Muscular coordination of knee motion during the terminal-swing phase of normal gait

Children with cerebral palsy often walk with diminished knee extension during the terminal-swing phase, resulting in a troublesome "crouched" posture at initial contact and a shortened stride. Treatment of this gait abnormality is challenging because the factors that extend the knee during normal walking are not well understood, and because the potential of individual muscles to limit terminal-swing knee extension is unknown. This study analyzed a series of three-dimensional, muscle-driven dynamic simulations to quantify the angular accelerations of the knee induced by muscles and other factors during swing. Simulations were generated that reproduced the measured gait dynamics and muscle excitation patterns of six typically developing children walking at self-selected speeds. The knee was accelerated toward extension in the simulations by velocity-related forces (i.e., Coriolis and centrifugal forces) and by a number of muscles, notably the vasti in mid-swing (passive), the hip extensors in terminal swing, and the stance-limb hip abductors, which accelerated the pelvis upward. Knee extension was slowed in terminal swing by the stance-limb hip flexors, which accelerated the pelvis backward. The hamstrings decelerated the forward motion of the swing-limb shank, but did not contribute substantially to angular motions of the knee. Based on these data, we hypothesize that the diminished knee extension in terminal swing exhibited by children with cerebral palsy may, in part, be caused by weak hip extensors or by impaired hip muscles on the stance limb that result in abnormal accelerations of the pelvis.     

Power output and work in different muscle groups during ergometer cycling

The aim of this study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling. Six healthy subjects pedalled a weight-braked bicycle ergometer at 120 watts (W) and 60 revolutions per minute (rpm). The subjects were filmed with a cine camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work at the hip, knee and ankle joint was calculated using a model based upon dynamic mechanics described elsewhere. The mean peak concentric power output was, for the hip extensors, 74.4 W, hip flexors, 18.0 W, knee extensors, 110.1 W, knee flexors, 30.0 W and ankle plantar flexors, 59.4 W. At the ankle joint, energy absorption through eccentric plantar flexor action was observed, with a mean peak power of 11.4 W and negative work of 3.4 J for each limb and complete pedal revolution. The energy production relationships between the different major muscle groups were computed and the contributions to the total positive work were: hip extensors, 27%; hip flexors, 4%; knee extensors, 39%; knee flexors, 10%; and ankle plantar flexors 20%.     

Power and work produced in different leg muscle groups when rising from a chair

The aim of this study was to determine the power output and work done by different muscle groups at the hip and knee joints during a rising movement, to be able to tell the degree of activation of the muscle groups and the relationship between concentric and eccentric work. Nine healthy male subjects rose from a chair with the seat at knee level. The moments of force about the hip and knee joints were calculated semidynamically. The power output (P) and work in the different muscle groups surrounding the joints was calculated as moment of force times joint angular velocity. Work was calculated as: work = f Pdt. The mean peak concentric power output was for the hip extensors 49.9 W, hip flexors 7.9 W and knee extensor 89.5 W. This power output corresponded to a net concentric work of 20.7 J, 1.0 J and 55.6 J, respectively. There was no concentric power output from the knee flexor muscles. Energy absorption through eccentric muscle action was produced by the hip extensors and hip flexors with a mean peak power output of 4.8 W and 7.4 W, respectively. It was concluded that during rising, the hip and knee muscles mainly worked concentrically and that the greatest power output and work were produced during concentric contraction of the knee and hip extensor muscles. There was however also a demand for eccentric work by the hip extensors as well as both concentric and eccentric work by the hip flexors. The knee flexor muscles were unloaded.     

