Intramuscular connective tissue content and mechanical properties: Influence of aging and physical activity in mice.

Aging is accompanied by morphological and mechanical changes to the intramuscular connective tissue (IMCT) of skeletal muscles, but whether physical exercise can influence these changes is debated. We investigated the effects of aging and exercise with high or low resistance on composition and mechanical properties of the IMCT, including direct measurements on isolated IMCT which has rarely been reported. Middle-aged (11 months, n = 24) and old (22 months, n = 18) C57BL/6 mice completed either high (HR) or low (LR) resistance voluntary wheel running or were sedentary (SED) for 10 weeks. Passive mechanical properties of the intact soleus and plantaris muscles and the isolated IMCT of the plantaris muscle were measured in vitro. IMCT thickness was measured on picrosirius red stained cross sections of the gastrocnemius and soleus muscle and for the gastrocnemius hydroxyproline content was quantified biochemically and advanced glycation end-products (AGEs) estimated by fluorometry. Mechanical stiffness, IMCT content and total AGEs were all elevated with aging in agreement with previous findings but were largely unaffected by training. Conclusion: IMCT accumulated with aging with a proportional increase in mechanical stiffness, but even the relatively high exercise volume achieved with voluntary wheel-running with or without resistance did not significantly influence these changes.

The Interplay between Multimorbidity, Physical Work Demands and Work Ability: Cross-Sectional Study among 12,879 Senior Workers.

Background: Aging increases the risk of chronic diseases, which can challenge the ability to work and thereby push senior workers out of the labour market. This study investigates the association between non-communicable diseases (NCDs) and work ability among workers ≥50 years (senior workers) with physically demanding and sedentary work, respectively. Methods: In the SeniorWorkingLife study, 12,879 senior workers replied to a questionnaire survey on work and health in 2018. Associations between the type and number of NCD and work ability (scale 0−10) were modelled using a general linear model adjusting for potential confounders and combined with model-assisted weights from national registers. Results: A higher number of NCD (multimorbidity) was progressively associated with a lower work ability (trend test, p-value < 0.001). Physical work influenced the association between the number of NCDs and work ability. For specific diseases, mental disorders, including burn-out syndrome (least square mean difference (LSMD): −1.46, 95% CI: −1.61 to −1.32) and stress ( LSMD: −1.18, 95% CI: −1.29 to −1.07), demonstrated a stronger association with a lower work ability compared with somatic diseases, such as back diseases (LSMD: −0.72, 95% CI: −0.80 to −0.64). Conclusions: Multimorbidity was progressively associated with a lower work ability in senior workers, especially among those with physical work.

Medio-Lateral Hamstring Muscle Activity in Unilateral vs. Bilateral Strength Exercises in Female Team Handball Players - A Cross-Sectional Study.

BACKGROUND: Reduced activation of the hamstring muscles and specifically the medial semitendinosus muscle (ST) has been shown to be a risk factor for non-contact anterior cruciate ligament (ACL) injury. Specific hamstring strength exercises may show high ST activity, however the effect of unilateral vs. bilateral exercise execution on ST activation remains unknown. PURPOSE: To investigate selected lower limb strengthening exercises performed either unilaterally or bilaterally to identify 1) which exercise elicited the highest hamstring activation, 2) which exercise elicited the highest ST activation, and 3) to examine if unilateral exercise execution altered the medio-lateral hamstring activation pattern. Furthermore, the kinematic characteristics of each specific exercise and execution modality were determined to reveal possible causes for differences in medio-lateral hamstring activation between the different exercise conditions. STUDY DESIGN: Cross-sectional study. METHODS: Single-session repeated measures were obtained in a randomized manner. Twenty-three female elite team handball players were recruited. Hamstring electromyographic (EMG) activity and 3D kinematics were obtained during selected lower limb exercises (hip thrust, kettlebell swing, Romanian deadlift). Hamstring EMG activity, normalized to maximal voluntary contraction (MVC) (nEMG), and inter-muscular activation difference between the ST and lateral hamstring biceps femoris (BF) were compared across exercises using two-way repeated measures ANOVA. RESULTS: Bilateral hip thrust demonstrated highest overall hamstring activity (68.9±16.6 %). Kettlebell swing (Δ13%-point, p<0.01) and Romanian deadlift (Δ20-24%-point, p<0.01) demonstrated greater ST-BF activation differences (Δ=ST-BF) in favor of ST compared to hip thrust (Δ2-7%). Positive correlations were observed between knee joint angle and ST activity in kettlebell swing and deadlift. CONCLUSION: Kettlebell swing, deadlift and hip thrust all produced high activation of the hamstring muscles. Kettlebell swing and both deadlift exercises were superior in activating ST over BF, favoring these exercises in the prevention of non-contact ACL injury in female athletes, which should be evaluated in future intervention studies. LEVEL OF EVIDENCE: 3.

Age-related myofiber atrophy in old mice is reversed by ten weeks voluntary high-resistance wheel running.

OBJECTIVE: Age-related loss of muscle mass and function can be attenuated in rodents with life-long voluntary wheel running with moderate resistance. The present study assessed if sarcopenia could be counteracted with ten weeks high intensity training. METHOD: Old (22-23 months) and middle-aged (11 months) mice were divided into three physical activity groups: Ten weeks of voluntary running in wheels with high (HR) or low resistance (LR), or no running wheel (SED). The wheel resistance was 0.5-1.5 g in the LR group and progressed from 5 g to 10 g in the HR group. Six, 8 and 5 old and 8, 9 and 9 middle-aged mice of the SED, LR and HR groups, respectively, were included in the analysis. Wheel activity was monitored throughout the intervention. Muscle mass of the tibialis anterior, gastrocnemius, soleus and plantaris muscles were measured post-mortem. Fiber type distribution and myofiber cross sectional areal (CSA) were quantified in the gastrocnemius and soleus muscles as well as total number of fibers in the soleus muscle. RESULTS: In the SED, the mass of all individual muscles was reduced in the old vs middle-aged (P < 0.001). In the training groups, the old mice ran significantly less, slower and for shorter bouts than the middle-aged throughout the intervention (P < 0.05). HR running increased the gastrocnemius and soleus muscle mass by 6% and 18% respectively in the old compared to SED. Fiber CSA was significantly reduced in the old SED mice, whereas fiber CSA in the old HR gastrocnemius and soleus muscles was comparable to the SED middle-aged. Fiber type shifted from 2b towards 2a in the gastrocnemius muscle of the trained old mice. HR running was more efficient than LR in maintaining muscle mass and myofiber size, and in shifting fiber types. In the middle-aged mice, similar effects were found, but less pronounced. Interestingly, fiber CSA was unaffected by running in the middle-aged. CONCLUSION: Ten weeks of HR running had a positive effect on muscle mass and morphology in both middle-aged and old mice. The old HR fiber CSA was greater than in old SED and comparable to the middle-aged, and the fibers shifted to a more oxidative composition (2b â†’ 2a). Albeit less pronounced, similar training effects were observed in the middle-aged mice despite running faster and longer than the old.