diagnostic equipment during the cachectic state, as well as 1 and 2 months later. [Results] An increase in weight and ultrasonographically documented femoral subcutaneous fat mass was confirmed by improvement in heart failure-induced cachexia. [Conclusion] Clinically convenient ultrasonic diagnostic equipment is useful to assess subcutaneous fat mass, which serves as an indicator of the degree of cachexia.

Whole body vibration at low-frequency can increase trabecular thickness and width in adult rats.

OBJECTIVE: This study aimed to examine whether WBV becomes a possible modality for the primary prevention of osteoporosis by exploring WBV frequency that has positive effects on bone properties in adult rats. METHODS: Thirty-six 24-week-old rats were divided into one control and 5 experimental groups, which underwent WBV at various frequencies (15, 30, 45, 60 or 90 Hz), with a magnitude of 0.5 g, for 15 min/day, 5 days/week, for 8 weeks. Bone size, muscle weight and bone mechanical strength were measured at the end of experimental period. Bone mass, trabecular bone microarchitecture (TBMA) and cortical bone geometry were analyzed by micro-CT. Circulating bone formation/resorption markers were determined by ELISA. RESULTS: Body weight-corrected soleus weight in all experimental groups and body weight-corrected extensor digitorum longus muscle weight in the 15 and 30 Hz groups were significantly higher than those of the control group, respectively. Femur trabecular thickness and width were significantly higher in the 15 Hz group than in the control group. However, there was no difference in bone mechanical strength or bone formation/resorption markers among all groups. CONCLUSION: These results suggest that WBV at low-frequencies may become a potent modality for the primary prevention of osteoporosis in adults.

Oxygen therapy may worsen the survival rate in rats with monocrotaline-induced pulmonary arterial hypertension.

Although oxygen therapy rapidly improves arterial oxygen saturation in idiopathic pulmonary arterial hypertension, the effects of chronic administration of oxygen are unknown. The purpose of the present study was to investigate the effects of chronic oxygen therapy on the histological changes and survival rate in rats with idiopathic pulmonary arterial hypertension. Idiopathic pulmonary arterial hypertension was induced by monocrotaline injection. The rats were then randomly assigned to receive or not receive oxygen therapy (O2 group and non-O2 group, respectively). The rats in the O2 group were exposed to a high (90%) oxygen environment from day 17 following injection of monocrotaline, when hypoxemia was first observed. The pulmonary arteriole walls were significantly thicker in monocrotaline-injected rats than in saline-injected rats as vehicle on day 19 and were significantly thicker in the rats that received oxygen therapy than in the rats that did not. Right ventricular inflammations were significantly higher in monocrotaline-injected rats than in saline-injected rats on day 19 and were significantly higher in the rats that received oxygen therapy than in the rats that did not. By day 20 after injection of monocrotaline, the survival rate was significantly lower in the rats that received oxygen therapy than in those that did not. Superoxide dismutase activity in the lungs was higher in monocrotaline-injected rats than in saline-injected rats on day 19 after monocrotaline injection and was also higher in the saline-injected rats that received oxygen therapy than in the saline-injected rats that did not. No interaction was detected between monocrotaline injection and oxygen therapy. These results suggest that chronic oxygen therapy worsens the histological changes and survival rate in idiopathic pulmonary arterial hypertension. The fact that degradation of the histological changes and survival rate was accompanied by increase in superoxide dismutase activity suggests that antioxidant capacity may contribute to the degradation.

Long-Term Intake of Green Tea Extract Causes Mal-Conformation of Trabecular Bone Microarchitecture in Growing Rats.

