Influence of sports background on leg muscle coordination in vertical jumps

This study was planned to investigate the influence of sports background on leg muscle coordination during vertical jumps (concentric and drop jumps). Five different athlete groups were chosen as subjects: jumpers in athletics, swimmers, soccer players and poor and good vertical jumpers. Motor versatility was used as an additional inclusion criterion. Interest centred on the comparison of two different movement models: the jumping model (jumpers) and the kicking model (swimmers). The jumpers performed the most powerful vertical jumps. Proportional IEMG activity showed that their catapult innervation did not follow the proximo-distal model. The jumpers exemplified the stiffness innervation typical of power athletes. The swimmers turned out to be the poorest jumping group. Their agonist muscle coordination resembled more the simultaneous than sequential proximo-distal model. Furthermore, the agonist and antagonist muscles of both the thigh and shank showed co-contraction instead of reciprocal innervation. The simultaneous model adopted by all the leg muscles and a tendency to produce a new burst of activity at the end of the contact phase seem to be associated with the posture and stiffness demands of swimming performance. The soccer players showed an intermediate innervation, including a sequential flow of activity, but also a poor reciprocal function and a tendency to produce a new burst of activity at the end of the contact phase. The DDJ-type activity coordination of the poor and good vertical jumpers (Deep Drop Jump, Eloranta 1997b) most resembled the stereotypical proximo-distal flow of activity of the vertical jump (Bobbert and van Ingen Schenau 1988). The results suggest that prolonged training in a specific sport will cause the central nervous system (CNS) to program muscle coordination according to the demands of that sport. That learned skill-reflex (automatic skill program, Eloranta 1997b) of the CNS seems to interfere hierarchically in the performance program of another task. Therefore, it is reasonable to believe that human movement behavior is characterized by previously learned skill-reflexes.     

Mechanical efficiency during repetitive vertical jumping

The purpose of this study was to compare mechanical efficiency between repeated static jumps (SJ), countermovement jumps (CMJ), drop jumps from 75% of maximum CMJ jump height (75DJ) and drop jumps from 125% of maximum CMJ height (125DJ). Subjects included eight jump-trained males. All subjects completed 30 continuous repetitions in the SJ, CMJ, 75DJ, and 125DJ. Oxygen consumption, peak force and center of mass displacement for each repetition during the four jumping patterns were measured. ME was calculated from a combination of force-time curves, displacement-time curves and lactate-corrected oxygen consumption values. In addition, muscle activity was recorded from the vastus medialis, vastus lateralis and biceps femoris using surface electromyography (EMG). 125DJ and 75DJ resulted in significantly (P ≤ 0.05) greater ME in comparison to CMJ and SJ. CMJ resulted in significantly greater ME in comparison to SJ. In addition, braking phase muscle activity was significantly greater in 125DJ and 75DJ in comparison to CMJ. Negative work was significantly different between 125DJ, 75DJ and CMJ (125DJ > 75DJ > CMJ). There was a significant positive correlation (r = 0.68) between ME and negative work performed across 125DJ, 75DJ and CMJ. These findings suggest that stretch-shortening cycle movements, which include a strenuous braking phase combined with simultaneous high muscle activity, increase ME. This may be due to optimal muscle-tendon unit kinetics and usage of stored elastic energy.     

Analysis of knee movements on leg extension machine: an electromyography study of the rectus femoris muscle

The Rectus Femoris muscle was analyzed by electromyography in 10 female subjects between 19 and 22 years old. Surface electrodes were utilized by placing them at the middle of the muscle. The course of the flexing/extending movements of the knee were analyzed on a Leg Extension Machine. The results showed that the MIC value was greater in the series with loads than in the series without loads. For the Maximum Isometric Contraction (MIC) the value was 144.00. In the movement executed without load the value was 73.96. In the first series with the initial 15 Kg load the value was 163.7 and in the last series of the initial load the value was 194.9. With the 19 Kg load in the first series the value was 182.5 and in the last series the value was 205.1. In the first series with the 21 Kg load the value was 165.1 and in the last series with the 21 Kg load the value was 23.09. The values reflecting the need to recruit more muscle fibers to continue executing the movement. The value 23.09 shows the difficulty in proceeding with the movements and can be considered the beginning of a muscular fatigue process in the Rectus Femoris muscle.     

