Range Of Knee Angles Research Articles

Proposed model of botulinum toxin-induced muscle weakness in the rabbit

Osteoarthritic patients show only a weak association between radiographic signs of joint disease and joint pain and disability. Conversely, muscle weakness is one of the earliest and most common symptoms of patients with osteoarthritis (OA). However, while many experimental models of osteoarthritis include a component of muscular weakness, no model has isolated this factor satisfactorily. Therefore, the purpose of this study was to develop and validate an experimental animal model of muscle weakness for future use in the study of OA. Botulinum Type-A toxin (BTX-A) was uni-laterally injected into the quadriceps musculature of New Zealand white rabbits (3.5 units/kg). Isometric knee extensor torque at a range of knee angles and stimulation frequencies, and quadriceps muscle mass, were quantified for control animals, and at one- and six-months post-repeated injections, in both, the experimental and the contralateral hindlimb. Ground reaction forces were measured in all animals while hopping across two force platforms. Isometric knee extension torque and quadriceps muscle mass was systematically decreased in the experimental hindlimb. Vertical ground reaction forces in the push off phase of hopping were also decreased in the experimental compared to control hindlimbs. We conclude that BTX-A injection into the rabbit musculature creates functional and absolute muscle weakness in a reproducible manner. Therefore, this model may be used to systematically study the possible effects of muscle weakness on joint degeneration, either as an isolated intervention, or in combination with other interventions (anterior cruciate ligament transection, meniscectomy) known to create knee joint degeneration.

Proposed model of botulinum toxin-induced muscle weakness in the rabbit

Osteoarthritic patients show only a weak association between radiographic signs of joint disease and joint pain and disability. Conversely, muscle weakness is one of the earliest and most common symptoms of patients with osteoarthritis (OA). However, while many experimental models of osteoarthritis include a component of muscular weakness, no model has isolated this factor satisfactorily. Therefore, the purpose of this study was to develop and validate an experimental animal model of muscle weakness for future use in the study of OA. Botulinum Type-A toxin (BTX-A) was uni-laterally injected into the quadriceps musculature of New Zealand white rabbits (3.5 units/kg). Isometric knee extensor torque at a range of knee angles and stimulation frequencies, and quadriceps muscle mass, were quantified for control animals, and at one- and six-months post-repeated injections, in both, the experimental and the contralateral hindlimb. Ground reaction forces were measured in all animals while hopping across two force platforms. Isometric knee extension torque and quadriceps muscle mass was systematically decreased in the experimental hindlimb. Vertical ground reaction forces in the push off phase of hopping were also decreased in the experimental compared to control hindlimbs. We conclude that BTX-A injection into the rabbit musculature creates functional and absolute muscle weakness in a reproducible manner. Therefore, this model may be used to systematically study the possible effects of muscle weakness on joint degeneration, either as an isolated intervention, or in combination with other interventions (anterior cruciate ligament transection, meniscectomy) known to create knee joint degeneration.

Damage to the human quadriceps muscle from eccentric exercise and the training effect

Nine participants performed two bouts of a step exercise, during which the quadriceps muscle of one leg acted eccentrically. Before and after the exercise, isokinetic torque was measured over a range of knee angles to determine the optimum angle for torque. Immediately after the first bout of exercise, the quadriceps showed a significant (P < 0.05) shift of 15.6 +/- 1.4 degrees (mean +/-sx) of its optimum angle in the direction of longer lengths, suggesting the presence of damage. A drop in peak torque, together with delayed soreness and swelling, confirmed that damage to muscle fibres had occurred. After the second bout of exercise, 8 days later, the shift in optimum angle was 10.4 +/- 1.0 degrees, which was significantly less than after the first bout (P < 0.05). Other indicators of damage were also reduced. In addition, the muscle exhibited a sustained shift in optimum angle (3.4 +/- 0.9 degrees), suggesting that some adaptation had taken place after the first bout of exercise. We conclude that muscles like the quadriceps can show evidence of damage after a specific programme of eccentric exercise, followed by an adaptation response. This is despite the fact that the quadriceps routinely undergoes eccentric contractions in everyday activities.

The effect of joint angle on the timing of muscle contractions elicited by neuromuscular electrical stimulation

Neuromuscular electrical stimulation was used to evoke isometric knee extension contractions in seven individuals with spinal cord injury (SCI) and the time for knee extension torque to rise and fall was measured across a range of knee angles. The stimulated muscles took more than twice as long to develop 50% of maximum torque at an angle of 15 degrees, compared to an angle of 90 degrees. This time difference comprised both an increased delay before torque rose above resting levels (31 +/- 3 ms at 90 degrees, 67 +/- 24 ms at 15 degrees), and a prolonged duration over which torque was rising (72 +/- 14 ms at 90 degrees, 140 +/- 62 ms at 15 degrees). There was no change, however, in the time taken for torque to fall after cessation of stimulation at different knee angles (58 +/- 5-ms delay, 60 +/- 11-ms fall time). The difference in torque rise time with joint angle has implications for modeling functional activities that differ greatly in their joint angles. This study provides regression equations whereby activation times for the quadriceps muscles of individuals with SCI can be predicted for specific angles of knee flexion.

