Biomedical subjects

E B Simonsen

Publications and source records attributed to E B Simonsen.

At least 37 records · Page 2Linked to original sources

PubMed1998

Differences in sacral angulation and lumbosacral curvature in black and white young men and women.

The angle between the base of the sacrum and its pelvic surface (SA), and the lumbosacral curve (LSC) defined as the anteroposterior distance between the L1 vertebra and the sacrum were studied in 105 fresh cadavers aged 15-32 years at death. The sample is comprised of 27 black males, 20 black females, 37 white males and 21 white females. Measurements of the SA were made with an adjustable protractor with an accuracy of +/-1 degrees. A new method using a specially designed instrument was developed for taking LSC measurements. A sliding scale that could be moved in the cranialcaudal direction was fitted with a measurement stick which measured the depth of the lumbar and sacral vertebral bodies (ventral to dorsal). The measuring device was placed on the autopsy table above the supine cadaver to measure these depths from the ventral side. The LSC was calculated as the mean difference between lumbar and sacral depths. The SA is smaller in black than in white men (43.6 +/- 3.4 vs. 61.7 +/- 2.1 degrees, p <0.001). Similarly, black women have a smaller SA than white women (36.0 +/- 2.2 vs. 50. 2 +/- 1.9 degrees, p <0.001). The LSC is also larger in black than white men (9.4 +/- 1.1 vs. 5.1 +/- 0.3 cm, p <0.001), and black women also have significantly larger LSC compared to white women (13. 2 +/- 0.5 vs. 9.2 +/- 0.6 cm, p <0.001). These data are so far the largest empirical evidence of differences in the SA and the LSC in young black and white cadaver specimens.

Adolescent↗

PubMed1998

Differences in the iliolumbar ligament and the transverse process of the L5 vertebra in young white and black people.

The anatomy of the iliolumbar ligament (ILL) and the spatial orientation of the transverse process of the L5 vertebra were studied in 62 young black (n = 29) and white (n = 33) men and women during routine autopsy. The aim of the study was to determine possible racial differences in the structure and attachments of the iliolumbar ligament. The present study also investigated the spatial orientation of the transverse process of the L5 vertebra since the ILL has been reported to attach to the transverse process. The measurements of the iliolumbar ligament were carried out with a digital vernier caliper while the transverse process angles were measured with an adjustable protractor. The ligament in black people was made up of a single, markedly longer band compared to white people, where the ligament was made up of two shorter bands. The ILL measured 61.8 +/- 1.3 mm in black and 33.2 +/- 1.5 mm white men, and in black women 61.3 +/- 0.9 mm versus 32.2 +/- 1.2 mm in white women (p <0.01). Further, the ILL was markedly wider in black than white subjects (p <0.01). The horizontal and vertical angle also varied greatly between black and white subjects (p <0.01). These are previously unrecognized observations. Albeit unsubstantiated, these findings may have implications for understanding the etiology of various low back stress problems.

Adolescent↗

PubMed1997

Isokinetic muscle strength and capacity for muscular knee joint stabilization in elite sailors.

In the present study isokinetic dynamometry was used to evaluate the capacity for dynamic knee joint stabilization via muscle contraction in elite sailors (15 males, SM; 6 females, SF) compared to a group of matched controls (8 males, CM). Maximal concentric, eccentric and isometric moment of force (peak moment and moment at 50 degree knee flexion) was obtained for the knee extensors (quadriceps) and flexors (hamstrings) during isokinetic knee joint movement at angular velocities 0, 30, 120 and 180 degrees x s(-1). High levels of eccentric knee extension strength were observed for the elite sailors compared to the controls (p < 0.05). Based on peak moment and 50 degree moment, respectively, conventional hamstring/quadriceps (H/Q) strength ratio (+/-SD) ranged from 0.37+/-0.06 to 0.54+/-0.06 and from 0.42+/-0.07 to 0.57+/-0.10 across groups, speed and contraction mode. The female elite sailors displayed lower (p<0.05) concentric H/Q ratios at 120 and 180 degrees x s(-1) compared to the controls (0.41-0.45 vs. 0.51-0.56, respectively). The ratio of eccentric hamstring to concentric quadriceps strength (H/Q for extension) or concentric hamstring to eccentric quadriceps strength (H/Q for flexion) may provide a more functional estimate of the capacity for muscular knee joint stabilization (1). Based on peak moment and 50 degree moment, respectively, this "functional" H/Q ratio ranged from 0.24+/-0.03 and 0.25+/-0.02 for knee flexion at 180 degrees x s(-1) to 0.97+/-0.17 and 0.88+/-0.12 for knee extension at 180 degrees x s(-1) among the three groups. Comparable levels of "functional" H/Q ratio were observed (p>0.05) for fast knee extension in the elite sailors (SF:0.81-0.97, SM: 0.88-0.95) and the male controls (CM: 0.80-0.84). In conclusion, a "functional" H/Q ratio of 0.8-1.0 observed for all subjects indicated a significant functional capacity of the hamstring muscles for providing muscular stability at the knee joint in fast knee extension. A significant potential for muscular knee joint stabilization appeared for the elite sailors despite their high maximal quadriceps strength and partially lower (SF) conventional H/Q ratios.