Reference values of vertical jumping performances in healthy Tunisian adolescent

Background: The assessment of normal values of muscle strength can be determined for the health outcome of adolescents, especially those who are living in a developing country.

Aims: The purpose of this study is to identify the relationship between anthropometric variables and vertical jumping performances. The jump height and the average of power were measured to establish reference values of vertical jumping parameters in Tunisian healthy adolescents aged 13–19 in both sexes.

Subjects and methods: Five hundred and twenty-five school adolescents (242 males and 283 females) were randomly selected to participate in this study. Maximum height and average of power reached in countermovement jump and squat jump were provided by an Optojump device. Full and stepwise regression models were used to identify which anthropometric parameters significantly contributed to performance variables.

Results: All anthropometric parameters increased with age. Reference values and multiple prediction equations of vertical jump parameters were set based on a large sample of healthy Tunisian adolescents. The multiple regressions showed that age, mass, sitting height, waist size, fat-free mass and leg muscle volume for boys and mass for girls were the best predictors of jumping performances.

Conclusion: This study provides normative data for jumping performances in Tunisian healthy adolescents aged 13–19 in both sexes. The percentiles values are calculated to estimate the levels of adolescents with high or low jumping performances.     

Venous blood lactate increase after vertical jumping in volleyball athletes

The aim of this study was to test the hypothesis that venous blood lactate concentrations ([La^–]) would vary from the beginning of brief exercise. Maximal vertical jumping was used as a model of brief intense exercise. Eleven healthy male volleyball players, aged [mean (SE)] 18.5 (0.7) years, performed three exercise tests with different protocols, each separated by quiet seated recovery periods of 45 min. After the first test, consisting of a single maximal jump [lasting ≅0.6 s for the pushing phase, and in which the subjects jumped 64 (2.2) cm], forearm venous [La^–] increased significantly with respect to rest at 1 min (t ₁), 3 min (t ₃), and 5 min (t ₅) of recovery. The second test, comprising six maximal jumps, each separated by 20-s recovery periods, resulted in an unchanged [La^–] with respect to the baseline value. After the third test [i.e., six consecutive maximal jumps that lasted a total of 7.36 (0.33) s], [La^–] increased significantly at t ₃ and t ₅ with respect to the pre-test value (F=10.3, P<0.001). We conclude that a significant venous [La^–] increase occurs after vertical jumping. This result may be explained by the activation of lactic anaerobic metabolism at the very onset of exercise, which participates in energy production and/or in the resynthesis of the phosphocreatine that was used during such brief exercise. Electronic Publication     

Differential effects of countermovement magnitude and volitional effort on vertical jumping

The importance of vertical jumping in sport and rehabilitative medicine is widely recognized. Despite the ample use of jump tests to assess neuromuscular function, the differential effects of muscular activation (volitional effort) and strategy (countermovement magnitude) on jumping performance have not been studied. The present study aimed to investigate the differential effects of countermovement magnitude and volitional effort on vertical jump performance. Ten male participants performed a total of 60 countermovement jumps each with three different countermovement knee angles (50, 70 and 90°) and four effort levels (25, 50, 75 and 100% of maximal effort). Kinematics and Kinetics were recorded using Vicon System together with a force platform. Electromyography of four muscles was recorded. Results show that countermovement magnitude and volitional effort both affect jump performance. These effects were synergistic for jump height (P < 0.001), but antagonistic for peak ground reaction force (P < 0.001). Interestingly, peak jump mechanical power was affected by volitional effort, implying an increase from 31.26 W/kg at 25% to 41.68 W/kg at 100% of volitional effort, but no countermovement magnitude effect was observed for 100% of volitional effort. This suggests that the apparent paradox of larger ground reaction forces in sub-maximal as compared to maximal jumps is due to the different jump strategies. Moreover, these results are relevant for jumping mechanography as a clinical tool, suggesting that peak power can be used to assess neuromuscular performance even when countermovement magnitude varies as a result of age or pathology.     

