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PubMed1996

Isokinetic performance capacity of trunk muscles. Part I: The effect of repetition on measurement of isokinetic performance capacity of trunk muscles among healthy controls and two different groups of low-back pain patients.

The aim of this investigation was to assess the reproducibility of the isokinetic trunk muscle performance measurement among patients with different degrees of low-back pain. Twenty-two healthy volunteers, 20 patients with mild and 18 patients with severe low-back pain participated in isokinetic measurements. Lidoback isokinetic dynamometer was used. The measurements were performed with the subjects standing, using velocities of 60, 90 and 120 degrees/second. Five repetitions were performed at each velocity. All subjects were tested three times with a 1-week interval between the tests. Peak torque, average peak torque, coefficient of variation, total work done and peak torque to body weight ratio were calculated for each velocity for both flexion and extension. The results showed that in every measurement peak torque, average peak torque, peak torque to body weight ratio and total work done correlated with each other very strongly both in flexion and extension (r > or = 0.9). The average peak torques increased in further measurements. The change had a strong correlation with the severity of the back problem, which was evaluated by means of the Oswestry disability index. The critical value was found to be 20% in the Oswestry index: values above this meant big changes between measurements and values below this meant small changes between measurements.

Adult↗
PubMed2006

Strength deficits in primary focal hand dystonia.

Cortical activation is reduced when patients with focal dystonia perform movements that do not induce dystonic posturing. This finding suggests that the cortical drive to muscles may in some circumstances actually be reduced not increased, as suggested by basal ganglia models of dystonia as a hyperkinetic disorder. The purpose of this study was to examine flexor and extensor strength at the wrist (a clinically affected joint) and elbow (a nonclinically affected joint) in 18 patients with primary focal hand dystonia compared to matched control subjects. We measured peak torque from maximum voluntary contractions, and agonist and antagonist muscle activation by means of surface electromyograms. Patients were significantly weaker than controls at both the elbow and wrist joints and in both flexors and extensors compared to controls. Peak elbow flexion torque was, on average, 14.4% lower in the dystonic compared to the control group, elbow extensor peak torque was 28.6% lower, wrist flexor peak torque was 17.4% lower, and wrist extensor peak torque was 20.7% lower. Strength did not differ as a function of clinical severity. Reductions in peak torque were accompanied by reduced agonist activation, although this finding only reached statistical significance at the elbow. The amount of co-contraction of antagonistic muscles was not significantly different between the two groups. These results are discussed in the context of dystonia as a disorder resulting from dysfunction of basal ganglia output.

Adult↗
PubMed2004

Assessment of voluntary activation by stimulation of one muscle or two synergistic muscles.

In order to test the hypothesis that suboptimal activation of synergistic muscles explains the nonlinear nature of the interpolated twitch-voluntary torque relationship, we evaluated differences between stimulating a single muscle [biceps brachii (BB)] and two synergists simultaneously [BB and brachioradialis (BR)] on variables related to the estimation of voluntary activation. Ten subjects performed maximal and submaximal voluntary contractions while electrical stimulation was applied either to the BB, or BB and BR simultaneously, to assess voluntary activation. Simultaneous stimulation of the two synergistic muscles produced significantly greater torque at rest and a significantly greater activation index (95% vs. 91.7% for stimulation of BB only). However, simultaneous stimulation of BB and BR did not consistently elicit greater additional torque during contraction, nor did it improve the linearity of the interpolated twitch-voluntary torque relationship. The greater activation index observed for the simultaneous stimulation of BB and BR compared to BB is explained by the greater torque elicited at rest. We conclude that the nonlinear relationship between interpolated and voluntary elbow flexion torque is not explained by suboptimally activated synergistic muscles.

Adult↗
PubMed2005

Influence of knee joint angle on muscle properties of paralyzed and nonparalyzed human knee extensors.

