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PubMed2007

Knee-muscle activation during landings: developmental and gender comparisons.

PURPOSE: This study determined anteroposterior knee-joint muscle activation differences among children and adult males and females landing from a self-initiated vertical jump (VJ) under normal and offset-target conditions to further understand physical maturation's influence on anterior cruciate ligament (ACL) injury risk. METHODS: Fifty-five recreationally active volunteer subjects grouped by age (children = 9.5 +/- 0.9 yr; adult = 23.9 +/- 2.8 yr) and gender (females = 28; males = 27) completed motion analysis, ground reaction force, and surface electromyography (SEMG) data collection during a two-footed landing under straight (midline-target) and offset-target (adult = 45.7 cm; child = 30.5 cm) conditions. Target height was 50% of maximum VJ height. Co-contraction ratios (CCR) (hamstrings (HAMS)/vastus medialis (VM) activity) from normalized SEMG root mean squares were analyzed in the prelanding (PRE) (100 ms before initial contact (IC)), reflexive (REF) (100 ms after IC), and voluntary (VOL) (end of REF to maximum knee flexion) muscle activity phases. Repeated-measures statistical analyses determined significant gender, physical maturation, and target differences (P < 0.05) in CCR and associated HAMS and VM activity across landing phases. RESULTS: A significant interaction (P < 0.0001) indicated similar CCR for children and adults during the REF and VOL phases, but during the PRE phase adult CCR (619.04 + 52.01) were two times greater than children's (308.32 +/- 51.04). Significantly more HAMS activity, not less VM activity, increased adult PRE-CCR. Gender and target CCR differences were absent. CONCLUSIONS: Children's decreased preparatory co-contraction about the knee does not seem to be linked to increased ACL injury risk. Thus, adults may strive for preparatory co-contraction levels about the knee that permit adaptability to varied landing tasks.

Adolescent↗
PubMed1995

Walking, running, and sprinting: a three-dimensional analysis of kinematics and kinetics.

Just as in running, the two-joint muscles acting at the hip and at the knee work to transfer energy efficiently between body segments. This can be seen in Figure 12. The powers at the hip and knee are overlaid to show that when power is generated at the hip, it is absorbed at the knee and vice versa. For example, a concentric contraction of the hamstrings proximally at the hip is coupled with an eccentric contraction at the knee just prior to initial contact in terminal swing. The rectus femoris functions in a similar way but in an opposite direction in initial swing. For the three conditions discussed, the relative contribution of work occurring at each joint is different. Figure 13 shows that the muscles about the ankle are the most important source of work in walking and that the knee musculature does not significantly contribute to the work done for walking. In walking, the knee is felt to be important for the smoothing of gait. The quadriceps are a much more important source of energy at the knee in both running and sprinting, as can be seen in Figure 13. Finally, the hip musculature becomes the dominant source of work in sprinting in our group of untrained subjects with significant contributions from both the hip flexors and extensors. One would expect that the relative importance of each of the muscle groups about each of these joints in terms of sources of energy might change with training. The intent of this work was to evaluate the three conditions of walking, running, and sprinting. I hope that it will stimulate further interest and research in this area in order to come to a greater understanding of human locomotion. As more knowledge and experience are gained, the motion analysis lab will be able to offer insight into training strategies, injury prevention, and the treatment of pathologic running and sprinting conditions.

Adolescent↗
PubMed1998

Gait analysis before or after varus osteotomy of the femur for hip osteoarthritis.