EFFICIENCY OF BELOW-KNEE AMPUTEE CYCLING

Cycling has increased in popularity for lower extremity amputees seeking increased physical activity. Remarkably, the world records by amputee cyclists are about 84% as fast as non-amputees in most velodrome events. Fundamental research about the physiology and biomechanics of amputee cyclists is lacking. Such information is needed to optimize equipment/prosthetic design and training. PURPOSE To determine the efficiency of cycling in simulated unilateral and bilateral below-knee (BK) amputee cyclists. METHODS Unilateral and bilateral BK amputee biomechanics were simulated in 5 male and 5 female trained non-amputee cyclists. Simulation was achieved by attaching the shoe to the pedal via a heel extension and pedal cleat. This design mimics the shaft prostheses used by most competitive amputee cyclists and elimnates ankle motion during the pedal stroke. Adjustments were made to the height and the fore-aft position of the heel extension to match the cyclists' knee angle range of motion during their normal pedal stroke. Subjects completed 3 randomized pedaling conditions: normal, simulated unilateral BK, and simulated bilateral BK. After familiarization on the Lode cycle ergometer, each condition began at 75W and increased by 25W every 5 minutes. All subjects completed the 150W stage. Rates of oxygen consumption (VO2) were measured for the final 3 minutes of each stage. A repeated measure ANOVA was used to determine differences between the 3 conditions. RESULTS For stages 75–150W no differences were observed in VO2 between the 3 conditions (p = .92). CONCLUSION Simulated amputee mechanics in healthy cyclists did not change pedaling efficiency. Thus, the slower race performance of amputee cyclists appear not to be due to poor efficiency. The next step is to measure the efficiency of true amputee cyclists. Finally, these data shed doubt on the common notion that the efficiency of pedaling can be improved by technique changes.

THE ADDITION OF SARCOMERES IN SERIES IS THE MAIN PROTECTIVE MECHANISM FOLLOWING ECCENTRIC EXERCISE

Sore muscles following unaccustomed eccentric exercise is a common experience. One remarkable aspect of this is the rapid training. A single bout of exercise can provide significant protection against muscle damage and soreness from subsequent bouts. Several studies have shown that such training also increases the optimum muscle length and/or the number of sarcomeres. The present study aimed to test whether this accounts for all the protection. Rats were trained for up to 30 minutes per day on a treadmill, either inclined to 16° (concentrically biased exercise) or declined to 16° (eccentrically biased exercise) for one week. The decline rats were found to have smaller optimum knee angles, or longer muscle lengths, for torque generation by vastus intermedius muscles than the incline rats. When test eccentric contractions were given over the same range of knee angles for each training group, the decline rats showed less damage. When the differences in the optimum length were accounted for and the eccentric contractions were given over the same portion of the torque angle curve, there was no difference between the two groups in the amount of damage that they suffered, suggesting that the shift in optimum was responsible for all of the protection.

Co-activation of quadriceps and hamstring muscles during concentric and eccentric isokinetic exercise

The purpose of this study was to investigate co-activation of the quadriceps and hamstring musculature during concentric and eccentric isokinetic actions at 30° s -I. Eight female sedentary subjects performed maximal concentric and eccentric knee flexion/extension actions on an isokinetic dynamometer while simultaneous recordings of moment, joint position and agonist/antagonist electromyographic (EMG) activity from the rectus femoris and semitendinosus muscles were computer processed. Mean integrated electromyographic (IEMG) activity for agonist and antagonist muscle groups and mean moment data were calculated for three discrete knee angle ranges; outer (25-34°), mid (45-54°) and inner (65-74°) for both concentric and eccentric actions. Individual IEMG activity was corrected to account for background activity in the unstressed muscle at 30°, 50° and 70° of knee flexion/extension. The results of this study show that under concentric and eccentric actions the hamstrings were more active during knee extension than the quadriceps were during knee flexion at all angle ranges studied. The corrected mean per cent IEMG activity of the co-contracting hamstrings throughout the joint range were 14 and 21 % for concentric and eccentric actions respectively, for co-contracting quadriceps these values were 2.5 and 3.5% respectively. All per cent IEMG values were expressed as a percentage of the same muscle group and action (shortening/lengthening) during agonist action. No significant difference was seen between concentric and eccentric co-contraction per cent IEMG activity at any knee angle range studied. The data suggests that the hamstrings are used to a much greater extent than the quadriceps for limb deceleration and that in particular, hamstring antagonist muscle tension should be considered when analysing agonist quadriceps isokinetic moment curves.