Isokinetic strength and joint mobility asymmetries in oarside experienced oarsmen

The purpose of the present study was to investigate oarside and nonoarside lower extremity asymmetries in isokinetic strength and joint mobility of port and starboard oarsmen. Peak torques of right and left extensors and flexors were measured on isokinetic dynamometer at angular velocities of 60 and 180°·s-1 in 12 starboard (n = 12; training age 5.55 ± 0.52 years) and 14 port (n = 14; training age 6.09 ± 0.95 years) well-trained male rowers. Mobility of the hip, knee, and ankle joints was measured using the Myrin flexometer, a modification of the Leighton flexometer. The findings indicate that ports had a significantly higher peak torque in oarside right knee extensors at 60°·s-1 (p < 0.001) and 180°·s-1 (p < 0.01) compared to in the nonoarside left knee extensors. In a respective manner, starboards had a higher peak torque in left knee extensors at 60°·s-1 (p < 0.05) and 180°·s-1 (p < 0.05) compared to the right side. Right flexors peak torque was significantly higher in ports compared to that in starboards at 60°·s-1 (p < 0.05) and 180°·s-1 (p < 0.01). No significant difference between port and starboards in left knee flexors at either angular velocity was found. Both port and starboards exhibited a significantly higher hip (p < 0.01) mobility in oarside compared to in nonoarside. We conclude that sweep rowers develop a significantly higher flexion knee peak torque and hip mobility depending on oarside. Strength and mobility abnormalities may provide information for training and rehabilitation. Strengthening and stretching training programs to compensate for potential strength and mobility imbalance and thereby reducing the occurrence of injuries may be designed.     

Contributions of muscles to terminal-swing knee motions vary with walking speed

Many children with cerebral palsy walk with diminished knee extension during terminal swing, at speeds much slower than unimpaired children. Treatment of these gait abnormalities is challenging because the factors that extend the knee during normal walking, over a range of speeds, are not well understood. This study analyzed a series of three-dimensional, muscle-driven dynamic simulations to determine whether the relative contributions of individual muscles and other factors to angular motions of the swing-limb knee vary with walking speed. Simulations were developed that reproduced the measured gait dynamics of seven unimpaired children walking at self-selected, fast, slow, and very slow speeds (7 subjects×4 speeds=28 simulations). In mid-swing, muscles on the stance limb made the largest net contribution to extension of the swing-limb knee at all speeds examined. The stance-limb hip abductors, in particular, accelerated the pelvis upward, inducing reaction forces at the swing-limb hip that powerfully extended the knee. Velocity-related forces (i.e., Coriolis and centrifugal forces) also contributed to knee extension in mid-swing, though these contributions were diminished at slower speeds. In terminal swing, the hip flexors and other muscles on the swing-limb decelerated knee extension at the subjects’ self-selected, slow, and very slow speeds, but had only a minimal net effect on knee motions at the fastest speeds. Muscles on the stance limb helped brake knee extension at the subjects’ fastest speeds, but induced a net knee extension acceleration at the slowest speeds. These data—which show that the contributions of muscular and velocity-related forces to terminal-swing knee motions vary systematically with walking speed—emphasize the need for speed-matched control subjects when attempting to determine the causes of a patient's abnormal gait.     

Investigation of muscle tone in patients with Parkinson’s disease in unloading conditions

Parkinson’s disease (PD) is a progressive neurodegenerative disorder, the main symptoms of which are hypertonicity and difficulties emerging during performance of stepping movements due to increased muscle stiffness. Biomechanical (stiffness) and electrophysiological (shortening reaction, SR) characteristics of hip and shank muscles were examined in 25 patients with mild and moderate stages of PD (1 to 3 of Hoehn and Yahr Rating Scale, 61 ± 9 years) and 22 age-matched healthy controls in unloading leg conditions during passive flexion/extension of hip, knee, and ankle joints, as well as the changes in the tonic state of muscles under the influence of levodopa. The data obtained were compared with similar findings in healthy subjects. Essentially greater stiffness in all leg muscle groups (except foot extensors) was observed in patients with PD as compared to the healthy subjects. In patients with PD, SR values in hip and shank extensors as well as in foot flexors and extensors were essentially greater then in the healthy subjects. The medicine essentially reduced the stiffness of hip flexors and knee flexors and extensors. The SR persisted, although the frequency of its occurrence decreased in half of studied muscles, and a significant decrease in the SR value was observed in foot extensors. The medicine had no marked effect on the SR in the proximal muscles. Thus, the increased muscle stiffness in patients with PD manifests itself as distorted reactions to external disturbances and increased reflectory reactions of muscles.     

