Gender muscle recovery during isokinetic exercise

The purpose of this study was to examine the effect of two between set rest intervals (RI) on isokinetic knee extension peak torque (PT) produced by sedentary women and men. Seventeen young women (27.18 ± 4.05 yrs) and 16 young men (26.75 ± 4.73 yrs) performed 3 sets of 10 unilateral isokinetic knee extension at 60° and 180°/s. The RI between sets was 60 and 120 s, counterbalanced across 2 testing days. Statistical evaluation of the data was performed using a 3-way mixed factor ANOVA (gender x rest interval x sets). Males and females exhibited decreases (p<0.05) in PT with 120 s RI at 60°/s. There was no significant decline in PT in the female group during both RI at 180°/s. Men showed a significant decrease in PT only with 60 s RI. Young women and men require more than 120 s of RI to recover full PT at 60°/s. However, full quadriceps's muscle strength recovery can be attained with a 60 and 120 s at 180°/s in women, but in men only with a 120 s at the same velocity.     

Dynamic joint forces during knee isokinetic exercise

This study analyzed forces in the tibiofemoral and patellofemoral joints during isokinetic exercise using an analytical biomechanical model. The results show that isokinetic exercise can produce large loads on these joints, especially during extension exercises. The tibiofemoral compressive force (4.0 body weight) is approximately equal to that obtained during walking but it occurs at 55 degrees of knee flexion. Anterior shear forces (resisting force to anterior drawer) exist during extension exercise at less than 40 degrees of knee flexion, with a maximum of 0.3 body weight. Posterior shear forces (resisting force to posterior drawer) exist during extension exercise at knee joint angles greater than 40 degrees and during the flexion portion of isokinetic exercise. The maximum posterior shear force is 1.7 body weight. The patellofemoral joint can encounter loads as high as 5.1 body weight which are 10 times higher than during straight leg raises. These results suggest that isokinetic exercise should be used cautiously in patients with knee lesions.     

Antagonist muscle coactivation during isokinetic knee extension

The aim of the present study was to quantify the amount of antagonist coactivation and the resultant moment of force generated by the hamstring muscles during maximal quadriceps contraction in slow isokinetic knee extension. The net joint moment at the knee joint and electromyographic (EMG) signals of the vastus medialis, vastus lateralis, rectus femoris muscles (quadriceps) and the biceps femoris caput longum and semitendinosus muscles (hamstrings) were obtained in 16 male subjects during maximal isokinetic knee joint extension (KinCom, ROM 90-10 degrees, 30 degrees x s(-1)). Two types of extension were performed: [1] maximal concentric quadriceps contractions and [2] maximal eccentric hamstring contractions Hamstring antagonist EMG in [1] were converted into antagonist moment based on the EMG-moment relationships determined in [2] and vice versa. Since antagonist muscle coactivation was present in both [1] and [2] a set of related equations was constructed to yield the moment/EMG relationships for the hamstring and quadriceps muscles, respectively. The equations were solved separately for every 0.05 degrees knee joint angle in the 90-10 degrees range of excursion (0 degrees = full extension) ensuring that the specificity of muscle length and internal muscle lever arms were incorporated into the moment/EMG relationships established. Substantial hamstring coactivation was observed during quadriceps agonist contraction. This resulted in a constant level of antagonist hamstring moment of about 30 Nm throughout the range of motion. In the range of 30-10 degrees from full knee extension this antagonist hamstring moment corresponded to 30-75% of the measured knee extensor moment. The level of antagonist coactivation was 3-fold higher for the lateral (Bfcl) compared to medial (ST) hamstring muscles The amount of EMG crosstalk between agonist-antagonist muscle pairs was negligible (Rxy2<0.02-0.06). The present data show that substantial antagonist coactivation of the hamstring muscles may be present during slow isokinetic knee extension. In consequence substantial antagonist flexor moments are generated. The antagonist hamstring moments potentially counteract the anterior tibial shear and excessive internal tibial rotation induced by the contractile forces of the quadriceps near full knee extension. In doing so the hamstring coactivation is suggested to assist the mechanical and neurosensory functions of the anterior cruciate ligament (ACL).     

