EMG Analysis of Concurrent Activation Potentiation

Purpose: This study evaluated the effect of remote voluntary contractions (RVC) on concentric isokinetic knee extensor and flexor peak torque, rate of torque development, power, and work, the activation of the affected muscles, and gender differences therein. Methods: Eleven men and 12 women were evaluated with EMG and isokinetic dynamometry during knee extension and flexion tests in RVC and baseline (NO-RVC) test conditions. The RVC condition included jaw clenching, hand gripping, and the Valsalva maneuver. A two-way mixed ANOVA with repeated measures for test condition was used to evaluate the main effects for each isokinetic measure, as well as the EMG of the prime movers, their antagonist, and the muscles involved in the RVC, and the interaction between test condition and gender. Results: Significant interactions between test condition and gender indicate differences in response to RVC during knee extension tests for power and work (P ≤ 0.05) and for knee flexion tests for peak torque and power (P ≤ 0.05). All subjects produced higher peak torque and power during knee extension in the RVC condition (P ≤ 0.05). Men produced a higher rate of torque development and work during knee extension (P ≤ 0.05) and a higher peak torque and power during knee flexion in the RVC condition (P ≤ 0.05). Prime mover activation was greater in the RVC condition for most tests (P ≤ 0.05). Women demonstrated lower bilateral flexor digitorum superficialis activation than men during all tests in the RVC condition (P ≤ 0.05). Conclusions: RVC increased the performance of several outcome variables assessed, which coincides with the concomitant increase in EMG of the prime movers

Assessment of reliability in isokinetic testing among adolescent basketball players

Background. The reproducibility of day-to-day testing of isokinetic concentric and eccentric muscular actions among adolescent basketball players aged 14 to 16 years and relationships of mean within-subject variation in two isokinetic testing sessions with chronological age, biological maturation (estimated age at peak height velocity), training experience, body size, lower-body morphology, and initial strength performance were evaluated. Material and Methods. The sample included 27 basketball players who completed replicate test sessions of 5 repetitions of reciprocal concentric and eccentric knee extensions and flexions at 60 degrees s(-1). A randomly selected subsample of 8 players completed a third testing session to confirm reliability estimates. Results. Coefficients of variation (CV) between sessions 1 and 2 ranged from 8.1% to 17.4%, and intraclass coefficients (ICCs) ranged from 0.72 to 0.89. For sessions 1 and 3, CVs ranged from 3.9% to 6.0%, and ICCs ranged from 0.95 to 0.99. The initial level of strength of eccentric knee flexion (r=-0.43) and eccentric knee extension (r=-0.42) were correlated (P<0.05) with eccentric knee extension within-variation between two sessions. Training experience (r=-0.37, P<0.05) and initial values of concentric knee flexion (r=-0.62, P<0.01) were correlated with concentric knee flexion within-subject differences. Within-subject variation of eccentric knee extension was correlated (P<0.05) with chronologic age (r=0.41), estimated age at peak height velocity (r=-0.38), body size (r=0.41 to 0.47), and leg volume (r=0.39). Conclusions. Familiarization sessions may improve the reliability of concentric and eccentric knee isokinetic strength testing at 60 s(-1) in adolescent basketball players. Age, maturity status, and training experience of young athletes should be considered when testing knee isokinetic strength at 60 degrees s(-1)

Gearing effects of the patella (knee extensor muscle sesamoid) of the helmeted guineafowl during terrestrial locomotion

Human patellae (kneecaps) are thought to act as gears, altering the mechanical advantage of knee extensor muscles during running. Similar sesamoids have evolved in the knee extensor tendon independently in birds, but it is unknown if these also affect the mechanical advantage of knee extensors. Here, we examine the mechanics of the patellofemoral joint in the helmeted guineafowl Numida meleagris using a method based on muscle and tendon moment arms taken about the patella's rotation centre around the distal femur. Moment arms were estimated from a computer model representing hindlimb anatomy, using hip, knee and patellar kinematics acquired via marker‐based biplanar fluoroscopy from a subject running at 1.6 ms−1 on a treadmill. Our results support the inference that the patella of Numida does alter knee extensor leverage during running, but with a mechanical advantage generally greater than that seen in humans, implying relatively greater extension force but relatively lesser extension velocity