Functional morphology of the hindleg in two kangaroos Macropus giganteus and Aepyprymnus rufescens

In this study the structures in the hindleg of the kangaroo which are potentially available for jumping were examined. Specimens of two species, Macropus giganteus and Aepyprymnus rufescens, were examined and are described and compared. The basic pattern of the jump of the two species is similar. This is reflected anatomically by the fact that in both species the extensors of the hip, knee and ankle as a percentage of the total weight of the hindleg are greater than the flexors of the same joints. An additional similarity is that the biceps femoris and adductor magnus have the greatest share in the weight of the hip extensors. Furthermore the estimated total force of the hip, knee and ankle extensors and total moment of the hip and ankle extensors are always greater than the flexors of the same joints. However, the percentage of the hip and knee extensors, the absolute forces and moments of both the extensors and flexors and the range of movement especially of the hip and knee are always greater in M. giganteus than in A. rufescens. As well as these differences, the long tibia and the position of the knee in view of the hip may be important factors for the longer jump achieved by M. giganteus. In comparison A. rufescens has a anatomical construction which seems to be a compromise between walking and jumping.     

Contributions of muscles and passive dynamics to swing initiation over a range of walking speeds

Stiff-knee gait is a common walking problem in cerebral palsy characterized by insufficient knee flexion during swing. To identify factors that may limit knee flexion in swing, it is necessary to understand how unimpaired subjects successfully coordinate muscles and passive dynamics (gravity and velocity-related forces) to accelerate the knee into flexion during double support, a critical phase just prior to swing that establishes the conditions for achieving sufficient knee flexion during swing. It is also necessary to understand how contributions to swing initiation change with walking speed, since patients with stiff-knee gait often walk slowly. We analyzed muscle-driven dynamic simulations of eight unimpaired subjects walking at four speeds to quantify the contributions of muscles, gravity, and velocity-related forces (i.e. Coriolis and centrifugal forces) to preswing knee flexion acceleration during double support at each speed. Analysis of the simulations revealed contributions from muscles and passive dynamics varied systematically with walking speed. Preswing knee flexion acceleration was achieved primarily by hip flexor muscles on the preswing leg with assistance from biceps femoris short head. Hip flexors on the preswing leg were primarily responsible for the increase in preswing knee flexion acceleration during double support with faster walking speed. The hip extensors and abductors on the contralateral leg and velocity-related forces opposed preswing knee flexion acceleration during double support.     

Morphological and mechanical properties of muscle and tendon in highly trained sprinters

The purpose of this study was to investigate muscle and tendon properties in highly trained sprinters and their relations to running performance. Fifteen sprinters and 15 untrained subjects participated in this study. Muscle thickness and tendon stiffness of knee extensors and plantar flexors were measured. Sprinter muscle thickness was significantly greater than that of the untrained subjects for plantar flexors, but not for knee extensors (except for the medial side). Sprinter tendon stiffness was significantly lower than that of the untrained subjects for knee extensors, but not for plantar flexors. The best official record of a 100-m race was significantly correlated to the muscle thickness of the medial side for knee extensors. In conclusion, the tendon structures of highly trained sprinters are more compliant than those of untrained subjects for knee extensors, but not for plantar flexors. Furthermore, a thicker medial side of knee extensors was associated with greater sprinting performance.     

Relation between Peak Power Output in Sprint Cycling and Maximum Voluntary Isometric Torque Production

From a cycling paradigm, little has been done to understand the relationships between maximal isometric strength of different single joint lower body muscle groups and their relation with, and ability to predict PPO and how they compare to an isometric cycling specific task. The aim of this study was to establish relationships between maximal voluntary torque production from isometric single-joint and cycling specific tasks and assess their ability to predict PPO. Twenty male trained cyclists participated in this study. Peak torque was measured by performing maximum voluntary contractions (MVC) of knee extensors, knee flexors, dorsi flexors and hip extensors whilst instrumented cranks measured isometric peak torque from MVC when participants were in their cycling specific position (ISOCYC). A stepwise regression showed that peak torque of the knee extensors was the only significant predictor of PPO when using SJD and accounted for 47% of the variance. However, when compared to ISOCYC, the only significant predictor of PPO was ISOCYC, which accounted for 77% of the variance. This suggests that peak torque of the knee extensors was the best single-joint predictor of PPO in sprint cycling. Furthermore, a stronger prediction can be made from a task specific isometric task.     