Muscles of individuals with a spinal cord injury (SCI) exhibit an unexpected leftward shift in the force (torque)-frequency relationship. We investigated whether differences in torque-angle relationships between SCI and able-bodied control muscles could explain this shift. Electrically stimulated knee-extensor contractions were obtained at knee flexion angles of between 30 degrees and 90 degrees. Torque-frequency relationships were obtained at 30 degrees, 90 degrees, and optimum angle. Optimum angle was not different between groups but SCI-normalized torques were lower at the extreme angles. At all angles, SCI muscles produced higher relative torques at low stimulation frequencies. Thus, there was no evidence of a consistent change in the length of paralyzed SCI muscles, and the anomalous leftward shift in the torque-frequency relationship was not the result of testing the muscle at a relatively long length. The results provide valuable information about muscle changes occurring in various neurological disorders.

Adult↗
PubMed1996

Co-activation and tension-regulating phenomena during isokinetic knee extension in sedentary and highly skilled humans.

The aim of this study was to examine isokinetic torque produced by highly skilled (HS) and sedentary (S) human subjects, during knee extension, during maximal voluntary and superimposed electrical activation. To verify the level of activation of agonist (vastus lateralis, VL, and vastus medialis, VM) and antagonist muscles (semi-tendineous, ST), during maximal voluntary activation, their myo-electrical activities were detected and quantified as root mean square (rms) amplitude. Ten HS and ten S subjects performed voluntary and superimposed isometric actions and isokinetic knee extensions at 14 angular velocities (from -120 to 300 degrees*s(-1)). The rms amplitude of each muscle was normalized with respect to its rms amplitude when acting as agonist at 15 degrees*s(-1). Whatever the angular velocity considered, peak torque and constant angular torque at 65 degrees of HS were significantly higher (P <0.05) than those of S. Eccentric superimposed torque of S, but not HS, was significantly higher (P <0.05) than voluntary torque at -120, -90, - 60 and - 30 degrees*s(-1) angular velocities. For a given velocity, the rms amplitude of VL and VM were significantly lower (P <0.05), during eccentric than during concentric actions, in S, but not in HS. However, whatever the angular velocity, ST co-activation in HS was significantly lower (P < 0.05) than in S. We concluded that co-activation phenomenon could partly explain differences in isokinetic performances. Differences between voluntary and superimposed eccentric torques as well as lower agonist rms amplitude during eccentric action in S, support the possibility of the presence of a tension-regulating mechanism in sedentary subjects.

Adult↗
PubMed2003

Kinematics of wrist joint flexion in overarm throws made by skilled subjects.

Previous studies of multijoint arm movements have shown that the CNS holds arm kinematics constant in different situations by predictively compensating for the effects of interaction torques. We determined whether this was also the case for wrist joint flexion in natural overarm throws performed by skilled subjects in 3D, a situation where large passive torques can occur at the wrist. Specifically, we investigated whether wrist flexion amplitudes are held constant in throws of different speeds. Joint rotations were recorded at 1,000 Hz with the search-coil technique. Contrary to a previous study on constrained 2D throwing, indirect evidence was found that in fast throws passive torques associated with forearm deceleration were exploited to increase wrist flexion velocity. This increase in wrist flexion velocity was associated with constant wrist flexion amplitudes at ball release (mean 27 degrees) for throws of different speeds. Furthermore, final wrist flexion positions after ball release were similar for a particular subject irrespective of the speed of the throw. This was associated in faster throws with increased magnitudes of wrist flexor and wrist extensor EMG activity which damped passive torques associated with forearm angular deceleration. It is concluded that wrist flexion in overarm throws of different speeds is produced by central signals which precisely control net joint torque by both exploiting and damping passive torques during different parts of the throw to keep wrist joint angular position parameters constant. As such the results show that control strategies for natural 3D throwing are different from those for constrained 2D throwing.

Arm↗
PubMed2004

The role of shortening reaction in mediating rigidity in Parkinson's disease.