Analysis of Variance↗

PubMed1997

Mechanisms contributing to different joint moments observed during human walking.

The present study investigated factors that contribute to the formation of a previously reported knee joint flexor moment during the stance phase of walking. Contradictory results have been reported on this flexor moment, which some but not all individuals exhibit. Seven healthy male subjects were high speed filmed while walking across a force platform, and EMG recordings were obtained from five leg muscles. To investigate segment interactions, net joint moments about the ankle, knee and hip joint were calculated by inverse dynamics and each term in the equation used for the moment calculation was evaluated during the time-course of the step cycle. To test the hypothesis that net joint moments are balanced by an external moment formed by the resulting ground reaction vector multiplied by the perpendicular distance to the actual joint, external moment arms were calculated by the floor reaction force vector approach (FRFV). Contrasting two subjects with different net joint moments about the knee and ankle joint revealed that the knee joint flexor moment could not be explained by an opposite external moment. The external moments were calculated by a simplified method (FRFV) in which the point of force application is incorrect for joints above the ankle joint. However, at the ankle joint the net joint moment was always opposed by an external moment of opposite polarity. A detailed examination of the equation used for the net joint moment calculation showed that a knee joint flexor moment can be caused directly by a large plantar flexor moment about the ankle joint. For example. the soleus muscle can pull the tibia and generate an extensor moment about the knee joint, which in turn has to be opposed by a knee flexor moment from the hamstring muscles. Otherwise the desired joint angles cannot be obtained during human walking. It is therefore suggested that the kinematics regarding how the foot is placed on the ground may influence the net ankle joint moment, while the moment patterns about the knee and hip joint are determined by segment interaction and the requirements for controlling the direction of the resulting ground reaction vector. In vertical jumping it is advantageous to generate extensor moments about the knee and hip joint simultaneously, while in horizontal locomotion this would result in inefficient vertical movements.

Adult↗

PubMed1997

Determinants of musculoskeletal flexibility: viscoelastic properties, cross-sectional area, EMG and stretch tolerance.

Cross-sectional area, stiffness, viscoelastic stress relaxation, stretch tolerance and EMG activity of the human hamstring muscle group were examined in endurance-trained athletes with varying flexibility. Subjects were defined as tight (n = 10) or normal (n = 8) based on a clinical toe-touch test. Cross-sectional area was computed from magnetic resonance imagining (MRI) images. Torque (Nm) offered by the hamstring muscle group, electromyographic (EMG) activity, knee joint angle and velocity were continuously monitored during two standardized stretch protocols. Protocol 1 consisted of a slow stretch at 0.087 rad/s (dynamic phase) to a pre-determined final angle followed by a 90-s static phase. In the dynamic phase final angle and stiffness was lower in tight (28.0+/-2.9 Nm/rad) than normal subjects (54.9+/-6.5 Nm/rad), P<0.01. In the static phase tight subjects had lower peak (15.4+/-1.8 Nm) and final torque (10.8+/-1.6 Nm) than normal subjects (31.6+/-4.1 Nm, 24.1+/-3.7 Nm, respectively)(P<0.01), but torque decline was similar. Protocol 2 consisted of a slow stretch to the point of pain and here tight subjects reached a lower maximal angle, torque, stiffness and energy than normal subjects (P<0.01). On the other hand, stiffness was greater in tight subjects in the common range (P<0.01). Cross-sectional area of the hamstring muscles and EMG activity during the stretch did not differ between the groups. However, lateral hamstring cross-sectional area was positively related to mid-range stiffness (P<0.05), but inversely related to final stiffness, peak torque and the toe-touch test (P<0.01). Final angle and peak torque in protocol 1 combined to improve the predictability of the toe-touch test (R2=0.77, P<0.001). These data show that the toe-touch test is largely a measure of hamstring flexibility. Further, subjects with a restricted joint range of movement on a clinical toe-touch test have stiffer hamstring muscles and a lower stretch tolerance.