Influence of bicycle seat tube angle and hand position on lower extremity kinematics and neuromuscular control: implications for triathlon running performance

We investigated how varying seat tube angle (STA) and hand position affect muscle kinematics and activation patterns during cycling in order to better understand how triathlon-specific bike geometries might mitigate the biomechanical challenges associated with the bike-to-run transition. Whole body motion and lower extremity muscle activities were recorded from 14 triathletes during a series of cycling and treadmill running trials. A total of nine cycling trials were conducted in three hand positions (aero, drops, hoods) and at three STAs (73°, 76°, 79°). Participants also ran on a treadmill at 80, 90, and 100% of their 10-km triathlon race pace. Compared with cycling, running necessitated significantly longer peak musculotendon lengths from the uniarticular hip flexors, knee extensors, ankle plantar flexors and the biarticular hamstrings, rectus femoris, and gastrocnemius muscles. Running also involved significantly longer periods of active muscle lengthening from the quadriceps and ankle plantar flexors. During cycling, increasing the STA alone had no affect on muscle kinematics but did induce significantly greater rectus femoris activity during the upstroke of the crank cycle. Increasing hip extension by varying the hand position induced an increase in hamstring muscle activity, and moved the operating lengths of the uniarticular hip flexor and extensor muscles slightly closer to those seen during running. These combined changes in muscle kinematics and coordination could potentially contribute to the improved running performances that have been previously observed immediately after cycling on a triathlon-specific bicycle.     

Biomechanical strategies for successful obstacle crossing with the trailing limb in older adults with medial compartment knee osteoarthritis

To investigate the biomechanical strategy adopted by older adults with medial compartment knee osteoarthritis (OA) for successful obstacle crossing with the trailing limb, and to discuss its implications for fall-prevention, 15 older adults with bilateral medial compartment knee OA and 15 healthy controls were recruited to walk and cross obstacles of heights of 10%, 20%, and 30% of their leg lengths. Kinematic and kinetic data were obtained using a three-dimensional (3D) motion analysis system and forceplates. The OA group had higher trailing toe clearance than the controls. When the trailing toe was above the obstacle, the OA group showed greater swing hip abduction, yet smaller stance hip adduction, knee flexion, and ankle eversion. They showed greater pelvic anterior tilt and toe-out angle. They also exhibited greater peak knee abductor moments during early stance and at the instant when the swing toe was above the obstacle, while a greater peak hip abductor moment was found during late stance. Smaller knee extensor, yet greater hip extensor moments, were found in the OA group throughout the stance phase. In order to achieve higher toe clearance with knee OA, particular joint kinematic and kinetic strategies have been adopted by the OA group. Weakness in the hip abductors and extensors in individuals with OA may be risk factors for tripping owing to the greater demands on these muscle groups during obstacle crossing by these individuals.     

Effect of squat depth and barbell load on relative muscular effort in squatting

ABSTRACT: Bryanton, MA, Kennedy, MD, Carey, JP, and Chiu, LZF. Effect of squat depth and barbell load on relative muscular effort in squatting. J Strength Cond Res 26(10): 2820-2828, 2012-Resistance training is used to develop muscular strength and hypertrophy. Large muscle forces, in relation to the muscle's maximum force-generating ability, are required to elicit these adaptations. Previous biomechanical analyses of multi-joint resistance exercises provide estimates of muscle force but not relative muscular effort (RME). The purpose of this investigation was to determine the RME during the squat exercise. Specifically, the effects of barbell load and squat depth on hip extensor, knee extensor, and ankle plantar flexor RME were examined. Ten strength-trained women performed squats (50-90% 1 repetition maximum) in a motion analysis laboratory to determine hip extensor, knee extensor, and ankle plantar flexor net joint moment (NJM). Maximum isometric strength in relation to joint angle for these muscle groups was also determined. Relative muscular effect was determined as the ratio of NJM to maximum voluntary torque matched for joint angle. Barbell load and squat depth had significant interaction effects on hip extensor, knee extensor, and ankle plantar flexor RME (p < 0.05). Knee extensor RME increased with greater squat depth but not barbell load, whereas the opposite was found for the ankle plantar flexors. Both greater squat depth and barbell load increased hip extensor RME. These data suggest that training for the knee extensors can be performed with low relative intensities but require a deep squat depth. Heavier barbell loads are required to train the hip extensors and ankle plantar flexors. In designing resistance training programs with multi-joint exercises, how external factors influence RME of different muscle groups should be considered to meet training objectives.     