Rigidity in Parkinson's disease (PD) is defined as an increased resistance to passive movement of a joint. The plastic-type rigidity is uniform and constant throughout the entire range of motion, whereas the cogwheel-type rigidity is accompanied by tremor. Rigidity in PD has been understudied. Thus, its pathophysiological basis remains unclear. The purpose of the study is to examine neuromuscular/biomechanical properties of PD rigidity and to provide its physiological characteristics. We hypothesize that PD rigidity presents as a flattened trace of joint torque vs. angular position (torque-angle relation) of the wrist, because the forces generated by lengthening muscles are offset by activation of the antagonist, i.e. show "shortening reaction" (SR). Experiments were conducted on six PD subjects medication OFF and ON. PD severity was assessed based on the unified Parkinson's disease rating scale. Each subject sat on a chair and was instructed to relax, with the wrist coupled to the device. The servomotor applied constant velocity displacement to create wrist flexion/extension. Electromyographic (EMG) responses were monitored from wrist muscles, along with position, velocity and torque. EMG magnitudes were computed over the movement period. Slopes were derived from the torque-angle trace. Results showed that SRs were routinely recorded OFF medication, but substantially reduced ON medication. Due to the interaction of SR, torque-angle relation was flatter OFF medication and became steeper ON medication. Correlation analyses showed that a strong correlation (R=0.65) existed between SR and torque-angle slope OFF medication, exclusively. We suggest that SR may play an important role in mediating the mechanical features of PD rigidity.

Adult↗
PubMed2006

Effects of friction at the digit-object interface on the digit forces in multi-finger prehension.

The effects of surface friction at the digit-object interface on digit forces were studied when subjects (n=8) statically held an object in a five-digit grasp. The friction conditions were SS (all surfaces are sandpaper), RR (all are rayon), SR (S for the thumb and R for the four fingers), and RS (the reverse of SR). The interaction effects of surface friction and external torque were also examined using five torques (-0.5, -0.25, 0, +0.25, +0.5 Nm). Forces and moments exerted by the digits on a handle were recorded. At zero torque conditions, in the SS and RR (symmetric) tasks the normal forces of the thumb and virtual finger (VF, an imagined finger with the mechanical effect equal to that of the four fingers) were larger for the RR than the SS conditions. In the SR and RS (asymmetric) tasks, the normal forces were between the RR and SS conditions. Tangential forces were smaller at the more slippery side than at the less slippery side. According to the mathematical optimization analysis decreasing the tangential forces at the more slippery sides decreases the cost function values. The difference between the thumb and VF tangential forces, DeltaF (t), generated a moment of the tangential forces (friction-induced moment). At non-zero torque conditions the friction-induced moment and the moment counterbalancing the external torque (equilibrium-necessitated moment) could be in same or in opposite directions. When the two moments were in the same direction, the contribution of the moment of tangential forces to the total moment was large, and the normal forces were relatively low. In contrast, when the two moments were in opposite directions, the contribution of the moment of tangential forces to the total moment markedly decreased, which was compensated by an increase in the moment of normal forces. The apparently complicated results were explained as the result of summation of the friction-related (elemental) and torque-related (synergy) components of the central commands to the individual digits.

Adaptation, Physiological↗
PubMed2004

Mechanical power during maximal treadmill walking and running in young and elderly men.