Biomechanical Phenomena↗

PubMed1996

A mechanism for altered flexibility in human skeletal muscle.

1. We investigated the effect of a long-term stretching regimen on the tissue properties and stretch tolerance of human skeletal muscle. 2. Resistance to stretch was measured as torque (in N m) offered by the hamstring muscle group during passive knee extension while electromyographic (EMG) activity, knee joint angle and velocity were continuously monitored during a standardized stretch manoeuvre. Seven healthy subjects were tested before and after a 3 week training period using two separate protocols. Protocol 1 consisted of a slow stretch at 0.087 rad s-1 to a predetermined angle followed by a 90 s holding phase. Subjects were brought to the same angle before and after the training period. Protocol 2 was a similar stretch, but continued to the point of pain. 3. During protocol 1 the torque rose during the stretch and then declined during the holding phase. EMG activity was small and did not change significantly during the protocol. No significant differences in stiffness, energy and peak torque about the knee joint were seen as a result of the training. During protocol 2 the angle to which the knee could be extended was significantly increased as a result of the training. This was accompanied by a comparable increase in peak torque and energy. EMG activity was small and not affected by training. 4. It is concluded that reflex EMG activity does not limit the range of movement during slow stretches and that the increased range of motion achieved from training is a consequence of increased stretch tolerance on the part of the subject rather than a change in the mechanical or viscoelastic properties of the muscle.

Adult↗

PubMed1996

Mechanical and physical responses to stretching with and without preisometric contraction in human skeletal muscle.

OBJECTIVE: To examine electromyography (EMG) activity, passive torque, and stretch perception during static stretch and contract-relax stretch. DESIGN: Two separate randomized crossover protocols: (1) a constant angle protocol on the right side, and (2) a variable angle protocol on the left side. SUBJECTS: 10 male volunteers. INTERVENTION: Stretch-induced mechanical response in the hamstring muscles during passive knee extension was measured as knee flexion torque (Nm) while hamstring surface EMG was measured. Final position was determined by extending the knee to an angle that provoked a sensation similar to a stretch maneuver. Constant angle stretch: The knee was extended to 10 degree below final position, held 10sec, then extended to the final position and held for 80 sec. Variable angle stretch: The knee was extended from the starting position to 10 degrees below the final position, held 10sec, then extended to the onset of pain. Subjects produced a 6-sec isometric contraction with the hamstring muscles 10 degrees below the final position in the contract-relax stretch, but not in the static stretch. MAIN OUTCOME MEASURES: Passive torque, joint range of motion, velocity, and hamstring EMG were continuously recorded. RESULTS: Constant angle contract-relax and static stretch did not differ in passive torque or EMG response. In the final position, passive torque declined 18% to 21% in both contract-relax and static stretch (p<.001), while EMG activity was unchanged. In the variable angle protocol, maximal joint angle and corresponding passive torque were significantly greater in contract-relax compared with static stretch(p<.01), while EMG did not differ. CONCLUSION: At a constant angle the viscoelastic and EMG response was unaffected by the isometric contraction. The variable angle protocol demonstrated that PNF stretching altered stretch perception.

Adult↗

PubMed1996

Specificity of training velocity and training load on gains in isokinetic knee joint strength.