Neuromuscular function and mechanical efficiency of human leg extensor muscles during jumping exercises

The influence of prestretch amplitude on the mechanical efficiency was examined with 5 subjects, who performed 5 different series of vertical jumps, each of which differed with respect to the mechanics of the knee joint action during the prestretch (eccentric) phase of the contact on the floor. Electromyographic activity was recorded from the major extensor muscles during the entire work period of 1 min per series. In addition, expired air was collected during the test and recovery for determination of energy expenditure. Mechanical work was calculated from the vertical displacement of the body during the jumps. The results indicated that high net efficiency of 38.7% was observed in condition where amplitude of knee bending in eccentric phase was small. In large range motion the corresponding net efficiency was 30.1%. In jumps where no prestretching of extensor muscles ocurred the net efficiency was 19.7%. The high efficiency of small amplitude jumps was characterized by low myoelectrical activity of the leg extensor muscles during the positive (concentric) work phase. In addition, the small amplitude jumps had shorter transition time in the stretch-shortening cycle, high average eccentric force and high stretching speed. Therefore the results suggest that the restitution of elastic energy, which was also related to the length change and stiffness of the muscles during stretch, plays an important role in regulating the mechanical efficiency of work.     

Occipitofrontalis muscle: functional analysis revealed by electromyography

The occipital and frontal bellies of the right occipitofrontalis muscle were studied electromyographically in thirty volunteers in various movements, using a special steel electrode (80 microns diameter). The occipital and frontal bellies have independent actions despite the galea aponeurotica. The frontal belly initially raises the homolateral eyebrow, followed by a displacement of the galea aponeurotica, drawing the scalp forward; therefore it is active in the formation of the transversal wrinkling in the forehead. The occipital belly eventually can be active during raising of the eyebrown, nevertheless it does not interfere with the action of the frontal belly. The occipital belly alone is responsible for drawing back the galea aponeurotica. The occipital belly is also active during smiling and yawning, and can be active during the movements of the auricula.     

A simple test of muscle coactivation estimation using electromyography

In numerous motor tasks, muscles around a joint act coactively to generate opposite torques. A variety of indexes based on electromyography signals have been presented in the literature to quantify muscle coactivation. However, it is not known how to estimate it reliably using such indexes. The goal of this study was to test the reliability of the estimation of muscle coactivation using electromyography. Isometric coactivation was obtained at various muscle activation levels. For this task, any coactivation measurement/index should present the maximal score (100% of coactivation). Two coactivation indexes were applied. In the first, the antagonistic muscle activity (the lower electromyographic signal between two muscles that generate opposite joint torques) is divided by the mean between the agonistic and antagonistic muscle activations. In the second, the ratio between antagonistic and agonistic muscle activation is calculated. Moreover, we computed these indexes considering different electromyographic amplitude normalization procedures. It was found that the first algorithm, with all signals normalized by their respective maximal voluntary coactivation, generates the index closest to the true value (100%), reaching 92 ± 6%. In contrast, the coactivation index value was 82 ± 12% when the second algorithm was applied and the electromyographic signal was not normalized (P < 0.04). The new finding of the present study is that muscle coactivation is more reliably estimated if the EMG signals are normalized by their respective maximal voluntary contraction obtained during maximal coactivation prior to dividing the antagonistic muscle activity by the mean between the agonistic and antagonistic muscle activations.     

Z-band proteins in the flight muscle and leg muscle of the honeybee

Summary Monoclonal antibodies (mAb's) have been raised against proteins in preparations of Z-discs isolated from honeybee fibrillar flight muscle. These antibodies have identified four Z-disc antigens on immunoblots of honeybee fibrillar proteins. Antibody binds to the 90–100 kD protein,-actinin; mAb P interacts with the protein, projectin, an extremely large polypeptide (>600kD) found in the connecting filaments which link thick filaments to the Z-band in insect asynchronous flight muscle. Two other mAb's recognize previously uncharacterized insect Z-band proteins. Monoclonal antibody Z(400) binds to a pair of proteins with molecular masses near 400 kD and 600 kD. Antibody Z(175) recognizes two components, 158 kD and 175 kD, that are not only immunologically similar but have nearly identical peptide maps. Indirect immunofluorescence microscopy studies show that the proteins recognized by mAb's, Z(175) and Z(400) are located at the Z-band, while the mAb P antigen is found on either side of it.Three of the four antibodies we have obtained recognize leg muscle proteins. Monoclonal antibodies and P comigrate on SDS gels with analogous components from flight muscle. Only the smaller of the two proteins identified in flight muscle by mAb Z(400) is found in leg muscle, however. Furthermore, no Z(175) antigens have been detected in the non-fibrillar tissue by either monoclonal or polyclonal antibodies. Immunofluorescence microscopy studies localize the a and Z(400) antigens at the Z-line in leg muscle fibrils. Surprisingly, however, mAb P binds within the A-bands of synchronous fibres, not between the A- and Z-bands as in asynchronous fibrillar muscle.     

