Effects of isokinetic training of the knee extensors on high-intensity exercise performance and skeletal muscle buffering

Twenty-three subjects isokinetically trained the right and left quadriceps femoris, three times per week for 16 weeks; one group (n=13) trained at an angular velocity of 4.19 rad · s^–1 and a second group (n=10), at 1.05 rad · s^–1. A control group (n=10) performed no training. Isometric endurance time at 60% quadriceps maximum voluntary contraction (MVC), mean power output and work done (W) during all-out cycling, and the muscle buffer value (B) and carnosine concentration of biopsy samples from the vastus lateralis, were all assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of these variables (P < 0.05). No significant difference in either 60% MVC endurance time or impulse [(endurance time × force) at 60% MVC] was observed for any group after the 16 week period (P > 0.05). However, the post-training increase (9%) in W during high-intensity cycling was greater in the training group than in the control group (P=0.04). NeitherB nor carnosine concentration showed any significant change following training (P=0.56 andP=0.37, respectively). It is concluded that 16 weeks of isokinetic training of the knee extensors enables subjects to do more work during high-intensity cycling. Although the precise adaptations responsible for the improved performance have yet to be identified, they are unlikely to include an increase inB.     

Arthrogenic muscle response induced by an experimental knee joint effusion is mediated by pre- and post-synaptic spinal mechanisms

Knee joint effusion results in quadriceps inhibition and is accompanied by increased excitability in the soleus musculature. The purpose of this study was to determine if soleus arthrogenic muscle response is regulated by pre- or post-synaptic spinal mechanisms. Ten healthy adults (two females and eight males) were measured on two occasions. At the first session, subjects had their knee injected with 60 ml of saline and in the other session they did not. Pre- and post-synaptic spinal mechanisms were measured at baseline, immediately following a needle stick, immediately following a Xylocaine injection, and 25 and 45 min post-saline injection. A mixed effects model for repeated measures was used to analyze each dependent variable. The a priori alpha level was set a P≤0.05. The percentage of the unconditioned reflex amplitude for recurrent inhibition (P<0.0001) and reflex activation history (P<0.0001) significantly increased from baseline at 25 and 45 min post-effusion. Soleus arthrogenic muscle response seen following knee joint effusion is mediated by both pre- and post-synaptic mechanisms. In conclusion, the arthrogenic muscle response seen in the soleus musculature following joint effusion is regulated by both pre- and post-synaptic control mechanisms. Our data are the first step in understanding the neural networks involved in the patterned muscle response that occurs following joint effusion.     

Reduction in range of movement can increase maximum voluntary eccentric forces for the human knee extensor muscles

Using the KinCom 500H isokinetic dynamometer the first part of this study measured the characteristics of the force velocity relationship curve for the human knee extensors between -1.57 (eccentric) and 3.67 (concentric) rads x s(-1) (-90 and 210 degrees s(1)) for both legs in 4 subjects. A significant increase in force generation was seen in eccentric activity at 0.52 rads x s(-1) (30 degrees s(-1)) but not at 1.57 rads x s(-1) (90 degrees s(-1)) compared to maximum voluntary isometric force (P < 0.005). This increase was, however, lower than would be expected from the classical force-velocity relationship. The second part of the study examined whether restricting the range of movement was able to further increase the eccentric forces. In a further 6 subjects, the eccentric contractions were repeated during either an 80 degrees (15-95 degrees flexion) and a 50 degrees (45-95 degrees flexion) range of movement. Significant increases in force were seen over the shorter range of movement at 0.52 rads x s(-1) (30 degrees s(-1)) (P = 0.006) and 1.57 rads x s(-1) (90 degrees s(-1)) (P < 0.001).     