The present study investigated the effects of three different strength training regimes on the isokinetic strength profile of the knee extensors (quadriceps, Q) and flexors (hamstrings, H) and if increases in isokinetic strength were accompanied by an enhanced performance during a more complex leg movement, the soccer kick. Twenty-two elite soccer players performed 12 weeks of strength training (three times per week) at either high resistance (HR group: 4 sets, 8 reps, 8RM loading), low resistance (LR group: 4 sets, 24 reps, 24RM loading), loaded kicking movements (LK group: 4 sets, 16 reps, 16RM loading) while one group served as controls (CO group). Isokinetic concentric and eccentric moment of force was obtained (KinCom) as peak moment (Mpeak) and moment at 50 degrees knee flexion (M50) at angular velocities of 30, 120, 240 degrees s-1. Isokinetic knee joint strength was unchanged in groups LR, LK, CO. However, after the HR strength training, concentric Mpeak (+/- SD) increased (P < 0.01) at 30 degrees s-1 (Q, 258 +/- 37 to 297 +/- 57 Nm; H, 122 +/- 22 to 140 +/- 21 Nm). Furthermore, eccentric Mpeak increased at 30, 120 and 240 degrees s-1 (Q, 274 +/- 60 to 345 +/- 57 Nm (P < 0.01), 291 +/- 56 to 309 +/- 49 Nm and 275 +/- 43 to 293 +/- 36 Nm (P < 0.05), respectively; H, 143 +/- 32 to 158 +/- 25 Nm, 152 +/- 39 to 169 +/- 31 Nm and 148 +/- 27 to 163 +/- 19 Nm (P < 0.05)). Corresponding increases (P < 0.05) were observed for M50. The H/Q ratio calculated as eccentric hamstring strength divided by concentric quadriceps strength (Hecc/Qcon, representative for knee extension) at 240 degrees s-1 increased (P < 0.05) from 107 to 118% (based on Mpeak) and from 90 to 105% (M50). Kicking performance estimated by maximal ball flight velocity was unaffected by any of the strength training regimes investigated. In conclusion, only heavy-resistance strength training induced increases in isokinetic muscle strength in the absence of learning effects. Concentric strength gains were observed at the actual velocity of training, while eccentric strength gains were found over the entire range of velocities examined. The capacity of the hamstring muscles for providing stability to the knee joint during fast extension was augmented as a result of the heavy-resistance strength training. Strength training should be integrated with other types of training involving the actual movement pattern in order to increase the performance within more complex movement patterns.

Adult↗

PubMed1996

Dynamics of the martial arts high front kick.

Fast unloaded movements (i.e. striking, throwing and kicking) are typically performed in a proximo-distal sequence, where initially high proximal segments accelerate while distal segments lag behind, after which proximal segments decelerate while distal segments accelerate. The aims of this study were to examine whether proximal segment deceleration is performed actively by antagonist muscles or is a passive consequence of distal segment movement, and whether distal segment acceleration is enhanced by proximal segment deceleration. Seventeen skilled taekwon-do practitioners were filmed using a high-speed camera while performing a high front kick. During kicking, EMG recordings were obtained from five major lower extremity muscles. Based on the kinematic data, inverse dynamics computations were performed yielding muscle moments and motion-dependent moments. The results indicated that thigh deceleration was caused by motion-dependent moments arising from lower leg motion and not by active deceleration. This was supported by the EMG recordings. Lower leg acceleration was caused partly by a knee extensor muscle moment and partly by a motion-dependent moment arising from thigh angular velocity. Thus, lower leg acceleration was not enhanced by thigh deceleration. On the contrary, thigh deceleration, although not desirable, is unavoidable because of lower leg acceleration.

Adolescent↗

PubMed1996

Viscoelastic stress relaxation during static stretch in human skeletal muscle in the absence of EMG activity.

The present study sought to investigate the role of EMG activity during passive static stretch. EMG and passive resistance were measured during static stretching of human skeletal muscle in eight neurologically intact control subjects and six spinal cord-injured (SCI) subjects with complete motor loss. Resistance to stretch offered by the hamstring muscles during passive knee extension was defined as passive torque (Nm). The knee was passively extended at 5 degrees/s to a predetermined final position, where it remained stationary for 90 s (static phase) while force and integrated EMG of the hamstring muscle were recorded. EMG was sampled for frequency domain analysis in a second stretch maneuver in five control and three SCI subjects. There was a decline in passive torque in the 90-s static phase for both control and SCI subjects, P < 0.05. Although peak passive torque was greater in control subjects, P < 0.05, there was no difference in time-dependent passive torque response between control (33%) and SCI (38%) subjects. Initial and final 5-s IEMG ranged from 1.8 to 3.4 microV.s and did not change during a stretch or differ between control and SCI subjects. Frequency domain analysis yielded similar results in both groups, with an equal energy distribution in all harmonics, indicative of 'white noise'. The present data demonstrate that no measurable EMG activity was detected in either group during the static stretch maneuver. Therefore, the decline in resistance to static stretch was a viscoelastic stress relaxation response.

