Quadriceps muscle electromyography activity during physical activities and resistance exercise modes in younger and older adults

Translating In Vitro Models of Exercise in Human Muscle Cells: A Mitocentric View

Human skeletal muscle cell (HSkMC) models provide the opportunity to examine in vivo training-induced muscle-specific mitochondrial adaptations, additionally allowing for deeper interrogation into the effect of in vitro exercise models on myocellular mitochondrial quality and quantity. As such, this review will compare and contrast the effects of in vivo and in vitro models of exercise on mitochondrial adaptations in HSkMCs.

Myofibrillar Protein Synthesis and Acute Intracellular Signaling with Elastic Band Resistance Exercise in Young and Older Men

PURPOSE

Resistance exercise training (RET) attenuates age-related muscle and strength loss ("sarcopenia"). However, compared with machine-based RET, the efficacy of cost-effective, accessible elastic band RET (EB-RET) for muscle adaptive remodeling lacks supporting mechanistic evidence.

METHODS

Eight young (YM; 24 ± 4 yr) and eight older (OM; 68 ± 6 yr) untrained males consumed an oral stable isotope tracer (D 2 O) combined with serial vastus lateralis muscle biopsies to measure integrated myofibrillar protein synthesis (iMyoPS) and regulatory signaling over ~48 h before (habitual) and after an acute bout of EB-RET (6 × 12 repetitions at ~70% of one-repetition maximum). iMyoPS was determined via gas chromatography-pyrolysis-isotope ratio mass spectroscopy and regulatory signaling expression by immunoblot.

RESULTS

Habitual iMyoPS did not differ between YM and OM (1.62% ± 0.21% vs 1.43% ± 0.47%·d -1 , respectively, P = 0.128). There was a significant increase in iMyoPS after EB-RET in YM (2.23% ± 0.69%·d -1 , P = 0.02), but not OM (1.75% ± 0.54%·d -1 , P = 0.30). EB-RET increased the phosphorylation of key anabolic signaling proteins similarly in YM and OM at 1 h postexercise, including p-IRS-1 Ser636/639 , p-Akt Ser473 , p-4EBP-1 Thr37/46 , p-P70S6K Thr389 , and p-RPS6 Ser240/244 , whereas p-TSC2 Thr1462 and p-mTOR Ser2448 increased only in YM (all P < 0.05). There were no differences in the expression of amino acid transporters/sensors or proteolytic markers after EB-RET.

CONCLUSIONS

iMyoPS was elevated after EB-RET in YM but not OM. However, the increase in acute anabolic signaling with EB-RET was largely similar between groups. In conclusion, the capacity for EB-RET to stimulate iMyoPS may be impaired in older age. Further work may be necessary to optimize prescriptive programming in YM and OM.

Comparative Study of Muscle Hardness during Water-Walking and Land-Walking Using Ultrasound Real-Time Tissue Elastography in Healthy Young People

Compared with land-walking, water-walking is considered to be beneficial as a whole-body exercise because of the characteristics of water (buoyancy, viscosity, hydrostatic pressure, and water temperature). However, there are few reports on the effects of exercise in water on muscles, and there is no standard qualitative assessment method for muscle flexibility. Therefore, we used ultrasound real-time tissue elastography (RTE) to compare muscle hardness after water-walking and land-walking. Participants were 15 healthy young adult males (24.8 ± 2.3 years). The method consisted of land-walking and water-walking for 20 min on separate days. The strain ratio of the rectus femoris (RF) and medial head of gastrocnemius (MHGM) muscles were measured before and immediately after walking using RTE to evaluate muscle hardness. In water-walking, the strain ratio significantly decreased immediately after water-walking, with p < 0.01 for RF and p < 0.05 for MHGM, indicating a significant decrease in muscle hardness after water-walking. On the other hand, land-walking did not produce significant differences in RF and MHGM. Muscle hardness after aerobic exercise, as assessed by RTE, was not changed by land walking but was significantly decreased by water walking. The decrease in muscle hardness induced by water-walking was thought to be caused by the edema reduction effect produced by buoyancy and hydrostatic pressure.