The effects of load and effort-matched concentric and eccentric knee extension training in recreational females

Purpose. The purpose of this study was to compare the effects of load and intensity of effort-matched concentric and eccentric knee extension training on isometric strength. Methods. Unilateral isometric torque was measured using a MedX knee extension after which eleven recreationally trained females performed both concentric-only (CONC) and eccentric-only (ECC) unilateral knee extension exercise once per week for 8 weeks. Participants performed a single set of both CONC and ECC exercise load matched at 80% of maximum isometric torque for each condition. All participants exercised to repetition maximum in both CONC and ECC conditions at a pace of ~3 s duration for each muscle action. This ensured that participants exercised to the same intensity of effort for both CONC and ECC training interventions. Results. Analyses revealed significant increases in isometric torque for both CONC (14.8%) and ECC (13.0%) conditions (p 0.05). Effect sizes are reported as 0.60 (CONC) and 0.53 (ECC). In addition, analyses revealed significantly greater mean total training volume for ECC compared with CONC conditions (15903 vs. 8091, respectively; p < 0.001). Conclusions. The present findings indicate that, when matched for intensity of effort, both CONC and ECC knee extension exercise can significantly improve strength to the same extent. This supports previous research that load and repetitions are not as important as intensity of effort in resistance exercise

The Cut-off Values for the Diagnosis of Hamstring Shortness and Related Factors

Background: Hamstrings are one of the most frequently evaluated muscle groups for flexibility in the lower extremity. Passive and active knee extension angle values are used as an indirect indicator of hamstring flexibility. However, the lack of consensus on the cut-off values leads to the use of inconsistent angle values in determining the hamstring tightness. Aims: To establish the normative and cut-off values of the passive and active knee extension angles for healthy young adults and to determine the associated factors including the quadriceps strength. Study Design: A cross-sectional study. Methods: A total of 123 volunteer university students, aged 18-24 years, who met the inclusion criteria were included in this study. Passive and active knee extension assessments of the subjects were performed. Subsequently, on the next day, both knee extensor concentric muscle strength of the participants was measured in the isokinetic system. The knee extension angles and the knee extensor strength were recorded as the mean values of the right and the left sides. Results: Passive knee extension angles of 17.1°±9.1° and 9.8°±5.7° and active knee extension angles of 17.8°±9.1° and 13.4°±6° were described as normative values in men and women, respectively. The cut-off values for the diagnosis of hamstring shortness were as follows: passive knee extension angle >32.2° for males and >19.2° for females and active knee extension angle >33.0° for males and >23.4° for females. A significant positive correlation was observed between knee extension angles and isokinetic knee extensor muscle strength in all participants. The knee extension angle and hamstring flexibility were not affected by dominance. Conclusion: The knee extension angles of healthy young people seem to be lower than the results currently reported in the literature. There s a positive correlation between knee extension angles and isokinetic knee extensor muscle strength