Identification of quadriceps-shank dynamics using randomized interpulse interval stimulation

Model structures for artificially stimulated paralyzed muscle-limb system dynamics were developed and experimentally evaluated in paraplegic patients. The examined system consisted of the quadriceps, electrically stimulated using surface electrodes, and a freely swinging shank. The interpulse interval of the stimulation sequence was randomized to obtain persistent system excitation. The outputs of the system were the angular position, velocity, and acceleration, measured by externally mounted sensors. The authors especially report on model identification of the active quadriceps dynamics and the angle prediction performance of the total quadriceps-shank model. Second-order modeling of the twitch dynamics with delay did not significantly improve the prediction results in comparison to a zero-order model with delay (/spl alpha/=0.05). Nonlinear torque-angle and torque-angular velocity relations in combination with a zero-order model (with delay) only slightly improved the prediction results for large prediction intervals (/spl alpha/=0.05). The delay between stimulation input and resulting knee joint acceleration appeared to be joint angle dependent and was estimated to be largest in the knee angle range near knee extension, i.e., when quadriceps muscle is shortest.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Speed-related changes in hindlimb intersegmental dynamics during the swing phase of cat locomotion

To determine speed-related changes in hindlimb motion that might account for the mutability of bifunctional (hip extensor/knee flexor) muscle activity during the E1 phase of swing, we studied hip and knee joint kinematics and kinetics during swing over a ten-fold increase in locomotor speed (0.35 to 3.5 m/s). Three cats were filmed (100 frames/s) while locomoting on a motorized treadmill; kinematics were analyzed for the entire step cycle and kinetics for the swing phase. During swing, angular excursions at the hip and knee joints were similar for walking and trotting, but hip flexion and extension were significantly less after the transition from trot to gallop, while knee-angle range of motion increased during gallop phases E1, E2, and E3. During swing, knee-extension velocity peaked early in E1 and increased linearly with speed, while hip-flexion velocity peaked late in the flexion (F) phase and also increased linearly, but decreased precipitously at the trot-gallop transition and remained constant as speed of galloping increased. Muscle torque directions during E1, flexor at the knee and extensor at the hip, were consistent with the proposed role of bifunctional posterior thigh muscles to decelerate thigh and leg segments for paw contact. At the knee joint, muscle torque during E1 counteracted a large interactive torque due to leg angular acceleration; the magnitudes of both torques were speed related with maximal values at the fastest speed tested (3.5 m/s). At the hip joint, muscle torque during E1 also counteracted a large interactive torque due to leg angular acceleration; the magnitudes of these two torques were speed related during the walk and trot, and like hip flexion velocity, decreased at the trot-gallop transition. Our data on speed-related changes in hindlimb dynamics suggest that the E1 burst amplitude (and perhaps duration) of posterior thigh muscles will be speed related during the walk and trot. After the trot-gallop transition at about 2.5 m/s, the recruitment of these bifunctional muscles may decline due to the changes in hindlimb dynamics. Because activity of these muscles counteracts interactive torques primarily related to leg angular acceleration, we suggest that motion-related feedback decoding this action may be important for regulating recruitment during E1.

Passive resistance of the human knee: The effect of remobilization

Changes of circumferential dimensions and passive resistance of the human knee caused by immobilization, were studied during remobilization. Patients immobilized with a long leg cast after tibial fractures or ligamentous injuries were studied immediately after removal of the cast and after mean periods of 18, 36 and 81 days of remobilization. Immobilization resulted in a decrease of circumferential dimensions. The difference in mid-thigh circumference between the immobilized and the unaffected leg was still present after 81 days of remobilization both for the patients with tibial fractures and for the patients with ligamentous lesions. An increase of midpatellar circumference was present exclusively in the patients with ligamentous lesions at all four testing dates, indicating that this is an effect of the ligamentous lesion and not of immobilization per se. Variables of the hysteresis diagrams, resulting from sinusoidal movement of the knee at a range of knee angles, were used to quantify passive resistance of the knee in the flexion-extension plane (the muscles crossing the knee are inactive). Variables related to the elastic storage and release of energy, and variables related to energy dissipation were discerned. During remobilization the increased resistance to flexion (shown by the variables related to the elastic storage of energy), as found immediately after removal of the cast, disappears and the resistance becomes identical to the resistance of the unaffected leg. This may indicate a rapid readaptation of the length of ventral structures (shortened due to immobilization in a shortened position) to almost normal values. The variables related to energy dissipation, which do not differ between the two legs immediately after immobilization, are low in comparison with the unaffected knee during the whole remobilization period studied, indicating a remaining atrophy (as is also shown by the still decreased aircumference of the lower limb). All resistance variables are still lower at the last date of testing when the knee is extended. The remobilization period studied was not long enough to achieve complete restoration of the dimensions of the lower limb and full return of normal passive resistance of the knee.