Fatigue-induced changes in knee-extensor torque complexity and muscle metabolic rate are dependent on joint angle

Purpose Joint angle is a significant determinant of neuromuscular and metabolic function. We tested the hypothesis that previously reported correlations between knee-extensor torque complexity and metabolic rate ($${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 ) would be conserved at reduced joint angles (i.e. shorter muscle lengths). Methods Eleven participants performed intermittent isometric knee-extensor contractions at 50% maximum voluntary torque for 30 min or until task failure (whichever occurred sooner) at joint angles of 30º, 60º and 90º of flexion (0º = extension). Torque and surface EMG were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) α. $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 was determined using near-infrared spectroscopy. Results Time to task failure/end increased as joint angle decreased (P < 0.001). Over time, complexity decreased at 90º and 60º (decreased ApEn, increased DFA α, both P < 0.001), but not 30º. $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 increased at all joint angles (P < 0.001), though the magnitude of this increase was lower at 30º compared to 60º and 90º (both P < 0.01). There were significant correlations between torque complexity and $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 at 90º (ApEn, r = − 0.60, P = 0.049) and 60º (ApEn, r = − 0.64, P = 0.035; DFA α, ρ = 0.68, P = 0.015). Conclusion The lack of correlation between $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and complexity at 30º was likely due to low relative task demands, given the similar kinetics of $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and torque complexity. An inverse correlation between $${\text{m}\dot{\text{V}}\text{O}}_{{2}}$$ m V ˙ O 2 and knee-extensor torque complexity occurs during high-intensity contractions at intermediate, but not short, muscle lengths.

Resistance training rejuvenates the mitochondrial methylome in aged human skeletal muscle

Resistance training (RT) alters skeletal muscle nuclear DNA methylation patterns (or the methylome). However, no study has examined if RT affects the mitochondrial DNA (mtDNA) methylome. Herein, ten older untrained males (65+/-7 years old) performed six weeks of full-body RT (twice weekly). Body composition and knee extensor torque were assessed prior to and 72 hours following the last RT session. Vastus lateralis (VL) biopsies were also obtained. VL DNA was subjected to reduced representation bisulfite sequencing providing excellent coverage across the ~16-kilobase mtDNA methylome (254 CpG sites). Various biochemical assays were also performed, and older male data were compared to younger trained males (22+/-2 years old, n=7). RT increased whole-body lean tissue mass (p=0.017), VL thickness (p=0.012), and knee extensor torque (p=0.029) in older males. RT also profoundly affected the mtDNA methylome in older males, as 63% (159/254) of the CpG sites demonstrated reduced methylation (p<0.05). Notably, several mtDNA sites presented a more youthful signature after RT in older males when comparisons were made to younger males. The 1.12 kilobase D-loop/control region on mtDNA, which regulates mtDNA replication and transcription, possessed enriched hypomethylation in older males following RT. Enhanced expression of mitochondrial H- and L-strand genes and increases in mitochondrial complex III and IV protein levels were also observed (p<0.05). This is the first study to show RT alters the mtDNA methylome in skeletal muscle. Observed methylome alterations may enhance mitochondrial transcription, and RT remarkably evokes mitochondrial methylome profiles to mimic a more youthful signature in older males.

The Effect of Cryotherapy on Proprioception and Knee Extensor Torque in Healthy Volunteers

Objectives: This study was done to investigate the influences of cryotherapy on the joint position sense (JPS) and extensor muscles torque of the knee. Methods: Forty healthy volunteers (20 men, 20 women; age range, 21 – 30 y) participated. Two cooling pads were applied to the knee and anterior thigh for 15 minutes at 4°C. The accuracy of the knee JPS was evaluated before and after cooling in two angles, including 45° and 60° flexion. Extensor muscles torque of the knee was obtained in two velocities of 30°/s and 120°/s. Results: The effect of time and the interaction between the group and time were not significant for both active and passive repositioning error tests of the knee joint angles (P ≥ 0.05). The knee extensor's muscle torque increased significantly during both velocities of 30°/s and 120°/s, immediately and 30 minutes after the cryotherapy in the experimental group (P ≤ 0.01). Cooling for 15 minutes made a higher knee extensor muscle torque and did not change the JPS. Conclusions: These findings should be considered for therapeutic programs that involve exercise immediately after a period of cryotherapy.

Modeling and Simulation of a Human Knee Exoskeleton's Assistive Strategies and Interaction

Exoskeletons are increasingly used in rehabilitation and daily life in patients with motor disorders after neurological injuries. In this paper, a realistic human knee exoskeleton model based on a physical system was generated, a human–machine system was created in a musculoskeletal modeling software, and human–machine interactions based on different assistive strategies were simulated. The developed human–machine system makes it possible to compute torques, muscle impulse, contact forces, and interactive forces involved in simulated movements. Assistive strategies modeled as a rotational actuator, a simple pendulum model, and a damped pendulum model were applied to the knee exoskeleton during simulated normal and fast gait. We found that the rotational actuator–based assistive controller could reduce the user's required physiological knee extensor torque and muscle impulse by a small amount, which suggests that joint rotational direction should be considered when developing an assistive strategy. Compared to the simple pendulum model, the damped pendulum model based controller made little difference during swing, but further decreased the user's required knee flexor torque during late stance. The trade-off that we identified between interaction forces and physiological torque, of which muscle impulse is the main contributor, should be considered when designing controllers for a physical exoskeleton system. Detailed information at joint and muscle levels provided in this human–machine system can contribute to the controller design optimization of assistive exoskeletons for rehabilitation and movement assistance.