Recovery Kinetics of Knee Flexor and Extensor Strength after a Football Match

We examined the temporal changes of isokinetic strength performance of knee flexor (KF) and extensor (KE) strength after a football match. Players were randomly assigned to a control (N = 14, participated only in measurements and practices) or an experimental group (N = 20, participated also in a football match). Participants trained daily during the two days after the match. Match and training overload was monitored with GPS devices. Venous blood was sampled and muscle damage was assessed pre-match, post-match and at 12h, 36h and 60h post-match. Isometric strength as well as eccentric and concentric peak torque of knee flexors and extensors in both limbs (dominant and non-dominant) were measured on an isokinetic dynamometer at baseline and at 12h, 36h and 60h after the match. Functional (KF_ecc/KE_con) and conventional (KF_con/KE_con) ratios were then calculated. Only eccentric peak torque of knee flexors declined at 60h after the match in the control group. In the experimental group: a) isometric strength of knee extensors and knee flexors declined (P<0.05) at 12h (both limbs) and 36h (dominant limb only), b) eccentric and concentric peak torque of knee extensors and flexors declined (P<0.05) in both limbs for 36h at 60°/s and for 60h at 180°/s with eccentric peak torque of knee flexors demonstrating a greater (P<0.05) reduction than concentric peak torque, c) strength deterioration was greater (P<0.05) at 180°/s and in dominant limb, d) the functional ratio was more sensitive to match-induced fatigue demonstrating a more prolonged decline. Discriminant and regression analysis revealed that strength deterioration and recovery may be related to the amount of eccentric actions performed during the match and athletes'' football-specific conditioning. Our data suggest that recovery kinetics of knee flexor and extensor strength after a football match demonstrate strength, limb and velocity specificity and may depend on match physical overload and players'' physical conditioning level.     

Joint contact loading in forefoot and rearfoot strike patterns during running

Research concerning forefoot strike pattern (FFS) versus rearfoot strike pattern (RFS) running has focused on the ground reaction force even though internal joint contact forces are a more direct measure of the loads responsible for injury. The main purpose of this study was to determine the internal loading of the joints for each strike pattern. A secondary purpose was to determine if converted FFS and RFS runners can adequately represent habitual runners with regards to the internal joint loading. Using inverse dynamics to calculate the net joint moments and reaction forces and optimization techniques to estimate muscle forces, we determined the axial compressive loading at the ankle, knee, and hip. Subjects consisted of 15 habitual FFS and 15 habitual RFS competitive runners. Each subject ran at a preferred running velocity with their habitual strike pattern and then converted to the opposite strike pattern. Plantar flexor muscle forces and net ankle joint moments were greater in the FFS running compared to the RFS running during the first half of the stance phase. The average contact forces during this period increased by 41.7% at the ankle and 14.4% at the knee joint during FFS running. Peak ankle joint contact force was 1.5 body weights greater during FFS running (p<0.05). There was no evidence to support a difference between habitual and converted running for joint contact forces. The increased loading at the ankle joint for FFS is an area of concern for individuals considering altering their foot strike pattern.     