平衡性训练对膝关节内侧副韧带损伤患者膝关节功能恢复的效果研究

目的:研究平衡性训练对膝关节内侧副韧带(MCL)损伤患者膝关节功能恢复的效果。方法:选取2014年8月至2016年8月北京体育大学运动员膝关节MCL损伤患者112例为研究对象,根据随机数字表法将其分为对照组(n=56)与观察组(n=56)。对照组予以常规康复训练干预,观察组则在对照组的基础上加用平衡性训练干预,两组患者干预时间均为4周,分别比较两组干预前和干预4周后膝关节功能变化情况、疼痛程度、膝关节平衡能力以及生活质量的变化。结果:干预后两组患者Lysholm评分均较干预前升高,且观察组明显高于对照组,差异有统计学意义(P0.05)。干预后两组患者视觉模拟(VAS)评分均明显低于干预前,且观察组明显低于对照组,差异均有统计学意义(均P0.05)。干预后,两组患者总体稳定指数(OSI)、前后方向的稳定指数(APSI)、左右方向的稳定指数(MLSI)水平均低于干预前,且观察组患者OSI、APSI、MLSI水平均低于对照组,差异均有统计学意义(均P0.05)。观察组患者满意度较对照组明显升高,差异有统计学意义(P0.05)。结论:为膝关节MCL损伤患者实施平衡性训练能较好地改善其膝关节功能,并缓解疼痛,同时可帮助其提高膝关节的平衡能力,增加了满意度,适于推广。     

入伍新训中膝关节损伤的特点与防治研究

目的：通过对某部新入伍官兵训练中膝关节损伤发生原因、特点进行流行性病学调查和分析,为合理训练,预防损伤发生和治疗相关伤病提供指导依据。方法：对某部2013 年度450 名新入伍官兵的训练伤发病情况进行统计分析,重点分析膝关节损伤发生率、伤病类型和致伤原因,并对其严重者进行关节镜治疗,观察和分析术后随访效果。结果：某部新兵的训练伤发生率为20.0%。以关节急性扭伤最为多见,占81.1%。其中膝关节损伤共发生32 例,占训练伤发病率为7.1%,占训练伤发病率43.8%,其中膝关节周围肌肉损伤20 例、交叉韧带损伤1 例、半月板损伤9 例、侧副韧带损伤2 例。致伤率最高的前3 位科目是5000 米负重跑、跨越障碍训练、格斗训练,共27 例,占膝关节训练伤总数的84.4%。所有受伤患者中,12 例行手术治疗,20 例给予石膏、支具固定、休息等保守治疗。经随访所有患者均得到较好的功能恢复。结论：对于新兵膝关节训练伤预防工作非常重要,避免致残;关节镜手术技术的进步对于膝关节军事训练伤治疗有良好的效果。     

Electromyographic responses of erector spinae and lower limb’s muscles to dynamic postural perturbations in patients with adolescent idiopathic scoliosis

The aim of this study was to evaluate electromyographic (EMG) responses of erector spinae (ES) and lower limbs’ muscles to dynamic forward postural perturbation (FPP) and backward postural perturbation (BPP) in patients with adolescent idiopathic scoliosis (AIS) and in a healthy control group. Ten right thoracic AIS patients (Cobb = 21.6 ± 4.4°) and 10 control adolescents were studied. Using bipolar surface electrodes, EMG activities of ES muscle at T10 (ES_T10) and L3 (ES_L3) levels, biceps femoris (BF), gastrocnemius lateralis (G) and rectus femoris (RF) muscles in the right and the left sides during FPP and BPP were evaluated. Muscle responses were measured over a 1s time window after the onset of perturbation. In FPP test, the EMG responses of right ES_T10, ES_L3 and BF muscles in the scoliosis group were respectively about 1.40 (p = 0.035), 1.43 (p = 0.07) and 1.45 (p = 0.01) times greater than those in control group. Also, in BPP test, at right ES_L3 muscle of the scoliosis group the EMG activity was 1.64 times higher than that in the control group (p = 0.01). The scoliosis group during FPP displayed asymmetrical muscle responses in ES_T10 and BF muscles. This asymmetrical muscle activity in response to FPP is hypothesized to be a possible compensatory strategy rather than an inherent characteristic of scoliosis.     

Elevated gastrocnemius forces compensate for decreased hamstrings forces during the weight-acceptance phase of single-leg jump landing: implications for anterior cruciate ligament injury risk

Approximately 320,000 anterior cruciate ligament (ACL) injuries in the United States each year are non-contact injuries, with many occurring during a single-leg jump landing. To reduce ACL injury risk, one option is to improve muscle strength and/or the activation of muscles crossing the knee under elevated external loading. This study?s purpose was to characterize the relative force production of the muscles supporting the knee during the weight-acceptance (WA) phase of single-leg jump landing and investigate the gastrocnemii forces compared to the hamstrings forces. Amateur male Western Australian Rules Football players completed a single-leg jump landing protocol and six participants were randomly chosen for further modeling and simulation. A three-dimensional, 14-segment, 37 degree-of-freedom, 92 muscle-tendon actuated model was created for each participant in OpenSim. Computed muscle control was used to generate 12 muscle-driven simulations, 2 trials per participant, of the WA phase of single-leg jump landing. A one-way ANOVA and Tukey post-hoc analysis showed both the quadriceps and gastrocnemii muscle force estimates were significantly greater than the hamstrings (p<0.001). Elevated gastrocnemii forces corresponded with increased joint compression and lower ACL forces. The elevated quadriceps and gastrocnemii forces during landing may represent a generalized muscle strategy to increase knee joint stiffness, protecting the knee and ACL from external knee loading and injury risk. These results contribute to our understanding of how muscle?s function during single-leg jump landing and should serve as the foundation for novel muscle-targeted training intervention programs aimed to reduce ACL injuries in sport.     