This study determined mechanical power during movements specific to maximal walking and running using a non-motorized treadmill in 38 elderly [69.4 (5.0) years] and 50 young [24.3 (3.4) years] men. The mean mechanical power over a period of time covering six steps, during which the belt velocity peaked and then kept almost plateau, was determined as a performance score in each of maximal walking (WP) and running (RP). In terms of the value relative to body mass, the relative difference between the two age groups was greater for RP (61.7%) than for WP (21.4%) or isometric knee extension (34.1%) and flexion torque (43.8%). In the two groups, WP was significantly ( P<0.05) correlated to knee extension (r=0.582 for the elderly and r=0.392 for the young) and flexion torque (r=0.524 for the elderly and r=0.574 for the young). Similarly, RP was also significantly (P<0.05) correlated to knee extension (r=0.627 for the elderly and r=0.478 for the young) and flexion torque (r=0.500 for the elderly and r=0.281 for the young). In these relationships, the WP adjusted statistically by thigh muscle torque was similar in the two age groups. However, the corresponding value for RP was significantly higher in the young than in the elderly. The findings here indicate that: (1) the difference between the young and elderly men in mechanical power is greater during maximal running than maximal walking, and (2) although the thigh muscle torque contributes to the power production during the two maximal exercise modes in the two age groups, the RP is greater in the young than in the elderly regardless of the difference in the thigh muscle torque.

Adult↗
PubMed2004

Acute passive stretching alters the mechanical properties of human plantar flexors and the optimal angle for maximal voluntary contraction.

The purpose of this study was to investigate whether acute passive stretching (APS) reduced maximal isometric voluntary contraction (MVC) of the plantar flexors (PF) and if so, by what mechanisms. The PF in 15 female volunteers were stretched for 10 min (5 x 120 s) by a torque motor to within 2 degrees of maximum dorsiflexion (D) range of motion (ROM). MVC with twitch interpolation, maximal Hoffmann reflex (H(max)) and compound action potentials (M(max)) were recorded at 20 degrees D. Stretch reflexes (SR) were mechanically induced at 200 degrees s(-1) between 0 degrees and 10 degrees ( )D and SR torque and EMG amplitude were determined. All tests were assessed pre- (pre) and post-APS (post-test(1)). MVC, SR, and M(max) were again assessed after additional stretch was applied [mean 26 (1) degrees D; post-test(2)] to test if the optimal angle had been altered. EMG was recorded from soleus (SOL), medial gastrocnemius (MG) and tibialis anterior (TA) using bipolar surface electrodes. APS resulted in a 27% decrease in mean peak passive torque (P<0.05). MVC and SR torque were 7% (P<0.05) and 13% lower at post-test(1) (P<0.05), respectively. SR EMG amplitude of SOL and MG was reduced by 27% (P<0.05) and 22% (P<0.05), respectively. The H(max)/M(max) EMG and H(max)/M(max) torque ratios were unchanged at post-test(1). At post-test(2), MVC and SR EMG recovered to pre-APS values, while the SR and M(max) torque increased by 19% and 13%, respectively (P<0.05). The decrease in MVC during post-test(1) was attributed to changes in the mechanical properties of PF and not to reduced muscle activation.

Adult↗
PubMed2001

Adaptation to chronic eccentric exercise in humans: the influence of contraction velocity.

We compared changes in muscle fibre composition and muscle strength indices following a 10 week isokinetic resistance training programme consisting of fast (3.14 rad x s(-1)) or slow (0.52 rad x s(-1)) velocity eccentric muscle contractions. A group of 20 non-resistance trained subjects were assigned to a FAST (n = 7), SLOW (n = 6) or non-training CONTROL (n = 7) group. A unilateral training protocol targeted the elbow flexor muscle group and consisted of 24 maximal eccentric isokinetic contractions (four sets of six repetitions) performed three times a week for 10 weeks. Muscle biopsy samples were obtained from the belly of the biceps brachii. Isometric torque and concentric and eccentric torque at 0.52 and 3.14 rad x s(-1) were examined at 0, 5 and 10 weeks. After 10 weeks, the FAST group demonstrated significant [mean (SEM)] increases in eccentric [29.6 (6.4)%] and concentric torque [27.4 (7.3)%] at 3.14 rad x s(-1), isometric torque [21.3 (4.3)%] and eccentric torque [25.2 (7.2)%] at 0.52 rad x s(-1). The percentage of type I fibres in the FAST group decreased from [53.8 (6.6)% to 39.1 (4.4)%] while type IIb fibre percentage increased from [5.8 (1.9)% to 12.9 (3.3)%; P < 0.05]. In contrast, the SLOW group did not experience significant changes in muscle fibre type or muscle torque. We conclude that neuromuscular adaptations to eccentric training stimuli may be influenced by differences in the ability to cope with chronic exposure to relatively fast and slow eccentric contraction velocities. Possible mechanisms include greater cumulative damage to contractile tissues or stress induced by slow eccentric muscle contractions.