Tibiofemoral joint forces during isokinetic knee extension

Using a Cybex II, eight healthy male subjects performed isokinetic knee extensions at two different speeds (30 and 180 deg/sec) and two different positions of the resistance pad (proximal and distal). A sagittal plane, biomechanical model was used for calculating the magnitude of the tibiofemoral joint compressive and shear forces. The magnitude of isokinetic knee extending moments was found to be significantly lower with the resistance pad placed proximally on the leg instead of distally. The tibiofemoral compressive force was of the same magnitude as the patellar tendon force, with a maximum of 6300 N or close to 9 times body weight (BW). The tibiofemoral shear force changed direction from being negative (tibia tends to move posteriorly in relation to femur) to a positive magnitude of about 700 N or close to 1 BW, indicating that high forces arise in the ACL when the knee is extended more than 60 degrees. The anteriorly directed shear force was lowered considerably by locating the resistance pad to a proximal position on the leg. This model may be used when it is desirable to control stress on the ACL, e.g., in the rehabilitative period after ACL repairs or reconstructions.     

Effects of active vs. passive recovery on repeated rugby-specific exercises

The aim of this study was to determine the effects of active vs. passive recovery on performance of a rugby-specific intermittent test in rugby union players. Seven male rugby players (20.6 ± 0.5 yrs; 181.9 ± 10.0 cm; 94.5 ± 12.8 kg) performed in random order, over two separate sessions, a specific repeated-sprint rugby test, the Narbonne test (6 × 4 consecutive actions: 1, scrummaging; 2, agility sprinting; 3, tackling; 4, straight sprinting) with 30 s of passive or active recovery (running at 50% of maximal aerobic speed). The Narbonne tests were completed before (pre-test) and after (post-test) a 30-min rugby match. During the Narbonne test, scrum forces, agility and sprint times, heart rate and rate of perceived exertion were measured. Scrum forces were lower in active (74.9 ± 13.4 kg) than in passive recovery (90.4 ± 20.9 kg), only during the post-test (p < 0.05). Fatigue index (%) (p < 0.05) and total sprint time (s) (p < 0.01) were significantly greater in active than in passive recovery, both during the pre-test (11.5 ± 5.7% vs. 6.7 ± 4.5% and 18.1 ± 1.3 s vs. 16.9 ± 0.9 s) and the post-test (7.3 ± 3.3% vs. 4.3 ± 1.5% and 18.3 ± 1.6 s vs. 16.9 ± 1.1 s). Consequently, the results indicated that passive recovery enabled better performance during the Narbonne test. However, it is obviously impractical to suggest that players should stand still during and following repeated-sprint bouts: the players have to move to ensure they have taken an optimal position.     

Lumbar spine loading during half-squat exercises

Evaluation of the compressive load acting on the lumbar spine (L3-L4) during half-squat exercises executed with a barbell resting on the subject's shoulders was undertaken. The kinematics of the upper body segments of two male and two female subjects as well as the barbell were described using data obtained by means of an optoelectronic system (CoSTEL). L3-L4 compressive load was calculated using a model of the anatomy of the trunk musculoskeletal system. Filtered surface electromyographic trunk flexor recordings from the obliquus externus and rectus abdominis and trunk extensor erectores spinae muscles as well as measurement of the ground reaction forces were also carried out for predicted result validation. During half-squat exercises with barbell loads in the range 0.8 to 1.6 times body weight the compressive loads on the L3-L4 segment vary between 6 and 10 times body weight. Erectores spinae contraction force was predicted to be between 30 and 50% of the relevant maximal isometric force. The magnitude of trunk flexion was found to be the variable which influenced most spinal compression load.     

Effects of active and passive recovery on lactate removal and subsequent isokinetic muscle function.

