Applied Physiology

Muscle strength and function rather than muscle mass in sarcopenia

Response: Muscle strength and function rather than muscle mass in sarcopenia

Muscle strength, size, and neuromuscular function before and during adolescence Abstract Purpose To compare measurements of muscle strength, size, and neuromuscular function among pre-adolescent and adolescent boys and girls with distinctly different strength capabilities. Methods Fifteen boys (mean age ± confidence interval: 13.0 ± 1.0 years) and 13 girls (12.9 ± 1.1 years) were categorized as low strength (LS, n = 14) or high strength (HS, n = 14) based on isometric maximal voluntary contraction strength of the leg extensors. Height (HT), seated height, and weight (WT) determined maturity offset, while percent body fat and fat-free mass (FFM) were estimated from skinfold measurements. Quadriceps femoris muscle cross-sectional area (CSA) was assessed from ultrasound images. Isometric ramp contractions of the leg extensors were performed while surface electromyographic amplitude (EMGRMS) and mechanomyographic amplitude (MMGRMS) were recorded for the vastus lateralis (VL). Neuromuscular efficiency from the EMG and MMG signals (NMEEMG and NMEMMG, respectively) and log-transformed EMG and MMG vs. torque relationships were also used to examine neuromuscular responses. Results HS was 99–117% stronger, 2.3–2.8  years older, 14.0–15.7 cm taller, 20.9–22.3 kg heavier, 2.3–2.4 years more biologically mature, and exhibited 39–43% greater CSA than LS (p ≤ 0.001). HS exhibited 74–81% higher NMEEMG than LS (p ≤ 0.022), while HS girls exhibited the highest NMEMMG (p ≤ 0.045). Even after scaling for HT, WT, CSA, and FFM, strength was still 36–90% greater for HS than LS (p ≤ 0.031). The MMGRMS patterns in the LS group displayed more type I motor unit characteristics. Conclusions Neuromuscular adaptations likely influence strength increases from pre-adolescence to adolescence, particularly when examining large, force-producing muscles and large strength differences explained by biological maturity, rather than simply age.

Comparison between eccentric and concentric resistance exercise training without equipment for changes in muscle strength and functional fitness of older adults Abstract Purpose The present study tested the hypothesis that resistance exercise training focusing on eccentric muscle contractions would improve muscle strength and functional physical fitness more than concentric contraction-focused resistance training in older adults. Methods Healthy older adults (65–84 years) were placed into eccentric (ECC; n = 9) or concentric training group (CON; n = 8). They performed 4–6 basic manual resistance exercises focusing on either eccentric or concentric muscle contractions once at a community centre and at least twice at home a week for 8 weeks. Muscle thickness of the quadriceps femoris (MT), knee extensor maximal voluntary isometric contraction strength (MVC), 30-second chair stand (CS), 3-metre timed up and go (TUG), 2-minute step (2MS), sit and reach (SR), and static balance with eyes open and closed (Bal-EC) were assessed before and 7 days after the last community centre session. Results Changes in MT (ECC: 21.6 ± 9.2% vs CON: 6.7 ± 7.1%), MVC (38.3 ± 22.6% vs 8.2 ± 8.4%), CS (51.0 ± 21.7% vs 34.6 ± 28.3%), TUG (16.7 ± 9.9% vs 6.3 ± 7.7%), 2MS (9.9 ± 6.0% vs 6.0 ± 7.3%) and Bal-EC (35.1 ± 6.7% vs 8.8 ± 16.2%) from baseline were greater (P < 0.05) for the ECC than the CON group. Conclusion These results show that the eccentric manual resistance exercise training was more effective for improving lower limb strength, mobility, and postural stability of older adults when compared with the concentric training. This suggests the significance of emphasising eccentric muscle contractions in movements to maintain and improve physical function.