Adolescent↗

PubMed1995

Mechanical and muscular factors influencing the performance in maximal vertical jumping after different prestretch loads.

The objective of the present work was to study the interaction between the tendon elasticity, the muscle activation-loading dynamics, specific actions of the biarticular muscles, preloading and jumping performance during maximal vertical jumping. Six male expert jumpers participated in the study. They performed maximal vertical jumps with five different preloads. The kinematics and dynamics of the jumping movements were analysed from force plate and high speed film recordings. The amount of elastic energy stored in the tendons of the leg extensor muscles was calculated by a generalised tendon model, and the muscle coordination was analysed by surface EMG. The best jumping performances were achieved in the jumps with low preloads (counter movement jumps and drop jumps from 0.3 m). A considerable amount of the energy imposed on the legs by prestretch loading was stored in the tendons (26 +/- 3%), but the increased performance could not be explained by a contribution of elastic energy to the positive work performed during the push off. During the preloading, the involved muscles were activated at the onset of the loading. Slow prestretches at the onset of muscle activation under relatively low average stretch loads, as observed during counter movement jumps and drop jumps from 0.3 m, prevented excessive stretching of the muscle fibres in relation to the tendon length changes. This consequently conserved the potential of the muscle fibres to produce positive work during the following muscle-tendon shortening in concert with the release of the tendon strain energy. A significant increase in the activity of m. rectus femoris between jumps with and without prestretch indicated a pronounced action of m. rectus femoris in a transport of mechanical energy produced by the proximal monoarticular m. gluteus maximus at the hip to the knee and thereby enhanced the transformation of rotational joint work to translational work on the mass centre of the body. The changes in muscle activity were reflected in the net muscle powers. Vertical jumping is like most movements constrained by the intended direction of the movement. The movements of the body segments during the prestretches induced a forward rotation and during the take off, a backward rotation of the body. A reciprocal shift in the activities of the biarticular m. rectus femoris and m. semitendinosus indicated that these rotations were counteracted by changes in the direction of the resultant ground reaction vector controlled by these muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1995

The influence of tendon Youngs modulus, dimensions and instantaneous moment arms on the efficiency of human movement.

The purpose of the study was to examine the influence of passive tendon work on the gross mechanical efficiency of human whole body movement. Seven male subjects participated in the study. They performed repetitive jumps (like skipping) of three different intensities. Metabolic costs and work rates were recorded to obtain mechanical efficiencies. Net joint moments were calculated from film recordings using inverse dynamics. A general stress-strain relationship for tendons was modelled using a quadratic function, including Youngs elastic modulus of tendon tissue and tendon dimensions. Instantaneous tendon moment arms for the largest leg extensor muscles (m. triceps surae and m. quadriceps femoris) were calculated using joint angle-moment arm transfer functions obtained from the literature (cadaver studies) and the tendon work was calculated from the net joint moments. Gross efficiency values of 0.65-0.69 and efficiency values of 0.77-0.80 at the approximate level of the muscle-tendon complexes were observed. The tendons performed 52-60% of the total work. The enhancement of the muscle-tendon efficiency over the maximal theoretical efficiency of the contractile machinery (0.30) could exclusively be explained by the contribution of the tendon work. A clear negative relationship between repetitive jumping with high mechanical efficiency and running economy at 12 km h-1 was found. Using model calculations the gross efficiency and the muscle-tendon efficiency were shown to be sensitive to tendon Youngs modulus, dimensions and moment arms. The efficiencies were most sensitive to changes in the tendon moment arms. A 10% decrease in tendon moment arms resulted in a 13% increase in the gross efficiency. Optimization or minimisation of the mechanical efficiency by changing the tendon variables 5% was followed by changes in mechanical efficiency of +14% and -10%, respectively.

Adult↗

PubMed1995

The influence of strength training, swim training and ageing on the Achilles tendon and m. soleus of the rat.

Different age groups of male Wistar rates were submitted to intense strength training, swim training or no training. It was found that the tetanic of the m. soleus decreased with age. This was counteracted by strength training, whereas swim training had no effect on tetanic tension. Force at ultimate failure and yield point in the Achilles tendon decreased with age, but were not influenced by strength training. Swim training, on the other hand, appeared to compensate for the ageing process in the tendon. We conclude that tendon strength decreases with age and that tendon strength does not reflect muscle strength. The absolute tensile strength of tendons appears to be influenced by physical activity of endurance-type exercise. However, it is not known whether the tissue responds to the number of mechanical muscle contractions or physiological factors connected with endurance training. Although it is questionable to extrapolate from the rat to humans, it is speculated that intensive muscle strength training should be accompanied by endurance exercise in order to prevent the muscles from damaging connective tissue structures, such as the tendons and ligaments.