Effects of isokinetic training of the knee extensors on isometric strength and peak power output during cycling

Isokinetic training of right and left quadriceps femoris was undertaken three times per week for 16 weeks. One group of subjects (n = 13) trained at an angular velocity of 4.19 rad.s-1 and a second group (n = 10) at 1.05 rad.s-1. A control group (n = 10) performed no training. Maximal voluntary contraction (MVC) of the quadriceps, and peak pedal velocity nu p,peak) and peak power output (Wpeak) during all-out cycling (against loads equivalent to 9, 10, 11, 12, 13 and 14% MVC) were assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of the performance variables (P > 0.05). No significant difference in MVC was observed for any group after the 16-week period (P = 0.167). The post-training increases in average Wpeak (7%) and nu p,peak (6%) during the cycle tests were each significantly different from the control group response (P = 0.018 and P = 0.008, respectively). It is concluded that 16 weeks of isokinetic strength training of the knee extensors is able to significantly improve nu p, peak and Wpeak during spring cycling, an activity which demands considerable involvement of the trained muscle group but with its own distinct pattern of coordination.     

Contributions of muscles to terminal-swing knee motions vary with walking speed

Many children with cerebral palsy walk with diminished knee extension during terminal swing, at speeds much slower than unimpaired children. Treatment of these gait abnormalities is challenging because the factors that extend the knee during normal walking, over a range of speeds, are not well understood. This study analyzed a series of three-dimensional, muscle-driven dynamic simulations to determine whether the relative contributions of individual muscles and other factors to angular motions of the swing-limb knee vary with walking speed. Simulations were developed that reproduced the measured gait dynamics of seven unimpaired children walking at self-selected, fast, slow, and very slow speeds (7 subjects×4 speeds=28 simulations). In mid-swing, muscles on the stance limb made the largest net contribution to extension of the swing-limb knee at all speeds examined. The stance-limb hip abductors, in particular, accelerated the pelvis upward, inducing reaction forces at the swing-limb hip that powerfully extended the knee. Velocity-related forces (i.e., Coriolis and centrifugal forces) also contributed to knee extension in mid-swing, though these contributions were diminished at slower speeds. In terminal swing, the hip flexors and other muscles on the swing-limb decelerated knee extension at the subjects’ self-selected, slow, and very slow speeds, but had only a minimal net effect on knee motions at the fastest speeds. Muscles on the stance limb helped brake knee extension at the subjects’ fastest speeds, but induced a net knee extension acceleration at the slowest speeds. These data—which show that the contributions of muscular and velocity-related forces to terminal-swing knee motions vary systematically with walking speed—emphasize the need for speed-matched control subjects when attempting to determine the causes of a patient's abnormal gait.     

Use of quantitative membrane proteomics identifies a novel role of mitochondria in healing injured muscles

Skeletal muscles are proficient at healing from a variety of injuries. Healing occurs in two phases, early and late phase. Early phase involves healing the injured sarcolemma and restricting the spread of damage to the injured myofiber. Late phase of healing occurs a few days postinjury and involves interaction of injured myofibers with regenerative and inflammatory cells. Of the two phases, cellular and molecular processes involved in the early phase of healing are poorly understood. We have implemented an improved sarcolemmal proteomics approach together with in vivo labeling of proteins with modified amino acids in mice to study acute changes in the sarcolemmal proteome in early phase of myofiber injury. We find that a notable early phase response to muscle injury is an increased association of mitochondria with the injured sarcolemma. Real-time imaging of live myofibers during injury demonstrated that the increased association of mitochondria with the injured sarcolemma involves translocation of mitochondria to the site of injury, a response that is lacking in cultured myoblasts. Inhibiting mitochondrial function at the time of injury inhibited healing of the injured myofibers. This identifies a novel role of mitochondria in the early phase of healing injured myofibers.