Muscle Damage following Maximal Eccentric Knee Extensions in Males and Females

Aim: To investigate whether there is a sex difference in exercise induced muscle damage. Materials and Method: Vastus Lateralis and patella tendon properties were measured in males and females using ultrasonography. During maximal voluntary eccentric knee extensions (12 reps x 6 sets), Vastus Lateralis fascicle lengthening and maximal voluntary eccentric knee extensions torque were recorded every 10° of knee joint angle (20–90°). Isometric torque, Creatine Kinase and muscle soreness were measured pre, post, 48, 96 and 168 hours post damage as markers of exercise induced muscle damage. Results: Patella tendon stiffness and Vastus Lateralis fascicle lengthening were significantly higher in males compared to females (p0.05). Creatine Kinase levels post exercise induced muscle damage were higher in males compared to females (p<0.05), and remained higher when maximal voluntary eccentric knee extension torque, relative to estimated quadriceps anatomical cross sectional area, was taken as a covariate (p<0.05). Conclusion: Based on isometric torque loss, there is no sex difference in exercise induced muscle damage. The higher Creatine Kinase in males could not be explained by differences in maximal voluntary eccentric knee extension torque, Vastus Lateralis fascicle lengthening and patella tendon stiffness. Further research is required to understand the significant sex differences in Creatine Kinase levels following exercise induced muscle damage

Skin toxicity after radiotherapy. About a case

A 60-year-old woman was admitted to the Department complaining of a slow growing mass in the right knee. Physical examination demonstrated a mass on the postero-lateral aspect of the right knee, which was not tender or mobile, however was rubbery and hard in consistency. Full flexion and extension was observed without any restriction of joint movement

Sagittal hip-knee coordination during a 45 degree cutting task

Background Hashemi et al. (2011) put forward a new theory of ACL injury mechanism, named the ‘hip extension knee flexion paradox’ that attempted to integrate itself with the most convincing findings in ACL research. This theory of mechanism stated that non-contact ACL injury would occur when the following four criteria are simultaneously met: 1) the tibial plateau has a posterior slope 2) the knee is near full extension upon application of a dynamic ground reaction force 3) activation of musculature about the knee is delayed and 4) hip extension and knee flexion occur concurrently. In their paper, Hashemi et al. (2011) also suggest that fatigue may play an important role in increasing the risk of non-contact ACL injury by delaying activation of musculature about the knee joint. Hip-knee coordination and the effect of fatigue on it, have however not previously been investigated. Purpose The purpose of this study was to quantify hip – knee coordination in the sagittal plane during a 45° cutting movement. Methods Nine female team sports players with experience at international or national level and no history of ACL injury were recruited. Written consent was obtained at the time of testing. Cutting was assessed under pre and post fatigue conditions, whilst motion capture data were collected for the lower limbs using QTM (Qualysis AB, Göteburg, Sweden). In each condition, ten successful 45° cuts were captured for the dominant leg. The fatiguing protocol comprised drop maximal vertical jumps and a multi-directional short sprint exercise. Hip and knee sagittal joint angles were extracted between the time of foot contact to 40 ms, the window in which ACL injury is believed to occur. A coordination pattern of 1) hip flexion – knee flexion, 2) hip extension – knee flexion, 3) hip extension – knee extension, 4) hip extension knee flexion was determined for each time point. The average time that each participant spent in each coordination pattern was calculated and the median coordination pattern was determined for each participant at each time point. Wilcoxon tests were executed in SPSS (IBM SPSS Version 22, Armonk, NY) to determine the effect of fatigue on the percentage time spent in hip extension – knee flexion and hip extension – knee extension. Results The average modal coordination pattern of the group, both pre- and post-fatigue, was to extend the hip and knee for the first 10 ms after foot contact. By 25 ms, all participants had changed coordination pattern to flex at the knee whilst continuing to extend at the hip. Both pre- and post-fatigue, a greater percentage of time (p&lt;0.05) was spent in hip extension – knee flexion than in hip extension – knee extension. No change was seen in the percentage time spent in hip extension – knee flexion after fatigue. Practical Applications Most players adopted a hip extension – knee extension pattern at foot contact before switching to hip extension – knee flexion. The initial observation of hip extension – knee extension was interesting as it represents stiffness at both the hip and knee joint, which has been suggested as high risk for non-contact ACL injury (Pollard et al., 2010). The latter coordination pattern has also been hypothesised as high risk for non-contact ACL injury and was dominant both pre- and post-fatigue. The absence of change in coordination patterns after fatigue suggests this risk factor was not accentuated as a result of a short duration fatiguing protocol in an elite, healthy population