Achilles Tendon↗

PubMed1995

Viscoelastic response to repeated static stretching in the human hamstring muscle.

The purpose of this study was (1) to evaluate the reproducibility of a new method of measuring passive resistance to stretch in the human hamstring muscle group, in vivo, using a test re-test protocol and 2) to examine the effect of repeated stretches. Passive resistance offered by the hamstring muscle group during knee extension was measured in 10 subjects as knee flexion moment (Nm) using a KinCom dynamometer. The knee was passively extended at 5 deg/s to the final position where it remained stationary for 90 s (static phase). EMG of the hamstring muscle was also measured. The test re-test protocol included 2 tests (tests 1 and 2) administered 1 h apart. On a separate occasion 5 consecutive static stretches were administered (stretches 1-5) separted by 30 s. Stretch 6 was administered one hour after stretch 5. In the static phase passive resistance did not differ between test 1 and test 2. Resistance declined in both tests 1 and 2, whereas EMG activity remained unchanged. The decline in resistance was significant up to 45 s. For the repeated stretches there was an effect of time (90 s) and stretch (1-5) with a significant interaction i.e., resistance diminished with stretches, and the 90-s decline was less as more stretches were performed. Passive resistance in stretch 6 was lower than in stretch 1. The present study has demonstrated a reliable method for studying resistance to stretch of the human hamstring muscle group. A viscoelastic response of the human hamstring muscle was shown. With 5 repeated stretches, resistance to stretch diminished and each stretch exibited a viscoelastic response, albeit less with each subsequent stretch. The effect of 5 repeated stretches was significant 1 h later.

Adult↗

PubMed1995

Excitability of the soleus H reflex during graded walking in humans.

The excitability of the soleus Hoffmann (H) reflex was measured in five healthy male subjects during graded treadmill walking. Uphill and downhill walking at an 8% grade as well as level walking were used to vary the demands for lengthening and shortening contractions of the soleus muscle. These changes were assumed to cause differences in control of the afferent input in the spinal cord and the voluntary output to the soleus muscle. The H reflex was strongly modulated in all three walking conditions, high during the stance phase and low or absent during the swing phase. The shape of the modulations was, however, different. At uphill walking the reflex increased gradually during the whole stance phase and seemed to follow the soleus electromyogram (EMG) pattern closely. In the downhill condition the reflex excitability increased rapidly at heel strike like the soleus EMG and co-contraction of the anterior tibial muscle was observed. At level walking a fast rise in reflex excitability was seen just after heel strike with low or absent soleus EMG. Mean soleus EMG was lower during downhill than during uphill or level walking, but the mean H reflex amplitude was similar in all three conditions. However, when the H reflex was related directly to the EMG activity by linear regression the reflex gain was lower during uphill walking than in the two other conditions. Furthermore, the ratio between H reflex and EMG amplitude was high during the first half of the stance phase at level walking indicating an elevated reflex excitability independent of the voluntary motor output. It is therefore concluded that the modulation of reflexes during walking cannot be interpreted in terms of the idea of automatic gain compensation. The reflexes must be controlled specifically and independently during the different phases of the motor output to meet the mechanical requirements of the movement task. Most explicitly this was seen during downhill walking, where an elevated reflex excitability together with co-contraction at the ankle joint seem to provide increased joint stiffness and security, when the kinetic energy of the body has to be brought under control at heel strike.

Adult↗

PubMed1995

Isokinetic hamstring/quadriceps strength ratio: influence from joint angular velocity, gravity correction and contraction mode.