The effect of active and passive recovery on the removal of accumulated blood lactate and subsequent muscle function were tested using five male subjects. The experimental protocol consisted of two exercise sessions performed on a mechanical brake cycle ergometer at 150% VO2max for 60 seconds. Termination of the supramaximal work bouts were followed by a 20 minutes active recovery period cycling at 30% VO2max and a 20 minutes passive recovery period sitting quietly. Following the recovery modes, isokinetic measures of peak torque, total work output and fatigue were evaluated in the dominant quadricep muscle group. During the control test, exercise performance was limited to that of isokinetic evaluation. The order of the experimental and control tests were randomly assigned. Postexercise blood lactate levels prior to the isokinetic muscle test were 9.2 and 9.1 mM during the active and passive recovery conditions respectively. Blood lactate concentration during the control test was .4 mM prior to the isokinetic muscle test. The rate of blood lactate disappearance was significantly greater during active recovery (3.5 mM) when compared with passive recovery (7.2 mM). Blood lactate concentration during the control test was significantly lower (.4 mM) in comparison to both active and passive lactate concentrations prior to the isokinetic muscle test. Despite significant differences in blood lactate between active and passive recovery conditions, there was no difference in isokinetic measures of maximal strength, work output and muscle fatigue between recovery modes. Further indication that lactate is unrelated to muscle function was the nonsignificant finding in muscle function between the control and experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Benefits of HIV testing during military exercises

During U.S. Marine Corps Reserve summer 2-week active duty for training periods, 6,482 people were tested for human immunodeficiency virus (HIV). Testing at an initial exercise, Solar Flare, trained a cadre of contact teams to, in turn, train other personnel in phlebotomy and the HIV protocol at three other exercises (141 Navy Reserve and Inspector-Instructor hospital corpsmen were trained). Corpsmen could be trained with an indoctrination of 120 minutes and a mean of 15 phlebotomies. After 50 phlebotomies, the administration, identification, and labeling process plus phlebotomy could be completed in 90 seconds. HIV testing during military exercises is both good for training and cost-effective.     

Achilles tendon loading during weight bearing exercises

ObjectiveCompare the estimated Achilles tendon (AT) loading using a musculoskeletal model during commonly performed weight bearing therapeutic exercises.DesignControlled laboratory study.SettingUniversity biomechanics laboratory.ParticipantsEighteen healthy males (Age:22.1 ± 1.8 years, height:177.7 ± 8.4 cm, weight = 74.29 ± 11.3 kg).Main outcome measure(s)AT loading was estimated during eleven exercises: tandem, Romberg, and unilateral standing, unilateral and bilateral heel raising, unilateral and bilateral jump landing, squat, lunge, walking, and running. Kinematic and kinetic data were recorded at 180 Hz and 1800 Hz respectively. These data were then used in a musculoskeletal model to estimate force in the triceps surae. AT cross-sectional images were measured by ultrasound to determine AT stress. A repeated measure multivariate analysis of variance (α = 0.05) was used on AT loading variables.ResultsSquat and unilateral jump landing were the most different in AT stress. Peak AT stress variables were generally greater during more dynamic, unilateral exercises compared to more static, bilateral exercises.ConclusionsBilateral, more static exercises resulted in less AT loading and may serve as a progression during the rehabilitation compared to more dynamic, unilateral exercises.     

Subscapularis muscle activity during selected rehabilitation exercises

BACKGROUND: The upper and lower portions of the subscapularis muscle are independently innervated and activated. HYPOTHESIS: Upper and lower portions of the subscapularis muscle demonstrate different activation levels and require different exercises for rehabilitation. STUDY DESIGN: Controlled laboratory study. METHODS: Fifteen healthy subjects performed seven shoulder-strengthening exercises. Electromyographic data were collected from the latissimus dorsi, teres major, pectoralis major, infraspinatus, supraspinatus, and upper and lower subscapularis muscles. RESULTS: Upper subscapularis muscle activity was greater than lower subscapularis muscle activity for all exercises except for internal rotation with 0 degrees of humeral abduction. The push-up plus and diagonal exercises consistently stressed the upper and lower subscapularis muscles to the greatest extent. CONCLUSIONS: Humeral abduction was found to have a strong influence on the selective activation of the upper versus the lower subscapularis muscle and thus supported the design of different exercise continuums. In addition, the push-up plus and diagonal exercises were found to be superior to traditional internal rotation exercises for activating both functional portions of the subscapularis muscle. CLINICAL RELEVANCE: Our results showing that the upper and lower portions of the subscapularis muscle are functionally independent may affect training or rehabilitation protocols for the rotator cuff muscles.     