Muscular contributions to hip and knee extension during the single limb stance phase of normal gait: a framework for investigating the causes of crouch gait

Crouch gait, a troublesome movement abnormality among persons with cerebral palsy, is characterized by excessive flexion of the hips and knees during stance. Treatment of crouch gait is challenging, at present, because the factors that contribute to hip and knee extension during normal gait are not well understood, and because the potential of individual muscles to produce flexion or extension of the joints during stance is unknown. This study analyzed a three-dimensional, muscle-actuated dynamic simulation of walking to quantify the angular accelerations of the hip and knee induced by muscles during normal gait, and to rank the potential of the muscles to alter motions of these joints. Examination of the muscle actions during single limb stance showed that the gluteus maximus, vasti, and soleus make substantial contributions to hip and knee extension during normal gait. Per unit force, the gluteus maximus had greater potential than the vasti to accelerate the knee toward extension. These data suggest that weak hip extensors, knee extensors, or ankle plantar flexors may contribute to crouch gait, and strengthening these muscles--particularly gluteus maximus--may improve hip and knee extension. Abnormal forces generated by the iliopsoas or adductors may also contribute to crouch gait, as our analysis showed that these muscles have the potential to accelerate the hip and knee toward flexion. This work emphasizes the need to consider how muscular forces contribute to multijoint movements when attempting to identify the causes of abnormal gait.     

The Isolated and Combined Effects of Menstrual Cycle Phase and Time-of-Day on Muscle Strength of Eumenorrheic Females

Diurnal variation in muscle performance has been well documented in the past few years, but almost exclusively in the male population. The possible effects of the menstrual cycle on human circadian rhythms have remained equivocal, particularly in the context of muscle strength. The purpose of the study was to analyze the isolated and combined effects of circamensal variation and diurnal changes on muscle strength. Eight eumenorrheic females (age 30 ± 5 yrs, height 1.63 ± 0.06 m and body mass 66.26 ± 4.6 kg: mean ± SD) participated in this investigation. Isokinetic peak torque of knee extensors and flexors of the dominant leg were measured at 1.05, 3.14 rad.s^?1 (through 90° ROM) at two times-of-day (06:00, 18:00 h) and five time points of the menstrual cycle (menses, mid-follicular, ovulation, mid-luteal, late luteal). In addition, maximum voluntary isometric contraction of knee extensors and flexors and electrically stimulated isometric contraction of the knee extensors were measured at 60° of knee flexion. Rectal temperature was measured during 30 min before the tests. There was a significant time-of-day effect on peak torque values for isometric contraction of knee extensors under electrical stimulation (P < 0.05). At 18:00 h, muscle force was 2.6% greater than at 06:00 h. The time-of-day effect was not significant when the tests were performed voluntarily without stimulation: effect size calculations indicated small differences between morning and evening for maximal voluntary isometric contraction and peak torque (at 1.05 rad.s^?1) for the knee extensors. A circamensal variation was observed for peak torque of knee flexors at 1.05 rad.s^?1, extensors at 3.14 rad.s^?1, and also isometric contraction of knee flexors, values being greatest at the ovulation phase. Interaction effects between time-of-day and menstrual cycle phase were not observed in any of the indices of muscle strength studied. The phase of the menstrual cycle seemed to have a greater effect than did the time-of-day on female muscle strength in this group of subjects. The present results suggest that peripheral rather than central mechanisms (e.g., motivation) are implicated in the diurnal variation of maximal isometric strength of women.     

Muscle activities of the lower limb during level and uphill running

This study aimed to compare the muscle activities of the lower limb during overground level running (LR) and uphill running (UR) by using a musculoskeletal model. Six male distance runners ran at three running speeds (slow: 3.3 m/s; medium: 4.2 m/s; and high: 5.0 m/s) on a level runway and a slope of 9.1% grade in which force platforms were mounted. A musculoskeletal leg model and optimization were used to estimate the muscle activation and muscle torque from the joint torque of the lower limb calculated by the inverse dynamics approach. At high speed, the activation and muscle torque of the muscle groups surrounding the hip joints, such as the hamstrings and iliopsoas, during the recovery phase were significantly greater during UR than during LR. At all the running speeds, the knee extension torque by the vasti during the support phase was significantly smaller during UR. Further, the hip flexion and knee extension torques by the rectus femoris during UR were significantly greater than those during LR at all the speeds; this would play a role in compensating for the decrease in the knee extension torque by the vasti and in maintaining the trunk in a forward-leaning position. These results revealed that the activation and muscle torque of the hip extensors and flexors were augmented during UR at the high speed.