To clarify the relationship between cardiac myosin isozyme composition in running-trained rats and the sympathetic nervous system, we examined whether the sympathetic nervous system could contribute to the modulation of cardiac myosin isozyme in running-trained rats, using atenolol, a selective blocker of cardiac β₁ adrenegic receptor. Male Wistar strain rats (4 weeks old) were used, and divided into four groups: control sedentary (CS), control trained (CT), atenolol sedentary (AS), and atenolol trained (AT) . The AS and AT groups were treated with atenolol in drinking water (65 mg/kg/day) for 9 weeks. The CT and AT groups were trained by treadmill running (at 30 m/min for 1 h/day, 5 days/week), starting at 7 weeks old, for 6 weeks. At 13 weeks old, the hearts were excised. The left and right ventricular myosin isozymes were examined by electrophoresis on pyrophosphate gel. The results showed the followings: 1) In the CT and the AT groups, the citrate synthase activities of the plantaris muscle were increased by 26% compared with the CS group (p<0.05) . 2) In the CT group, the running training had no effect on the myosin isozyme composition, in both ventricular muscles. 3) In the AS group, the atenolol treatment resulted in a decrease in the proportion of the V1 myosin and in an increase in that of the V3 myosin. Therefore, the proportion of the β-myosin heavy chain (MHC) in both ventricles of the AS group showed a significant increase compared with the CS group (p<0.05) . 4) The AT group showed a marked increase in the proportion of the β-MHC in both ventricles, compared with that of the AS group, especially in the left ventricle (p<0.05) .
From the results presented here, we did not observe any effect of the sympathetic nervous system on cardiac myosin isozyme composition in the running-trained rats.
It is generally accepted that hemodynamic overload results in an increase in the proportion of β-MHC, and in contrast, the stimulation of the sympathetic nervous system induces an increase in α-MHC. Therefore, we speculated that the effect of running training on cardiac myosin isozyme composition was induced by the effects of both the sympathetic nervous system and hemodynamic overload. Consequently, running training had apparently no effect on myosin isozyme composition.

We examined the effect of running training on regional cardiac myosin isozyme composition in rats. Male Sprague-Dawley strain rats (4 weeks old) were used, and divided into two groups: sedentary control (C) and trained (T) groups. The T group was trained by treadmill running (40 m/min, 1h/day, 5 days/week, for 12 weeks) . At 16 weeks old, their hearts were excised. The left ventricle was separated into the subendocardium (Endo) and subepicardium (Epi) by dissecting the ventricle at the mid-wall. The ventricular myosin isozymes were examined by electrophoresis on pyrophosphate gel under non-dissociating conditions. The results showed the following: 1) The relative heart weight of the T group was significantly higher than the C group. 2) Left ventricular myosin isozyme composition showed a region-specific distribution in the C rats, and the proportion of V3 myosin or β-myosin heavy chain in the Endo was significantly higher than that of the Epi. However, the training had no effect on the cardiac myosin isozyme in either portion. 3) The activity of citrate synthase did not show transmural gradient in the ventricle of C animals. Training had no effect on the activities of either portion. 4) The activity of lactate dehydrogenase (LDH) showed transmural gradient in the ventricle of C rats. Training-induced changes in the activity of LDH were found in both portions, therefore, training abolished the transmural gradient in the activity of LDH, suggesting a corresponding redistribution of the myocardial work load.
These results indicate that running training might induce the redistribution of the myocardial work load, whereas the stimulation apparently has no effect on the regional distribution of cardiac myosin isozyme composition.

In this study, we performed isotemporal substitution analysis to examine potential associations of sedentary time and physical activity with mental health of Japanese office workers. This study employed a cross-sectional study design. We analyzed data on 108 Japanese office workers (mean age 46.4 ± 9.8 years; 64.8% women) in the study. Sedentary behavior (SB; ≤ 1.5 metabolic equivalents [METs]), light-intensity physical activity (LPA; 1.6–2.9 METs), and moderate-to-vigorous physical activity (MVPA; ≥ 3 METs) were measured with a triaxial accelerometer. Two kinds of self-administered questionnaires, the mental stress (K6) and work engagement (Utrecht Work Engagement Scale), were used to assess negative/positive mental health. A cut-off score of 5 or higher on the K6 was used to define persons with mental stress. Logistic and multiple regression analyses using an isotemporal substitution model was applied to demonstrate the association between replacing 30 min/d of SB with an equal amount of time spent on LPA or MVPA and mental stress and work engagement; the studied covariates were age, sex, body mass index, economic status, education, and overtime hours. The results showed that replacing SB with MVPA for 30 min/d was significantly decreased odds ratio (OR) of mental stress (OR = 0.38, 95% confidence interval 0.15–0.92), whereas the replacement was not associated with work engagement (B = 0.16, P = 0.38). In contrast, substitution of SB with LPA was not associated with mental stress and work engagement. These results indicate that substituting sedentary time with MVPA could be associated with mental stress of Japanese office workers.

Objective: There are many observational and clinical studies on pain treatment in farmers; however, little is known about the effects of interventions based only on randomized controlled trials (RCTs) on diseases of the musculoskeletal system or connective tissue (D-MSCT). This review aimed to summarize evidence on the effects of non-surgical interventions for pain relief and symptom improvement in farmers with D-MSCT.Materials and Methods: We searched seven databases, including MEDLINE, and three clinical trial registries, including the International Clinical Trials Registry Platform, from inception up to February 15, 2021, to identify studies that included at least one treatment group wherein nonsurgical interventions were applied. We focused on 1) pain relief and symptom improvement and 2) quality of life and improvement in physical fitness.Results: Four studies (three on low back pain and one on knee osteoarthritis) met all the inclusion criteria. Overall, the risk of bias was high, and meta-analysis could not be performed due to heterogeneity. However, a participatory ergonomic approach, exercise centered on strength training with a transtheoretical model, and/or a combination of both could be included in effective educational programs, at least in the short term, to prevent and/or reduce exacerbation of D-MSCT in farmers. Based on internal and external validity, we could postulate a future research agenda and a conceptual education model to prevent D-MSCT in farmers.Conclusion: Participatory ergonomic intervention, exercise centered on strength training, and/or a combination of both could be included for effective educational programs to prevent and reduce exacerbation of D-MSCT in farmers. High-quality RCTs with a less risk of bias will be implemented for many agricultural work types in various parts worldwide (especially developing countries and regions) during the COVID-19 pandemic.