The purpose of this study was to examine the effects of green tea extract (GTE) intake on bone structural and physiological properties, such as bone mass, trabecular bone microarchitecture, cortical bone geometry, and bone mechanical strength, in growing rats. Four-week-old male Wistar rats were divided into the following four groups: standard diet feeding for 85 days (S-CON) or 170 days (L-CON), and GTE diet feeding for 85 days (S-GTE) or 170 days (L-GTE). At the end of the experiment, in addition to measurement of circulating bone formation/resorption markers, bone mass, trabecular bone microarchitecture, and cortical bone geometry were analyzed in the left femur, and bone mechanical strength of the right femur was measured. There was no difference in all bone parameters between the S-CON and S-GTE groups. On the other hand, the L-GTE group showed the decrease in some trabecular bone mass/microarchitecture parameters and no change in cortical bone mass/geometry parameters compared with the L-CON group, and consequently the reduction in bone weight corrected by body weight. There was no difference in bone formation/resorption markers and bone mechanical strength between the S-CON and S-GTE groups and also between the L-CON and L-GTE groups. However, serum leptin levels were significantly lower in the L-GTE group than in the L-CON group. Thus, the long-term GTE intake had negative effects on bone, especially trabecular bone loss and microarchitecture mal-conformation, in growing rats.

Relationship Between Muscle Strength Asymmetry and Body Sway in Older Adults.

The purpose of this study was to investigate the relationship between muscle strength asymmetry and body sway while walking. We studied 63 older adult women. Strong side and weak side of knee extension strength, toe grip strength, hand grip strength, and body sway while walking were measured. The relationship between muscle strength asymmetry for each muscle and body sway while walking was evaluated using Pearson's correlation coefficient. Regarding the muscles recognized to have significant correlation with body sway, the asymmetry cutoff value causing an increased sway was calculated. Toe grip strength asymmetry was significantly correlated with body sway. Toe grip strength asymmetry causing an increased body sway had a cutoff value of 23.5%. Our findings suggest toe grip strength asymmetry may be a target for improving gait stability.

Femoral bone structure in Otsuka Long-Evans Tokushima Fatty rats.

OBJECTIVES: Type 2 diabetes mellitus (T2DM) increases fracture risk despite normal to high levels of bone mineral density. Bone quality is known to affect bone fragility in T2DM. The aim of this study was to clarify the trabecular bone microstructure and cortical bone geometry of the femur in T2DM model rats. METHODS: Five-week-old Otsuka Long-Evans Tokushima Fatty (OLETF; n = 5) and Long-Evans Tokushima Otsuka (LETO; n = 5) rats were used. At the age of 18 months, femurs were scanned with micro-computed tomography, and trabecular bone microstructure and cortical bone geometry were analyzed. RESULTS: Trabecular bone microstructure and cortical bone geometry deteriorated in the femur in OLETF rats. Compared with in LETO rats, in OLETF rats, bone volume fraction, trabecular number and connectivity density decreased, and trabecular space significantly increased. Moreover, in OLETF rats, cortical bone volume and section area decreased, and medullary volume significantly increased. CONCLUSIONS: Long-term T2DM leaded to deterioration in trabecular and cortical bone structure. Therefore, OLETF rats may serve as a useful animal model for investigating the relationship between T2DM and bone quality.

Tidal volume and diaphragm muscle activity in rats with cervical spinal cord injury.

[Purpose] The purpose of this study was to make an experimental model of cervical spinal cord injury (CSCI) using Wistar rats, in order to analyze the influence of CSCI on the respiratory function. [Subjects] Thirty-two male 12-week-old Wistar rats were used. [Methods] The CSCI was made at the levels from C3 to C7, and we performed pneumotachography and electromyography (EMG) on the diaphragm. Computed tomography was used to determine the level of spinal cord damage. [Results] After the operation, the tidal volume of the rats with a C3 level injury decreased to approximately 22.3% of its pre-injury value. In addition, in the same rats, the diaphragmatic electromyogram activity decreased remarkably. Compared with before CSCI, the tidal volume decreased to 78.6% of its pre-injury value in CSCI at the C5 level, and it decreased to 94.1% of its pre-injury value in CSCI at the C7 level. [Conclusion] In the rats that sustained a CSCI in this study, the group of respiratory muscles that receive innervation from the thoracic spinal cord was paralyzed. Therefore, the EMG signal of the diaphragm increased. These results demonstrate that there is a relationship between respiratory function and the level of CSCI.