Adaptation, Physiological↗
PubMed2000

Postural control model interpretation of stabilogram diffusion analysis.

Collins and De Luca [Collins JJ. De Luca CJ (1993) Exp Brain Res 95: 308-318] introduced a new method known as stabilogram diffusion analysis that provides a quantitative statistical measure of the apparently random variations of center-of-pressure (COP) trajectories recorded during quiet upright stance in humans. This analysis generates a stabilogram diffusion function (SDF) that summarizes the mean square COP displacement as a function of the time interval between COP comparisons. SDFs have a characteristic two-part form that suggests the presence of two different control regimes: a short-term open-loop control behavior and a longer-term closed-loop behavior. This paper demonstrates that a very simple closed-loop control model of upright stance can generate realistic SDFs. The model consists of an inverted pendulum body with torque applied at the ankle joint. This torque includes a random disturbance torque and a control torque. The control torque is a function of the deviation (error signal) between the desired upright body position and the actual body position, and is generated in proportion to the error signal, the derivative of the error signal, and the integral of the error signal [i.e. a proportional, integral and derivative (PID) neural controller]. The control torque is applied with a time delay representing conduction, processing, and muscle activation delays. Variations in the PID parameters and the time delay generate variations in SDFs that mimic real experimental SDFs. This model analysis allows one to interpret experimentally observed changes in SDFs in terms of variations in neural controller and time delay parameters rather than in terms of open-loop versus closed-loop behavior.

Computer Simulation↗
PubMed2005

Maintenance of upright standing posture during trunk rotation elicited by rapid and asymmetrical movements of the arms.

Nine healthy subjects standing upright, initiated small, medium and large (S, M and L conditions, respectively) forward movements of their right (Rt) arm together with backward movements of their left (Lt) arm. They also performed medium-size movements while holding a 3 kg dumbbell in each hand (D condition). Movements started with the arm hanging alongside the body and ended when the shoulder reached a desired orientation. The arm and trunk movements were videotaped and recorded by accelerometers taped to the wrists, shoulders, and hips bilaterally. The torque around the vertical axis was measured using a force-plate on which the subjects stood. EMGs were recorded with surface electrodes bilaterally from the shoulder, trunk, and thigh muscles. Trajectories of the center of foot pressure were measured in additional experiments. In association with arm movements, there was a small counterclockwise (ccw: the Rt shoulder forward and the Lt backward) rotation of the trunk, followed by large alternate rotations of the trunk, first clockwise (cw) and subsequently ccw. The intervals from the hand acceleration to the shoulder and hip accelerations were, respectively, 0+/-15 ms (mean and S.D. for all subjects) and -17+/-15 ms. The force-plate showed initial cw and later ccw torques 63+/-41 ms after hand acceleration. The EMGs of the Rt hamstrings (Ham) and Lt rectus femoris (RFem) were followed by those of the Lt Ham and Rt RFem which, respectively preceded the alternate trunk rotations. The integrated EMGs and torques increased with increasing amplitude of arm movement and load. The integrated torques increased in the order of S, M, L, and D conditions. The integrated EMGs of the thigh muscles correlated with the integrated torques (medians: r=0.880, 0.696, 0.785, and 0.688, respectively, in the Rt Ham, Lt Ham, Rt RFem, and Lt RFem). The trajectories of the center of foot pressure showed variations, initially toward the Rt side and then the Lt side which, respectively coincided with the initial and later phases of the trunk rotations and the muscle activation. The trunk muscles were generally coactivated between the Rt and Lt muscles, and the integrated EMGs increased with increasing the integrated torques. Our results showed that alternate rotations of the upper trunk, produced by rapid arm movements, were transmitted to the hip in part due to cocontraction of trunk muscles, and each pair of hip joint muscles contributed to the maintenance of the standing posture by stabilizing the hip joints against alternating trunk rotations.