Initial stages of hand osteoarthritis do not affect the extrinsic muscles of the hand: a cross-sectional study

The objective of this study was to verify whether women in the initial stages of hand osteoarthritis (HOA) already have impaired grip strength and flexor and extensor torque of the wrist compared to healthy women. It also aimed to correlate these variables with pain, stiffness, and function of the hand. Twenty-six women were divided into a control group [CG, n = 13; 56 (51–61) years old] and a hand osteoarthritis group [HOAG, n = 13; 58 (53–63) years old]. Grades II and III were included in the HOA group according to the criteria of Kellgren and Lawrence. All volunteers answered an initial assessment form, the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire and the Australian/Canadian Hand Osteoarthritis Index (AUSCAN). The grip strength and isometric wrist flexor and extensor torque were evaluated by a hydraulic dynamometer. Comparisons between groups used Student’s t test for independent samples and the Mann–Whitney test. Spearman's correlation was used to correlate grip strength and flexor and extensor wrist torque to the degree of disease and DASH and AUSCAN scores. There were no differences between the groups in grip strength or flexor and extensor torque values. In terms of the DASH and the AUSCAN, the HOA group had higher scores, indicating worse hand function. A strong negative correlation was found between grip strength and the degree of HOA (r = − 0.70, p = 0.008), and a moderate positive correlation was found between flexor torque and the degree of HOA (r = 0.53, p = 0.05). The pain (r = − 0.61, p = 0.02) and function (r = − 0.66, p = 0.01) sections of the AUSCAN correlated negatively with grip strength. Pain can be an important feature in the HOA rehabilitation process, as it can influence handgrip strength and function. It is important that rehabilitation is implemented as soon as possible to guarantee the maintenance of strength and function since with the severity of the disease, patients tend to have deficits in grip strength and function.

Effects of Unilateral Versus Bilateral Plyometric Training on Endurance Running Performance

The purpose of the study was to investigate the effects of an 11-week unilateral versus bilateral plyometric training intervention on maximal isometric voluntary (MVC) knee extensor torque, countermovement jump height (CMJ), running economy (RE) and 3-km time trial (TT) performance. Twenty-seven recreationally trained endurance runners (12 females and 15 males) were randomly assigned to one of three groups: unilateral plyometric training (UPT; n = 9), bilateral plyometric training (BPT; n = 9) and control (CON; n = 9). RE, VO2max, 3-km treadmill TT, isometric MVC (bilateral and unilateral) and CMJ (bilateral and unilateral) were measured prior to and after 11 weeks of training (UPT and BPT; volume equated, 20-40 minutes, 2-3 days/week). Separate two-way repeated measures ANOVAs were used to assess within and between group differences in RE, VO2max, 3-km TT, maximal isometric knee extensor torque and CMJ. Following 11 weeks of plyometric training there were significant improvements in RE (UPT 5.6%; BPT 4.9%, p < 0.01) and 3-km TT performance (UPT 2.4%; BPT 2.5%, p < 0.01) in addition to CMJ (UPT 12.5%; BPT 14.5%, p < 0.01) and maximal isometric knee extensor torque in the unilateral group (14.0%, p < 0.01). No significant differences in VO2max or anthropometric measures were detected (p > 0.05). No statistically significant differences between training interventions (p > 0.05) were detected in any measure. These data demonstrate that UPT and BPT result in similar improvements in RE and 3-km TT run performance in recreational distance runners.

Effects of Unilateral Versus Bilateral Plyometric Training on Endurance Running Performance

The purpose of the study was to investigate the effects of an 11-week unilateral versus bilateral plyometric training intervention on maximal isometric voluntary (MVC) knee extensor torque, countermovement jump height (CMJ), running economy (RE) and 3-km time trial (TT) performance. Twenty-seven recreationally trained endurance runners (12 females and 15 males) were randomly assigned to one of three groups: unilateral plyometric training (UPT; n = 9), bilateral plyometric training (BPT; n = 9) and control (CON; n = 9). RE, VO2max, 3-km treadmill TT, isometric MVC (bilateral and unilateral) and CMJ (bilateral and unilateral) were measured prior to and after 11 weeks of training (UPT and BPT; volume equated, 20-40 minutes, 2-3 days/week). Separate two-way repeated measures ANOVAs were used to assess within and between group differences in RE, VO2max, 3-km TT, maximal isometric knee extensor torque and CMJ. Following 11 weeks of plyometric training there were significant improvements in RE (UPT 5.6%; BPT 4.9%, p < 0.01) and 3-km TT performance (UPT 2.4%; BPT 2.5%, p < 0.01) in addition to CMJ (UPT 12.5%; BPT 14.5%, p < 0.01) and maximal isometric knee extensor torque in the unilateral group (14.0%, p < 0.01). No significant differences in VO2max or anthropometric measures were detected (p > 0.05). No statistically significant differences between training interventions (p > 0.05) were detected in any measure. These data demonstrate that UPT and BPT result in similar improvements in RE and 3-km TT run performance in recreational distance runners.