Reactive oxygen species generation is not different during isometric and lengthening contractions of mouse muscle

Endogenous and Exogenous Antioxidants in Skeletal Muscle Fatigue Development during Exercise

Muscle fatigue is defined as a decrease in maximal force or power generated in response to contractile activity, and it is a risk factor for the development of musculoskeletal injuries. One of the many stressors imposed on skeletal muscle through exercise is the increased production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), which intensifies as a function of exercise intensity and duration. Exposure to ROS/RNS can affect Na⁺/K⁺-ATPase activity, intramyofibrillar calcium turnover and sensitivity, and actin-myosin kinetics to reduce muscle force production. On the other hand, low ROS/RNS concentrations can likely upregulate an array of cellular adaptative responses related to mitochondrial biogenesis, glucose transport and muscle hypertrophy. Consequently, growing evidence suggests that exogenous antioxidant supplementation might hamper exercise-engendering upregulation in the signaling pathways of mitogen-activated protein kinases (MAPKs), peroxisome-proliferator activated co-activator 1α (PGC-1α), or mammalian target of rapamycin (mTOR). Ultimately, both high (exercise-induced) and low (antioxidant intervention) ROS concentrations can trigger beneficial responses as long as they do not override the threshold range for redox balance. The mechanisms underlying the two faces of ROS/RNS in exercise, as well as the role of antioxidants in muscle fatigue, are presented in detail in this review.

Effect of intervertebral disc degeneration on the stomatognathic system function in adults

OBJECTIVE

To analyze the electromyographic activity (EMG) and thermographic patterns of the masseter and temporalis muscles and pressure of the orofacial tissues in individuals with intervertebral disc degeneration (IDD).

METHODS

This study had two distinct groups: with IDD (n = 16) and controls (n = 16). EMG at rest, protrusion, right and left laterality, and maximum voluntary contraction were evaluated. Tongue, orbicularis oris, and buccinator muscles pressures were measured by Iowa Oral Performance Instrument. The thermographic patterns were analyzed using infrared thermography.

RESULTS

Comparisons between groups showed significant differences regarding at rest [right (p = 0.05) and left (p = 0.05) masseter and right temporal (p = 0.05)], orofacial tissue pressure [tongue (p = 0.001), orbicularis oris (p = 0.01), and buccinator (p = 0.0001)], but no significant differences for the thermographic patterns.

CONCLUSION

IDD modifies the functionality of the craniomandibular complex, influencing the performance of the stomatognathic system.

Attenuation of eccentric exercise-induced muscle damage conferred by maximal isometric contractions: a mini review

Although, beneficial in determined contexts, eccentric exercise-induced muscle damage (EIMD) might be unwanted during training regimens, competitions and daily activities. There are a vast number of studies investigating strategies to attenuate EIMD response after damaging exercise bouts. Many of them consist of performing exercises that induce EIMD, consuming supplements or using equipment that are not accessible for most people. It appears that performing maximal isometric contractions (ISOs) 2–4 days prior to damaging bouts promotes significant attenuation of EIMD symptoms that are not related to muscle function. It has been shown that the volume of ISOs, muscle length in which they are performed, and interval between them and the damaging bout influence the magnitude of this protection. In addition, it appears that this protection is not long-lived, lasting no longer than 4 days. Although no particular mechanisms for these adaptations were identified, professionals should consider applying this non-damaging stimulus before submitting their patients to unaccustomed exercised. However, it seems not to be the best option for athletes or relatively trained individuals. Future, studies should focus on establishing if ISOs protect other populations (i.e., trained individuals) or muscle groups (i.e., knee extensors) against EIMD, as well as investigate different mechanisms for ISO-induced protection.

Mouse forepaw lumbrical muscles are resistant to age-related declines in force production

A progressive loss of skeletal muscle mass and force generating capacity occurs with aging. Mice are commonly used in the study of aging-associated changes in muscle size and strength, with most models of aging demonstrating 15-35% reductions in muscle mass, cross-sectional area (CSA), maximum isometric force production (Po) and specific force (sPo), which is Po/CSA. The lumbrical muscle of the mouse forepaw is exceptionally small, with corresponding short diffusion distances that make it ideal for in vitro pharmacological studies and measurements of contractile properties. However, the aging-associated changes in lumbrical function have not previously been reported. To address this, we tested the hypothesis that compared to adult (12month old) mice, the forepaw lumbrical muscles of old (30month old) mice exhibit aging-related declines in size and force production similar to those observed in larger limb muscles. We found that the forepaw lumbricals were composed exclusively of fibers with type II myosin heavy chain isoforms, and that the muscles accumulated connective tissue with aging. There were no differences in the number of fibers per whole-muscle cross-section or in muscle fiber CSA. The whole muscle CSA in old mice was increased by 17%, but the total CSA of all muscle fibers in a whole-muscle cross-section was not different. No difference in Po was observed, and while sPo normalized to total muscle CSA was decreased in old mice by 22%, normalizing Po by the total muscle fiber CSA resulted in no difference in sPo. Combined, these results indicate that forepaw lumbrical muscles from 30month old mice are largely protected from the aging-associated declines in size and force production that are typically observed in larger limb muscles.