Metabolism in exercising arm vs. leg muscle

Arm and leg metabolism were compared by arterial and venous catheterization and blood flow measurements (by dye dilution techniques) in two groups of subjects performing 30-min continuous arm or leg exercise of increasing intensity corresponding to approximately 30, 50 and 80% of max oxygen uptake for arm or leg exercise. The absolute work-loads were 2.5-3 times higher during leg compared to arm exercise. Heart rates were the same in both types of exercise. r-Values were 0.97-1.07 during arm exercise. Arterial noradrenaline and adrenaline levels became higher during leg compared to arm exercise (P less than 0.05-0.01). Arterial lactate concentration was 50% higher for arm exercise at the two lower intensities (P less than 0.001) and the same at the highest intensity compared to leg exercise. Arm lactate release was three times higher (P less than 0.01) or the same as leg lactate output at corresponding exercise intensities. Arm and leg glucose uptake during exercise were of the same magnitude at the lower intensities. In contrast to the leg substrate exchange, arm lactate output was higher than the simultaneous glucose uptake (P less than 0.05-0.001), indicating a relatively higher rate of glycogen degradation. In conclusion, exercising arm compared to leg muscles working at the same relative intensities utilize more carbohydrate, mainly muscle glycogen resulting in higher lactate release by the exercising extremity. This cannot solely be explained on the basis of differences in the degree of training and occurs with lower catecholamine levels compared to leg exercise.     

Mechanics of human triceps surae muscle in walking, running and jumping

Length changes of the muscle-tendon complex (MTC) during activity are in part the result of length changes of the active muscle fibres, the contractile component (CC), and also in part the result of stretch of elastic structures [series-elastic component (SEC)]. We used a force platform and kinematic measurements to determine force and length of the human calf muscle during walking, running and squat jumping. The force-length relation of the SEC was determined in dynamometer experiments on the same four subjects. Length of the CC was calculated as total muscle-tendon length minus the force dependent length of the SEC. The measured relations between force and length or velocity were compared with the individually determined force-length and force-velocity relations of the CC. In walking or running the negative work performed in the eccentric phase was completely stored as elastic energy. This elastic energy was released in the concentric phase, at speeds well exceeding the maximum shortening speed predicted by the Hill force-velocity relation. Speed of the CC, in contrast, was positive and low, well within the range predicted by the measured force-velocity properties and compatible with a favourable muscular efficiency. These effects were also present in purely concentric contractions, like the squatted jump. Contractile component length usually started at the far end of the force-length relation. Inter-individual differences in series-elastic stiffness were reflected in the force and length recordings during natural activity.     

Effect of the leg muscle pump on the rise in muscle perfusion during muscle work in humans

The transient and steady-state effects of the calf muscle pump on the rise in muscle perfusion during rhythmic plantarflexions were investigated in 20 volunteers. Because a large hydrostatic column would increase the effect of a muscle pump, exercise in the supine and head-up tilted positions was compared. Within ~15 s of the start of muscle work, femoral artery flow (ultrasound Doppler) rose 0.37 L/min above rest in the supine and 0.5 L/min above rest in the tilted position. The latter is a significantly larger rise (P < 0.05). After 80 s of muscle work, femoral flow was stable at 0.38 and 0.39 L/min above rest in the supine and tilted positions, respectively. We conclude that the muscle pump contributes to muscle perfusion during the initial phase of muscle work, but that metabolic vasodilation is a more important determinant of muscle perfusion during steady-state muscle work.     