ß-Carotene Increases Muscle Mass and Hypertrophy in the Soleus Muscle in Mice.

Supplements and naturally occurring nutraceuticals effective for maintenance or enhancement of skeletal muscle mass are expected to contribute to prevention of decreased mobility and increased risk of developing metabolic diseases. However, information about available food components remains widely unavailable. In the present study, we investigated the effects of dietary ß-carotene on the quantity and quality of skeletal muscle under physiological conditions. Male ddY mice (8 wk old) were orally administered ß-carotene (0.5 mg once daily) for 14 d. Dietary ß-carotene had no influence on body weight, but increased the soleus muscle/body weight ratio. The cross-sectional area (CSA) in muscle fibers of the soleus muscle was increased, indicating that administration of ß-carotene induces muscle hypertrophy. In the soleus muscle of the ß-carotene-administered mice, twitch force tended to be increased (p=0.06) and tetanic force was significantly increased, whereas specific force (force per CSA) remained unchanged. Dietary ß-carotene increased the mRNA level of insulin-like growth factor 1 (Igf-1) as its splicing variant Igf-1ea, but had no influence on the liver Igf-1 mRNA level or serum IGF-1 level. ß-Carotene promoted protein synthesis in the soleus muscle and reduced levels of ubiquitin conjugates, but had no influence on the mRNA levels of two atrogenes, Atrogin-1 and Murf1. On the other hand, ß-carotene had no influence on the processing of the autophagy marker protein light chain 3. These results indicate that in mice, administration of ß-carotene increases mass and induces functional hypertrophy in the soleus muscle, perhaps by promoting IGF-1-mediated protein synthesis and by reducing ubiquitin-mediated protein degradation.

Evaluation of Rhodiola rosea supplementation on skeletal muscle damage and inflammation in runners following a competitive marathon.

Adaptogens modulate intracellular signaling and increase expression of heat shock protein 72 (HSP72). Rhodiola rosea (RR) is a medicinal plant with demonstrated adaptogenic properties. The purpose of this study was to measure the influence of RR supplementation on exercise-induced muscle damage, delayed onset of muscle soreness (DOMS), plasma cytokines, and extracellular HSP72 (eHSP72) in experienced runners completing a marathon. Experienced marathon runners were randomized to RR (n=24, 6 female, 18 male) or placebo (n=24, 7 female, 17 male) groups and under double-blinded conditions ingested 600mg/day RR extract or placebo for 30days prior to, the day of, and seven days post-marathon. Blood samples were collected, and vertical jump and DOMS assessed the day before, 15min post- and 1.5h post-marathon. DOMS was also assessed for seven days post-marathon. Marathon race performance did not differ between RR and placebo groups (3.87±0.12h and 3.93±0.12h, respectively, p=0.722). Vertical jump decreased post-marathon (time effect, p<0.001) with no difference between groups (interaction effect, p=0.673). Post-marathon DOMS increased significantly (p<0.001) but the pattern of change did not differ between groups (p=0.700). Myoglobin (Mb), creatine phosphokinase (CPK), aspartate aminotransferase (AST), alanine aminotransferase (ALT), interleukin (IL)-6, IL-8, IL-10, monocyte chemotactic protein-1 (MCP-1), granulocyte-colony-stimulating factor (G-CSF), C-reactive protein (CRP), and eHSP72 all increased post-marathon (all p<0.001), with no group differences over time (all p>0.300). In conclusion, RR supplementation (600mg/day) for 30days before running a marathon did not attenuate the post-marathon decrease in muscle function, or increases in muscle damage, DOMS, eHSP72, or plasma cytokines in experienced runners.

The effects of hypoventilation disorder on physiological and biochemical properties of the hindlimb muscles.