主动和被动运动对飞行员体液免疫功能的影响

目的:探讨主动运动和被动运动对飞行员血清几种免疫球蛋白和补体C3的影响。方法:42例健康男性歼击机飞行员随机分为主动运动和被动运动两组。测定试验前后血清免疫球蛋白G(IgG),免疫球蛋白A(IgA),免疫球蛋白M(IgM)和补体C3的含量。结果:两组试验后血清IgG、IgA、IgM和C3均升高,同试验前比较,有非常显著的差异(P<0.01)。结论:主动运动和被动运动均能增强机体体液免疫功能,提高机体防病、抗病能力。     

Serratus anterior muscle activity during selected rehabilitation exercises

The purpose of this study was to document the electromyographic activity and applied resistance associated with eight scapulohumeral exercises performed below shoulder height. We used this information to design a continuum of serratus anterior muscle exercises for progressive rehabilitation or training. Five muscles in 20 healthy subjects were studied with surface electrodes for the following exercises: shoulder extension, forward punch, serratus anterior punch, dynamic hug, scaption (with external rotation), press-up, push-up plus, and knee push-up plus. Electromyographic data were collected from the middle serratus anterior, upper and middle trapezius, and anterior and posterior deltoid muscles. Each exercise was partitioned into phases of increasing and decreasing force and analyzed for average and peak electromyographic amplitude. Resistance was provided by body weight, an elastic cord, or dumbbells. The serratus anterior punch, scaption, dynamic hug, knee push-up plus, and push-up plus exercises consistently elicited serratus anterior muscle activity greater than 20% maximal voluntary contraction. The exercises that maintained an upwardly rotated scapula while accentuating scapular protraction, such as the push-up plus and the newly designed dynamic hug, elicited the greatest electromyographic activity from the serratus anterior muscle.     

Passive versus active recovery during high-intensity intermittent exercises

PURPOSE: To compare the effects of passive versus active recovery on muscle oxygenation and on the time to exhaustion for high-intensity intermittent exercises. METHODS: Twelve male subjects performed a graded test and two intermittent exercises to exhaustion. The intermittent exercises (15 s) were alternated with recovery periods (15 s), which were either passive or active recovery at 40% of .VO2max. Oxyhemoglobin was evaluated by near-infrared spectroscopy during the two intermittent exercises. RESULTS: Time to exhaustion for intermittent exercise alternated with passive recovery (962 +/- 314 s) was significantly longer (P < 0.001) than with active recovery (427 +/- 118 s). The mean metabolic power during intermittent exercise alternated with passive recovery (48.9 +/- 4.9 mL.kg-1.min-1) was significantly lower (P < 0.001) than during intermittent exercise alternated with active recovery (52.6 +/- 4.6 mL.kg-1.min-1). The mean rate of decrease in oxyhemoglobin during intermittent exercises alternated with passive recovery (2.9 +/- 2.4%.s-1) was significantly slower (P < 0.001) than during intermittent exercises alternated with active recovery (7.8 +/- 3.4%.s-1), and both were negatively correlated with the times to exhaustion (r = 0.67, P < 0.05 and r = 0.81, P < 0.05, respectively). CONCLUSION: The longer time to exhaustion for intermittent exercise alternated with passive recovery could be linked to lower metabolic power. As intermittent exercise alternated with passive recovery is characterized by a slower decline in oxyhemoglobin than during intermittent exercise alternated with active recovery at 40% of .VO2max, it may also allow a higher reoxygenation of myoglobin and a higher phosphorylcreatine resynthesis, and thus contribute to a longer time to exhaustion.     

Assessment and interpretation of isokinetic muscle strength during growth and maturation

The majority of strength studies examining changes during growth and maturation have investigated isometric actions, which tell us little about the muscle under dynamic conditions. There are numerous methodological issues in the isokinetic testing of paediatric populations that require further investigation. However, several studies have indicated that children can be reliably assessed isokinetically using both concentric and eccentric actions. Most paediatric studies have examined the knee joint and more data are needed to elucidate the reliability of upper body isokinetic strength testing. The age- and sex-associated development of isokinetic strength is less well understood. Studies have indicated that isokinetic strength increases with age but the mechanisms associated with this increase require further investigation. Current data are also conflicting regarding the age at which sex differences become apparent in isokinetic strength. More work is needed to examine the influence of maturation on isokinetic strength development, but available data suggest that maturation is a non-significant contributory factor once stature and body mass are accounted for. Most studies have demonstrated a significant relationship between stature, body mass and isokinetic strength during growth and maturation. The importance that changes in body composition during growth have on isokinetic strength has been investigated using fat-free mass and muscle cross-sectional area. Data have shown that although fat-free mass and muscle cross-sectional area are important contributors to isokinetic strength, other unexplained factors also influence isokinetic strength development. Additional work needs to investigate possible qualitative changes in muscle during growth and maturation. More work is also needed to examine changes in eccentric strength with age and to investigate sex differences in upper body isokinetic strength. Future studies should preferably be longitudinal in nature and examine known covariates simultaneously using appropriate statistical techniques.     