Stretch–shortening cycle exercise produces acute and prolonged impairments on endurance performance: is the peripheral fatigue a single answer? Abstract Objective This study aimed to verify the acute and prolonged effects of stretch–shortening cycle exercise (SSC) on performance and neuromuscular function following a 4-km cycling time trial (4-km TT). Methods On separate days, individuals performed a 4-km TT without any previous exercise (CON), immediately (ACUTE) and 48 h after (PROL) SSC protocol (i.e., 100-drop jumps). Neuromuscular function was measured at baseline SSC (baseline), before (pre-TT) and after (post-TT) 4-km TT. Muscle soreness and inflammatory responses also were assessed. Results The endurance performance was impaired in both ACUTE (− 2.3 ± 1.8%) and PROL (− 1.8 ± 2.4%) compared with CON. The SSC protocol caused also an acute reduction in neuromuscular function, with a greater decrease in potentiated quadriceps twitch-force (Qtw.pot − 49 ± 16%) and voluntary activation (VA − 6.5 ± 7%) compared for CON and PROL at pre-TT. The neuromuscular function was fully recovered 48 h after SSC protocol. Muscle soreness and IL-10 were elevated only 48 h after SSC protocol. At post-TT, Qtw.pot remained lower in ACUTE (− 52 ± 14%) compared to CON (− 29 ± 7%) and PROL (− 31 ± 16%). Conclusion These findings demonstrate that impairment in endurance performance induced by prior SSC protocol was mediated by two distinct mechanisms, where the acute impairment was related to an exacerbated degree of peripheral and central fatigue, and the prolonged impairment was due to elevated perceived muscle soreness.

Prior cycling exercise does not prevent endothelial dysfunction after resistance exercise Abstract Purpose Resistance exercise impairs endothelial function acutely. Therefore, it becomes important to devise an effective strategy for preventing acute endothelial dysfunction after resistance exercise. Herein, we tested the hypothesis that resistance exercise-induced temporal endothelial dysfunction is prevented by prior cycling. Methods Twelve young healthy subjects completed two randomized experimental trials: (1) resistance exercise only trial (RE trial), (2) resistance exercise with prior cycling trial (C + RE trial). Following baseline brachial artery flow-mediated dilation (FMD), the subjects maintained the supine position for 45 min in the RE trial; the subjects performed a 45 min of cycling (67.0 ± 1.7% HRmax) in the C + RE trial. After 45 min of resting or cycling, the subjects performed resistance exercise (69.7 ± 4.0 kg) at the same time points. Following the resistance exercise, they were asked to rest in the supine position for 60 min. Then FMD were repeated at 10, 30 and 60 min after the resistance exercise in both trials. Results The increased blood flow and shear rate after resistance exercise did not differ between trials, and these changes disappeared following resting in the supine position for 60 min. There was no significant interaction in %FMD responses. Both trials caused impairment in %FMD after the resistance exercise, and statistical significance was observed at 30 and 60 min after resistance exercise in the RE trial. Conclusion The present study revealed that cycling for 45 min prior to resistance exercise was not sufficient to prevent the acute endothelial dysfunction after resistance exercise.

RR interval signal quality of a heart rate monitor and an ECG Holter at rest and during exercise Abstract This study was designed to examine the RR interval signal qualities of a Holter device and a heart rate chest belt monitor at rest and during exercise. Ten healthy individuals completed five low- to high-intensity activities while simultaneously using the medilog® AR12plus  Holter monitor and the Polar H10 heart rate monitor. The RR interval signal quality was based on the quantification of the missing RR intervals and RR interval detection errors. Therefore, both measurement systems were compared against visual inspection of the raw electrocardiography signal. The missing and wrong R-wave peak detections were counted manually for both measurement systems. RR interval signal quality was defined as the relative number of correctly detected RR intervals. Overall, RR interval signal qualities of 94.6% and 99.6% were demonstrated for the medilog® AR12plus  and the Polar H10. During the high-intensity activities, the RR interval signal quality of the medilog® AR12plus  dropped to 89.8%, whereas the Polar H10 maintained a signal quality of 99.4%. The correlation between both systems was high (r = 0.997, p > 0.001). The excellent RR interval signal quality during low- to moderate-intensity activities in the medilog® AR12plus  and during low- to high-intensity activities in the Polar H10 demonstrates both measurement systems’ validity for the detection of RR intervals throughout a wide range of activities. A simple chest strap such as the Polar H10 might be recommended as the gold standard for RR interval assessments if intense activities with strong body movements are investigated.