The purpose of this study was to determine the physiological and biochemical properties of hindlimb muscles after hypoventilation (HPO) induced by bilateral phrenic nerve denervation. Male Wistar rats (10 weeks-old) underwent HPO by the phrenic nerve denervation at the cervical level or sham surgery. Analyses were performed 4, 8, and 12 weeks after the surgery. The myosin heavy chain (MHC) isoform profile and in vitro isometric contractile properties of the soleus (SOL) and extensor digitrum longus muscles (EDL) were analyzed. From the postoperative period, HPO induced characteristic changes in SpO2 such as hypoventilation disorder. After 12 weeks, significant increases in MHC1 and significant decreases in MHC2a were observed in the MHC isoform composition in SOL. Moreover, significant increases in MHC2a and significant decreases in MHC2b were also observed in the MHC isoform composition in EDL muscles in the HPO compared with sham (SHM) group. In our study, the tidal volume after unilateral phrenic nerve denervation decreased by approximately 12%, and that after bilateral phrenic nerve denervation decreased by approximately 35%. We concluded that the reduction in behavioral activity levels in the HPO group may have resulted in changes of the peripheral skeletal muscles as a result of disuse atrophy.

The relationship between skeletal muscle oxygenation and systemic oxygen uptake during exercise in subjects with COPD: a preliminary study.

BACKGROUND: Muscle oxygenation correlates with systemic oxygen uptake (V(O2)) in normal subjects; however, whether this relationship exists in COPD patients remains unclear. The purpose of this study was to investigate the influence of skeletal muscle oxygenation on V(O2) during exercise in patients with COPD. METHODS: Eight subjects performed an incremental cycle ergometer exercise test. We measured ventilation and pulmonary gas exchange with a metabolic measurement system. We also continuously monitored S(pO2), and measured tissue oxygen saturation (S(tO2)) in the vastus lateralis with continuous-wave near-infrared spectroscopy. We calculated the muscle oxygen extraction rate (MOER) based on S(pO2) and S(tO2). In addition, we calculated Pearson correlation coefficients to examine the relationships between the V(O2) obtained during exercise testing and the mean values of S(pO2), S(tO2), heart rate (HR), and MOER for each 30-second interval of the tests. Finally, we analyzed the relationships between the peak V(O2) and the slopes of HR/V(O2), S(pO2)/V(O2), S(tO2)/V(O2), and MOER/V(O2). RESULTS: With the increasing exercise intensity, many subjects showed a gradual decrease in S(tO2) and S(pO2), but a gradual increase in HR and MOER. V(O2) was negatively correlated with S(tO2) and S(pO2), and was positively correlated with HR and MOER. However, peak V(O2) was not correlated with any of the slopes. CONCLUSIONS: V(O2) is highly influenced by oxygen utilization in exercising muscles, as well as by blood oxygenation levels and cardiac function. However, the impact of skeletal muscle utilization during exercise on peak V(O2) varied greatly among the subjects.

Age-related changes in contraction and relaxation of rat diaphragm.

Age-related changes of physiological and biochemical properties were examined in the diaphragm muscle, which has particularly high activation compared to that of other skeletal muscles. The diaphragm from 10-week-, 50-week- and 100-week-old male Wistar rats were used to measure in vitro isometric contractile properties, sarcoplasmic reticulum (SR) Ca2+-ATPase activity, and myosin heavy chain (MHC) isoform composition. Although there were no significant differences in specific twitch tension of the diaphragm among the groups, there was significant reduction in specific tetanic tension in the 50-week to 100-week groups. The contraction time and 1/2 relaxation time of twitch contraction extended with aging, and significant differences were found between 10-week-old and 100-week-old diaphragms. Regarding the activity of SR Ca2+-ATPase, the pattern of age-related change was similar to that in the 1/2 relaxation time and there was a significant difference between 10-week-old and 100-week-old diaphragms. There was a significant increase in the relative composition of the MHC I isoform in 100-week-diaphragms compared to that in 10-week-old diaphragms and a concomitant decrease in the relative composition of fast myosin was noted. These findings demonstrated that older diaphragms have slower contraction and relaxation speeds, and these alterations were attributed to changes in SR Ca2+-ATPase activity and MHC isoform composition.