Conditions of isokinetic knee flexion that enhance isokinetic knee extension

The results of two experiments are reported. The purpose of the initial investigation was to determine the effect of isokinetic knee flexion contraction intensity on subsequent knee extension contraction. Seven subjects performed ten isokinetic knee flexion-extension cycles at six isokinetic velocities under two antagonist contraction conditions. In the first condition, isokinetic knee flexion and extension were speed-matched, and, in the second condition, the high-speed condition, knee flexion was 7.85 rad.s-1 irrespective of knee extension velocity, which ranged from 0.52 to 7.85 rad.s-1. Significantly greater isokinetic knee extension measures were observed at low isokinetic velocities and were associated with the high-speed contraction condition. Enhancement of the knee extension contraction was in the initial work phase of the isokinetic contraction. The second experiment was conducted to determine whether the enhancement of the initial work phase could be associated, in part, with passive elastic qualities of the involved musculature. In this study the range of motion for the knee involved musculature. In this study the range of motion for the knee extension-flexion cycles was reduced from the previous 2.01 rad to 1.57 rad. Two isokinetic knee extension velocities were studied (1.57 and 7.85 rad.s-1) under five conditions: initiated from rest, initiated from isometric knee flexion MVC, and with preceding isokinetic knee flexion at 0.52, 4.19, and 7.85 rad.s-1. The hypothesis that knee extension contraction measures would not increase was supported. Based upon the results of the two experiments, it is suggested that the increases in knee extension contraction measures observed in the first experiment are at least partially mediated by the contribution to net torque by passive elastic musculotendinous elements. Further study of this phenomenon with the inclusion of electromyographic measures will allow determination of the presence and contribution of increased neural drive.     

Forces exerted during exercises on the uneven bars.

The purposes of this study were (1) to develop a technique to measure the force exerted on uneven bars during a gymnast's performance, and (2) to determine the magnitudes of the maximum forces exerted on the bars during normal use. Strain gages, a UV recorder, and motion-picture cameras were used to record the forces exerted against the bars and the motions with which they were associated. Three college gymnasts were used as subjects. Each performed several repetitions of an exercise sequence judged to result in the maximum loading of the bars she might produce under normal conditions. The maximum forces recorded were 3500 N (low bar) and 2140 N (high bar). These values were recorded during a sharp impact between the subject's thighs and the bar during the passage of the subject beneath the bar in a giant swing, respectively. Making due allowance for possible measurement error and for the estimated effects of the bars being used by gymnasts of greater mass than those in this study, it was concluded that bars should be designed to withstand repeated loads of at least 4205 N.     

Electromyographic activity and applied load during seated quadriceps exercises

PURPOSE: The aim of this study was to quantify and compare mean quadriceps muscle activity and applied load for eight seated quadriceps exercises using four types of resistance. METHODS: Using surface electromyography (EMG), the right rectus femoris (RF), vastus lateralis (VL), and vastus medialis oblique (VMO) muscles of 52 university students aged 23.5 +/- 3.4 yr (35 female and 17 male subjects) were examined during the exercises. Resistance devices included an ankle weight (78 N), blue Thera-Band tubing, a Cybex 340 isokinetic dynamometer, and an Inertial Exercise Trainer (IET). Electrogoniometer data were collected to determine the range of motion (ROM), angular velocity, and phase (concentric/eccentric) of exercise. Load cell data were analyzed to determine tubing and IET applied loads during exercise. A within-subjects criterion was used to improve intrasubject EMG reliability. All EMG values were normalized to a 100% maximum voluntary isometric contraction. Repeated measures ANOVAs with Bonferroni comparisons were used for statistical analysis. RESULTS: Within-subject effects of muscle and exercise were significant (P < 0.05) for both the concentric and eccentric muscle activity. The interaction effect of mean average EMG amplitude across exercises for the concentric phases of knee extension was significant (P = 0.001). No significant interactions were found for the eccentric phases of all seated quadriceps exercises. None of the exercises selectively isolated the VMO over the VL; however, the VMO/VL ratio was less (P < 0.05) during the concentric phases of the free weight and elastic tubing exercise when compared with the others. Eccentric phase VMO/VL ratios revealed that inertial resistance elicited greater muscle activity than other forms of resistance exercise. CONCLUSION: These findings suggest clinicians should consider biomechanical and resistance data when developing a strengthening program for the quadriceps muscle. Some seated quadriceps exercises may be more appropriate for certain rehabilitation goals than others.     