Development of an enhanced leg muscle rehabilitation system

This paper aims to develop an enhanced rehabilitation and assessment system for people with impaired leg muscles, and for people who need to improve their leg muscle function. Through interactive design and real time evaluation, medical staff can totally control the training situation for patients and therefore provide a better training program, so that overall a better treatment performance can be achieved. The system consists of four major parts. Sensory and signal conversion circuits convert the lever arm lengths and muscle strengths of the leg into a proper electronic signal and then deliver this to the computer. Then, the intelligent and interactive interface design lets a trainee complete the training process independently without the involvement of medical staff. In addition, the trainee can see the training results at the end of the training process on the computer screen. The training protection and evaluation mechanism effectively monitors the training situation, based on the individual status settings by the medical staff, and thus any further impairment can be avoided. The database management system is developed to store related personal data, system settings and training results, which can then be retrieved for control and assessment. In comparison to similar equipment the proposed system demonstrates a much better performance, particularly in system functions, accuracy, operation and costs.     

Influence of leg muscle vibration on human walking

We studied the effect of vibratory stimulation of different leg muscles [bilateral quadriceps (Q), hamstring (HS) muscles, triceps surae (TS), and tibialis anterior (TA)] in seven normal subjects during 1) quiet standing, 2) stepping in place movements, and 3) walking on the treadmill. The experiments were performed in a dimly illuminated room, and the subjects were given the instruction not to resist the applied perturbation. In one condition the velocity of the treadmill was controlled by a feedback from the subject's current position. In normal standing, TA vibration elicited a prominent forward body tilt, whereas HS and TS vibration elicited backward trunk or whole body inclination, respectively. Q vibration had little effect. During stepping in place, continuous HS vibration produced an involuntary forward stepping at about 0.3 m s(-1) without modifying the stepping frequency. When the subjects (with eyes closed) kept a hand contact with an external still object, they did not move forward but perceived an illusory forward leg flexion relative to the trunk. Q, TS, and TA vibration did not cause any systematic body translation nor illusory changes in body configuration. In treadmill locomotion, HS vibration produced an involuntary steplike increase of walking speed (by 0.1-0.6 m.s(-1)). Continuous vibration elicited larger speed increments than phasic stimulation during swing or stance phase. For phasic stimulation, HS vibration tended to be more effective when applied during swing than during stance phase. Q, TA, and TS vibration had little if any effect. Vibration of thigh muscles altered the walking speed depending on the direction of progression. During backward locomotion, the walking speed tended to decrease after HS vibration, whereas it significantly increased after Q vibration. Thus the influence of leg muscle vibration on stepping in place and locomotion differed significantly from that on normal posture. We suggest that the proprioceptive input from thigh muscles may convey information about the velocity of the foot movement relative to the trunk.     

Ag/AgCl electrode assembly for thin smooth muscle electromyography

An electrode assembly for in vivo recording of the electrical activities of thin muscular layers is described. It comprises an active electrode surrounded by a ring, which avoids the recording of interfering signals. An improved technique for chlorinating the silver electrodes is presented: a partial electrolytic removal of an initial thick deposit is performed. This decreases the impedance, and lowers the ageing degradation of the electrodes in vivo. Recordings of extremely low frequency signals are allowed, whereas standard Ag/AgCl electrodes are inefficient when recording signals in the frequency domain under 0·1 Hz. The technical features which are described can be adapted to any Ag/AgCl electrode developed for in vivo measurements.     

In vivo determination of muscle viscoelasticity in the human leg

The purpose of this study was to examine the methodological validity of the free vibration technique for determining individual viscoelastic characteristics of the human triceps surae muscle-tendon complex (MTC) in vivo. Six subjects sat with first phalangeal joint of the forefoot on the edge of a force-plate. The special frame on the knee was loaded with weight (0-40 kg) for testing. Oscillations of the triceps surae MTC system were initiated with a hand-held hammer by tapping the weight. In order to keep the same posture, the output of the force plate was displayed on the oscilloscope and subjects were asked to maintain the beam on the oscilloscope at a particular location in relation to a reference line. The damped oscillations in conjunction with the equation of motion of a damped mass-spring model were used to calculate the viscosity of muscle (b) and the elasticity of muscle fibres and tendon (k) in each subject, considering moment arm of the ankle joint. With this arrangement, we have obtained high reproducibility in this method. The coefficient of variations (CVs) of b and k in five trials at each weight were quite small (range: 0.5-18.7% in b and 1.0-15.1% in k). There were no significant differences in viscoelastic coefficients between right and left legs. Therefore, it appears that free vibration technique, used here, is adequate in describing the viscoelastic characteristics of the triceps surae in vivo in humans.