This study investigated isokinetic peak- and angle-specific hamstring/quadriceps strength ratios (conventional H/Q ratio) obtained during concentric and eccentric muscle contraction and examined the influence of joint angular velocity and the effect of gravity correction on these ratios. Also, a 'functional' H/Q ratio was defined by calculating eccentric hamstring strength relative to concentric quadriceps strength (Hecc/Qcon' representative for knee extension) and calculating concentric hamstring strength relative to eccentric quadriceps strength (Hcon/Qecc' representative for knee flexion). The H/Q ratio was calculated based on isokinetic peak moment and 50 degree-moment (0 degree = full extension) obtained at joint angular velocities 30, 120 and 240 degrees s-1. Gravity corrected conventional H/Q ratio remained constant across speeds and contraction mode, ranging from 0.47 to 0.54 and from 0.49 to 0.56 based on peak and 50 degree moment, respectively. In contrast, non-corrected H/Q ratio increased during concentric contraction from 0.58 at 30 degrees s-1 to 0.74 at 240 degree s-1 (P < 0.01). For knee extension at 240 degrees s-1 an Hecc/Qcon of 1.05 (peak) and 0.89 (50 degrees) was observed while for flexion at 240 degrees s-1 an Hcon/Qecc of 0.27 (peak) and 0.28 (50 degrees) was observed. In conclusion, gravity correction had high influence on the change in H/Q ratio with variation in extension velocity. A potential 1:1 hamstring/quadriceps strength relationship was demonstrated for fast knee extension, indicating a significant functional capacity of the hamstring muscles for providing muscular stability at the knee joint in such situations.

Adult↗

PubMed1995

Contraction specific changes in passive torque in human skeletal muscle.

The present investigation examined passive torque and electromyographic response in human skeletal muscle during passive static stretch within 60 s after maximal repetitive eccentric and concentric contractions. Passive torque (Nm) offered by the hamstring muscle group was measured during passive knee extension in a modified dynamometer in 10 subjects. The distal thigh was elevated to 0.52 rad from horizontal and the backrest was positioned at 1.57 rad. The lever arm moved the leg passively at 0.09 rad s-1 from a starting position of 1.48 rad below horizontal to the final position where it remained stationary for 90 s. Gross electrical activity of the human hamstring muscle group was recorded simultaneously. The effect of concentric or eccentric contraction was tested on separate days. Two stretch manoeuvres with a 45 min hiatus were administered on a control and experimental side. The experimental side performed 40 maximal effort repetitive concentric or eccentric hamstring muscle contractions at 1.05 rad s-1 prior to the second stretch. Passive torque during the 90 s stretch declined 30-35% on the experimental and control side in all stretches, P < 0.001, without a significant effect of prior contraction mode. Passive peak and final torques were lower on the experimental side, P < 0.01 after concentric contractions. Passive peak and final torques remained unchanged after eccentric contractions on the experimental side. The low level EMG response of the hamstring muscle during the stretch was unchanged after maximal repetitive concentric or eccentric contractions. These data demonstrate acute contraction specific alteration in passive torque in human skeletal muscle, which cannot be accounted for by EMG activity. Furthermore, the lack of difference on the control side implies that one 90 s stretch has no effect on passive torque of the muscle 45 min later.

Adult↗

PubMed1995

Bone-on-bone forces during loaded and unloaded walking.

Joint moments and bone-on-bone forces in the ankle, knee and hip joint were studied in 7 healthy male subjects during unloaded and loaded walking. The subjects walked across a force platform while they were filmed at 200 Hz. Loaded walking was examined at 10 and 20 kg load carried symmetrically in the hands. Peak joint moments and peak bone-on-bone forces increased from unloaded to loaded walking for the ankle and hip joint (p < 0.05). The lowest bone-on-bone forces were found at the ankle joint (3,318 +/- 390 N) during unloaded walking and the highest at the hip joint (6,399 +/- 1,517 N) during 20 kg loading. Expressed relative to body weight (BW) these values corresponded to 4.2 +/- 0.50 and 8.0 +/- 1.78 BW). However, the individual values showed that 2 of the 7 subjects differed remarkably from the other 5, especially with respect to the hip joint loadings. During loaded walking (20 kg) these 2 subjects showed 14.4 and 15.1 BW peak compression force in the hip joint while the remaining subjects were all below 6.3 BW, which could be explained by the 2 subjects' low ankle joint moments and higher knee and hip joint moments. Apparently, a total 'leg moment' formed by the three major joints is required to support the body and maintain the locomotion, although the relative contribution from each joint can differ among individuals. The peak joint moments were the most dominant contributor to the peak bone-on-bone forces. Therefore, it is concluded that interindividual differences in walking style can lead to pronounced differences in peak bone-on-bone forces. It remains unclear how these interindividual differences are related to joint degradation.

Adult↗