Anterior tibial translation during eccentric, isokinetic quadriceps work in healthy subjects

The effect of increasing isokinetic, eccentric quadriceps torques on sagittal translation of the tibia was examined in six healthy volunteers and compared to the translation at 20 degrees of knee flexion during a drawer test with 90 N force. The tibial translation increased in a linear fashion with a mean of 0.5 mm per 20% torque increase. In 20 degrees of knee flexion, 10% of eccentric quadriceps peak torque consumed 80% of the anterior tibial translation induced by the 90 N Lachman test while eccentric quadriceps peak torque utilized 100% of the translation at the same test. The in vivo relation between muscle force and tibial translation is of importance in the treatment of patients with injury to the cruciate ligaments. The results indicate that an already low eccentric quadriceps torque causes a tibial translation that reaches the limit of the passive knee joint displacement where strain is assumed to develop in the anterior cruciate ligament. Already low eccentric quadriceps torque levels may therefore be harmful during rehabilitation after anterior cruciate ligament surgery.     

Muscle strength and fatigue during isokinetic exercise in individuals with multiple sclerosis

PURPOSE: To compare muscle strength and muscle fatigue of the knee extensors and flexors in individuals with multiple sclerosis (MS) and non-MS control subjects and to evaluate the reliability of muscle strength and muscle fatigue testing in these individuals. METHODS: Thirty individuals (13 women and 2 men for both MS and control groups), age (mean +/- SD) 38.8 +/- 10 for MS and 33.1 +/- 7.6 yr for controls, participated in this investigation. Peak torque was measured on two occasions separated by approximately 7 d at 30, 60, 90, 120, 180 degrees.s(-1) with 2 min of recovery between each bout. The nondominant leg was tested followed by the dominant leg after 10 min of recovery. Subjects then performed three bouts of 30 flexions and extensions of the dominant leg at 180 degrees.s(-1) with 1 min of recovery between bouts. RESULTS: The reliability of muscle torque was very high for individuals with MS (only 1 of 20 measurements with an ICC below 0.900). Total work was also highly reliable for MS, but the Fatigue Index (work during the last 15 contractions/work during the first 15 contractions) x 100 was not. Peak torque adjusted for age, body mass, and fat free mass (measured by whole body plethysmography; the Bod Pod; Life Measurement Instruments; Concord, CA) was significantly greater for controls than for MS for three of four lower body muscle groups tested. For the muscle fatigue test (3 bouts of 30 knee extensions and flexions at 180 degrees.s(-1)), the Fatigue Index was greater (less fatigue) for the knee extensors for controls than MS for the third bout. For flexion, the Fatigue Index was greater for controls than MS over the three bouts (group effect). Total work was significantly greater for controls than MS for the flexors (group effect) and approached significance for the extensors. CONCLUSIONS: Individuals with MS were weaker than controls when data were adjusted for age, body mass, and fat free mass. This latter finding (force relative to age and fat free mass) suggests that there is a reduced ability to activate muscle mass in MS and/or the muscle mass of individuals with MS is of lower quality (i.e., reduced force/unit muscle mass) than controls.     

Regional blood flow during isokinetic dynamometric tests after 14-day bed rest

Time-course variations in regional circulation during isometric and isokinetic loads of varying intensity were measured after 14-day head-down tilt. It was found that pulse blood filling of the leg decreased and its vascular response to the load varied. These findings suggest that the impairment of the strength-velocity properties of muscles after hypokinesia is associated not only with their morphological changes but also with their inadequate blood supply during loading.