Acute cardiopulmonary responses to strength training, high-intensity interval training and moderate-intensity continuous training Abstract Purpose Long-term effects of exercise training are well studied. Acute hemodynamic responses to various training modalities, in particularly strength training (ST), have only been described in a few studies. This study examines the acute responses to ST, high-intensity interval training (HIIT) and moderate-intensity continuous training (MCT). Methods Twelve young male subjects (age 23.4 ± 2.6 years; BMI 23.7 ± 1.5 kg/m2) performed an incremental exertion test and were randomized into HIIT (4 × 4-min intervals), MCT (continuous cycling) and ST (five body-weight exercises) which were matched for training duration. The cardiopulmonary (impedance cardiography, ergo-spirometry) and metabolic response were monitored. Results Similar peak blood lactate responses were observed after HIIT and ST (8.5 ± 2.6 and 8.1 ± 1.2 mmol/l, respectively; p = 0.83). The training impact time was 90.7 ± 8.5% for HIIT and 68.2 ± 8.5% for MCT (p < 0.0001). The mean cardiac output was significantly higher for HIIT compared to that of MCT and ST (23.2 ± 4.1 vs. 20.9 ± 2.9 vs. 12.9 ± 2.9 l/min, respectively; p < 0.0001). VO2max was twofold higher during HIIT compared to that observed during ST (2529 ± 310 vs. 1290 ± 156 ml; p = 0.0004). Among the components of ST, squats compared with push-ups resulted in different heart rate (111 ± 13.5 vs. 125 ± 15.7 bpm, respectively; p < 0.05) and stroke volume (125 ± 23.3 vs. 104 ± 19.8 ml, respectively; p < 0.05). Conclusions Despite an equal training duration and a similar acute metabolic response, large differences with regard to the training impact time and the cardiopulmonary response give evident. HIIT and MCT, but less ST, induced a sufficient cardiopulmonary response, which is important for the preventive effects of training; however, large differences in intensity were apparent for ST.

Do poles save energy during steep uphill walking? Abstract Purpose In trail running and in uphill races many athletes use poles. However, there are few data about pole walking on steep uphill. The aim of this study was to compare the energy expenditure during uphill walking with (PW) and without (W) poles at different slopes. Methods Fourteen mountain running athletes walked on a treadmill in two conditions (PW and W) for 5 min at seven different angles (10.1°, 15.5°, 19.8°, 25.4°, 29.8°, 35.5° and 38.9°). We measured cardiorespiratory parameters, blood lactate concentration (BLa) and rating of perceived exertion (RPE). Then, we calculated the vertical cost of transport (CoTvert). Using video analysis, we measured stride frequency (SF) and stride length (SL). Results Compared to W, CoTvert during PW was lower at 25.4°, 29.8° and 35.5° PW ( \( -\) 2.55 ± 3.97%; \( -\) 2.79 ± 3.88% and \( -\) 2.00 ± 3.41%, p < 0.05). RPE was significantly lower during PW at 15.5°, 19.8°, 29.8°, 35.5° and 38.9° ( \( -\) 14.4 ± 18.3%; \( -\) 16.2 ± 15.2%; \( -\) 16.6 ± 16.9%; \( -\) 17.9 ± 18.7% and \( -\) 18.5 ± 17.8%, p < 0.01). There was no effect of pole use on BLa. However, BLa was numerically lower with poles at every incline except for 10.1°. On average, SF for PW was lower than for W ( \( -\) 6.7 ± 5.8%, p = 0.006) and SL was longer in PW than in W (+ 8.6 ± 4.5%, p = 0.008). Conclusions PW on steep inclines was only slightly more economical than W, but the substantially lower RPE during PW suggests that poles may delay fatigue effects during a prolonged effort. We advocate for the use of poles during steep uphill walking, although the energetic savings are small.

A novel approach for establishing fitness standards for occupational task performance Abstract Purpose To identify strength and performance thresholds below which task performance is impaired. Methods A new weighted suit system was used to manipulate strength-to-body-weight ratio during the performance of simulated space explorations tasks. Statistical models were used to evaluate various measures of muscle strength and performance on their ability to predict the probability that subjects could complete the tasks in an acceptable amount of time. Thresholds were defined as the point of greatest change in probability per change in the predictor variable. For each task, median time was used to define the boundary between “acceptable” and “unacceptable” completion times. Results Fitness thresholds for four space explorations tasks were identified using 23 physiological input variables. Area under receiver operator characteristic curves varied from a low of 0.68 to a high of 0.92. Conclusion An experimental analog for altering strength-to-body weight combined with a probability-based statistical model for success was suitable for identifying thresholds for task performance below which tasks could either not be completed or time to completion was unacceptably high. These results provide data for strength recommendations for exploration mission ambulatory task performance. Furthermore, the approach can be used to identify thresholds for other areas where occupationally relevant tasks vary considerably.