The Influence of Motor Unit Number and Muscle Activation on Early Phase Rate of Torque Development in Younger and Older Men

This study examined the influence of muscle activation and motor unit number estimation (MUNE) on early phase voluntary rate of torque development (RTD) in younger (YM) and older (OM) men. Thirty-two YM (n = 17; Age = 22 yrs) and OM (n = 15; Age = 74 yrs) volunteered to participate in this study. Early phase RTD (first 50 ms of a rapid isometric contraction; RTD₅₀) and normalized surface electromyography (first 50 ms of muscle excitation; nEMG₅₀) were recorded from the right quadricep muscle group. MUNE was examined from the right vastus lateralis. Multiple linear regression analyses revealed that nEMG₅₀ had a significant effect on RTD₅₀ independent of age group (p ≤ 0.001). nEMG₅₀ had a significant effect on RTD₅₀ in the OM group (p = 0.037). MUNE had no effect on RTD₅₀ independent of age. Older adults may depend more on muscle activation at contraction onset of early phase RTD compared to younger adults.

Comparison of Muscle Activity and Ultrasound Response of Lower Extremity Muscles During Treadmill and Track Running

Purpose: The purpose of this study was to compare the changes in lower extremity muscle morphology and electromyography (EMG) signals during treadmill running (TR) and plastic track running (PR). Methods: A total of 10 healthy male runners aged 22.5±1.3 years, height: 175.5±4.5 cm; weight: 71.9±2.7 kg; BMI: 22.1±1.1 volunteered to participate in this study. Muscle morphology data were collected by a portable ultrasound scanner before and after running. Median frequency (MF), mean power frequency (MPF) and root mean square (RMS) were monitored during TR and PR. Results: The results indicated that muscle thickness and pennation angle have increased after running. The muscle thickness after PR showed significantly higher than TR in tested muscle except tibialis anterior (TA) and medial gastrocnemius (MG). In contrast, only the pennation angle of TA and lateral gastrocnemius (LG) after PR was significantly different from that after TR (P <0.001, P = 0.002). The most significant difference in the change rate of muscle thickness was found at TA. In addition, TA and MG showed significantly higher change rate of the pennation angle after TR than that after PR. Both of MF and MPF showed a downward trend after TR and PR. It could discover that the MF and MPF of LG during TR showed a significantly lower than that during PR both in two phases (P =0.001, P <0.001). However, in the last 5 minutes, MF and MPF of MQ during PR were smaller than that during PR (P = 0.001, P = 0.015). Furthermore, MF of RF during TR showed significantly different from that during PR (P = 0.017). From the point of RMS, in the first five minutes, the RMS of medical quadriceps (MQ), lateral quadriceps (LQ), hamstring muscles (HM) and MG during TR was significantly higher than that of PR (P <0.05). In addition, the RMS of all tested muscles after TR was significantly higher than after PR during the last 5 minutes (P <0.05). Conclusions: The current study indicated that TR and PR would cause different effects to lower extremity muscle morphology. In addition, the EMG signals based on running surfaces are also unconformity. Compared with the plastic track, the treadmill will bring more stimulation to the lower extremity muscles. The preliminary findings provide further insights into the rationality of runners’ choice of the running surface.

Impact of home-based squat training with two-depths on lower limb muscle parameters and physical functional tests in older adults

This study investigated the effect of home-based shallow and deep squat trainings on knee extension peak torque, muscle thickness, one-repetition maximum (1RM) leg press, and physical function in older individuals. Sixteen participants were randomly assigned to the shallow squat group (SS group; age, 71.0  ±  4.0 years) or deep squat group (DS group, age; 68.6  ± 3.6 years). Chairs of 40-cm height and chairs with a cushion of 20-cm height (60-cm in total) were used as the depth targets for squats, with participants instructed to sink until their hip touched the chair and cushion. Participants performed four sets of squats per day (35 repetitions per set), three days per week, for 12 weeks at their home. Knee extension peak torque, muscle thickness of quadriceps femoris (e.g., vastus lateralis, rectus femoris, and vastus intermedius), and physical function were measured at weeks 0 (baseline), 4, 8, and 12. Maximal isometric knee extension peak torque, muscle thickness, and walking speed did not change significantly over the 12-week training period in either group (P > 0.05). However, compared with the baseline, there was significant improvement in the results of 30-s sit-to-stand repetition tests after weeks 8 and 12 in both groups (P < 0.05). Additionally, 1RM leg press results were significantly improved after weeks 4 and 12 in the DS group, and weeks 4, 8, and 12 in the SS group (P < 0.05). Results indicate that home-based weight-bearing squat training improves lower limb function in older adults, as well as performance in physical functional tests related to activities of daily living. Moreover, such training benefits older adults regardless of whether squats are shallow or deep.