Adaptation, Physiological↗
PubMed2005

A new method for measuring passive length-tension properties of human gastrocnemius muscle in vivo.

The study of muscle growth and muscle length adaptations requires measurement of passive length-tension properties of individual muscles, but until now such measurements have only been made in animal muscles. We describe a new method for measuring passive length-tension properties of human gastrocnemius muscles in vivo. Passive ankle torque and ankle angle data were obtained as the ankle was rotated through its full range with the knee in a range of positions. To extract gastrocnemius passive length-tension curves from passive torque-angle data it was assumed that passive ankle torque was the sum of torque due to structures which crossed only the ankle joint (this torque was a 6-parameter function of ankle joint angle) and a torque due to the gastrocnemius muscle (a 3-parameter function of knee and ankle angle). Parameter values were estimated with non-linear regression and used to reconstruct passive length-tension curves of the gastrocnemius. The reliability of the method was examined in 11 subjects by comparing three sets of measurements: two on the same day and the other at least a week later. Length-tension curves were reproducible: the average root mean square error was 5.1+/-1.1 N for pairs of measurements taken within a day and 7.3+/-1.2 N for pairs of measurements taken at least a week apart (about 3% and 6% of maximal passive tension, respectively). Length-tension curves were sensitive to mis-specification of moment arms, but changes in length-tension curves were not. The new method enables reliable measurement of passive length-tension properties of human gastrocnemius in vivo, and is likely to be useful for investigation of changes in length-tension curves over time.

Adult↗
PubMed2006

Modelling the maximum voluntary joint torque/angular velocity relationship in human movement.

The force exerted by a muscle is a function of the activation level and the maximum (tetanic) muscle force. In "maximum" voluntary knee extensions muscle activation is lower for eccentric muscle velocities than for concentric velocities. The aim of this study was to model this "differential activation" in order to calculate the maximum voluntary knee extensor torque as a function of knee angular velocity. Torque data were collected on two subjects during maximal eccentric-concentric knee extensions using an isovelocity dynamometer with crank angular velocities ranging from 50 to 450 degrees s(-1). The theoretical tetanic torque/angular velocity relationship was modelled using a four parameter function comprising two rectangular hyperbolas while the activation/angular velocity relationship was modelled using a three parameter function that rose from submaximal activation for eccentric velocities to full activation for high concentric velocities. The product of these two functions gave a seven parameter function which was fitted to the joint torque/angular velocity data, giving unbiased root mean square differences of 1.9% and 3.3% of the maximum torques achieved. Differential activation accounts for the non-hyperbolic behaviour of the torque/angular velocity data for low concentric velocities. The maximum voluntary knee extensor torque that can be exerted may be modelled accurately as the product of functions defining the maximum torque and the maximum voluntary activation level. Failure to include differential activation considerations when modelling maximal movements will lead to errors in the estimation of joint torque in the eccentric phase and low velocity concentric phase.

Humans↗
PubMed2006

Effect of alendronate on endosseous implant integration: an in vivo study in rabbits.

PURPOSE: Alendronate sodium (Fosamax; Merck, Whitehouse Station, NJ) is a second-generation bisphosphonate used widely in osteopenic individuals for decreasing bone resorption and increasing bone density. The ability of alendronate to affect systemic bone remodeling raises natural questions about the drug's influence on dental implant osseointegration. Current knowledge regarding the effect of systemic bisphosphonates, specifically alendronate, on all 3 phrases of osseointegration is incomplete and only a few studies have started to investigate peri-implant bone responses to alendronate-coated implants. The purpose of this study was to determine the effect of systemic alendronate therapy on osseointegration of dental implants based on torque-removal values in rabbits. MATERIALS AND METHODS: Identical titanium dental implants were placed using a standardized surgical protocol in the bilateral distal femur and proximal tibia of 20 New Zealand white rabbits (79 implants total). One week before implant placement, 10 rabbits were given doses of alendronate and continued on weekly dosing for 5 weeks until euthanized. The other 10 rabbits were untreated controls. Torque-removal values were determined using a Tohinichi 15-BTG torque wrench (Tohinichi Mfg Co, Ltd, Tokyo, Japan) for all implants. RESULTS: Analysis of torque data showed no statistical differences between the alendronate and control groups in both femur and tibia sites. A statistically significant difference, however, was noted in torque removal values between femur and tibia sites regardless of drug or non-drug groups. CONCLUSIONS: In summary, orally dosed alendronate administration in rabbits had no significant effect on dental implant torque-removal values 6 weeks after endosseous placement in femur and tibia.

Alendronate↗
PubMed2001

The effect of weightbearing and external loading on anterior cruciate ligament strain.

A force balance between the ligaments, articular contact, muscles and body weight maintains knee joint stability. Thus, it is important to study anterior cruciate ligament (ACL) biomechanics, in vivo, under weightbearing conditions. Our objective was to compare the ACL strain response under weightbearing and non-weightbearing conditions and in combination with three externally applied loadings: (1) anterior-posterior shear forces, (2) internal-external torques, and (3) varus-valgus moments. A strain transducer was implanted on the ACL of 11 subjects. All joint loadings were performed with the knee at 20 degrees of flexion. A significant increase in ACL strain was observed as the knee made the transition from non-weightbearing to weightbearing. During anterior shear loading, the strain values produced during weightbearing were greater than those of the non-weightbearing knee (shear loads <40N). At higher shear loads, the strain values became equal. During axial torsion, an internal torque of 10Nm strained the ACL when the knee was non-weightbearing while an equivalent external torque did not. Weightbearing significantly increased ACL strain values in comparison to non-weightbearing with the application of external torques and low internal torques (<3Nm). The strains became equal for higher internal torques. For V-V loading, the ACL was not strained in the non-weightbearing knee. However, weightbearing increased the ACL strain values over the range of moments tested. These data have important clinical ramifications in the development of rehabilitation protocols following ACL reconstruction since weightbearing has been previously thought to provide a protective mechanism to the healing graft.

Adult↗
PubMed1999

The association between negative muscle work and pedaling rate.

The objective of this research was to use a pedal force decomposition approach to quantify the amount of negative muscular crank torque generated by a group of competitive cyclists across a range of pedaling rates. We hypothesized that negative muscular crank torque increases at high pedaling rates as a result of the activation dynamics associated with muscle force development and the need for movement control, and that there is a correlation between negative muscular crank torque and pedaling rate. To test this hypothesis, data were collected during 60, 75, 90, 105 and 120 revolutions per minute (rpm) pedaling at a power output of 260 W. The statistical analysis supported our hypothesis. A significant pedaling rate effect was detected in the average negative muscular crank torque with all pedaling rates significantly different from each other (p < 0.05). There was no negative muscular crank torque generated at 60 rpm and negligible amounts at 75 and 90 rpm. But substantial negative muscular crank torque was generated at the two highest pedaling rates (105 and 120 rpm) that increased with increasing pedaling rates. This result suggested that there is a correlation between negative muscle work and the pedaling rates preferred by cyclists (near 90 rpm), and that the cyclists' ability to effectively accelerate the crank with the working muscles diminishes at high pedaling rates.

Adult↗