SUMMARY OF BACKGROUND: Intertrochanteric varus osteotomy of the femur for hip osteoarthritis is expected to bring improved congruity and increased weight-bearing surface area of the hip joint. Before surgery, we usually make a tracing on a paper using an anteroposterior roentgenogram of the hip to simulate the operating procedures and obtain better conditions in the hip. Nevertheless, there have been some cases in which this procedure does not provide satisfactory postoperative results in terms of relief of pain or locomotion, with long-term limp due to weakness of the hip abductor muscle group and shortening of the leg. OBJECTIVES: To confirm if the improved congruity and increased covering of the weight-bearing surface area obtained by varus osteotomy can be actually reproduced during walking, and to evaluate the kinetic mechanism of the effects of this procedure using gait analysis. METHODS: We measured the strength ratio of the hip abductor muscles as the percent of the opposite side, and analyzed the pelvic movement and data of dynamic electromyography (EMG) recorded during locomotion in 24 female patients who underwent unilateral intertrochanteric varus osteotomy of the femur for hip osteoarthritis, 30 non-surgically-treated female patients with hip osteoarthritis, and 54 healthy women. In the operated patients, the roentgenograms obtained during one-legged stance on the affected side disclosed that 10 were positive for Trendelenburg's phenomenon (T(+) group) and 14 were negative for Trendelenburg's phenomenon (T(-) group). All subjects walked with bare feet at a comfortable pace on a walkway containing a force plate. Photo switches were placed in a walkway to measure the gait velocity and to determine the stance phase time of one gait cycle. Frontal and sagittal trajectories of body surface markers for computerized joint-angle motion analysis were acquired using the Quick-MAG system. EMG data for the gluteus maximus, gluteus medius, tensor fascia latae, and lateral hamstrings recorded using surface electrodes were integrated to quantify as the percent of maximum voluntary contraction (% MVC). RESULTS: This study disclosed that the stance phase time was shorter and the strength ratio of the hip abductor muscles was lower in the operated patients than those in the other 2 groups, and the change of the pelvic obliquity was smaller and the % MVC of the gluteus medius and tensor fascia latae were greater than those in the normal subjects. The change of the pelvic tilt showed the same pattern with those of the pelvic obliquity. The T(+) group showed decreased strength ratio of the hip abductor muscles and increased % MVC for the gluteus medius and the tensor fascia latae compared to the T(-) group, but the changes of both the pelvic obliquity and pelvic tilt did not significantly differ in the 2 groups. CONCLUSION: This study showed the postoperative reappearance of the simulated conditions in the hip before varus osteotomy of the femur, providing evidence that the pelvis was horizontally maintained during walking due to decreased stance phase time and increased performance of the hip abductor muscles after this procedure.

Adult↗
PubMed2000

An integrated biomechanical analysis of high speed incline and level treadmill running.

PURPOSE: Recent sprint training regimens have used high-speed incline treadmill running to provide enhanced loading of muscles responsible for increasing forward running speed. The goal of this study was to document the joint kinematics, EMG, and swing-phase kinetics of incline treadmill running at 4.5 m x s(-1) with a 30% grade, and compare these data to that of level running under similar conditions. METHODS: Sagittal plane video (200 Hz) and EMG from eight lower extremity muscles were recorded during each of three locomotion conditions: incline running at 4.5 m x s(-1) and 30% grade (INC), level running at 4.5 m x s(-1) (LSS), and level running at the same stride frequency as INC (LSSF). A rigid body model was used to estimate net muscle power and work values at the hip, knee, and ankle during swing. Timing and amplitude of EMG signals for each muscle relative to footstrike were compared between conditions. RESULTS: Stride frequency and percentage of stride spent in stance were significantly higher during INC (1.78 Hz; 32.8%) than in the LSS (1.39 Hz; 28.8%) condition. Stride frequency played an important role, as most measures were more similar between INC and LSSF. Extensor range of motion of all joints during push-off was higher for INC. During INC, average EMG amplitude of the gastrocnemius, soleus, rectus femoris, vastus lateralis, and gluteus maximus were higher during stance, whereas the hamstrings activity amplitudes were lower. Average power and energy generated during hip flexion and extension in the swing phase were greatest during INC. CONCLUSIONS: These data suggest that compared with LSSF and LSS, INC provides enhanced muscular loading of key mono- and bi-articular muscles during both swing and stance phases.

Adult↗
PubMedDate not supplied

Increasing hamstring flexibility decreases lower extremity overuse injuries in military basic trainees.

The purpose of this intervention study was to prove that increasing flexibility of the hamstring musculotendinous unit would decrease the number of lower extremity overuse injuries that occur in military infantry basic trainees. Two different companies going through basic training at the same time were used. Hamstring flexibility was checked at the beginning and at the end of the 13-week infantry basic training course. The control company (N = 148) proceeded through normal basic training. The intervention company (N = 150) followed the same program but added three hamstring stretching sessions to their already scheduled fitness program. All subsequent lower extremity overuse injuries were recorded through the troop medical clinic. Hamstring flexibility increased significantly in the intervention group compared with the control group. The number of injuries was also significantly lower in the intervention group. Forty-three injuries occurred in the control group for an incidence rate of 29.1%, compared with 25 injuries in the intervention group for an incidence rate of 16.7%. Thus, in this study, the number of lower extremity overuse injuries was significantly lower infantry basic trainees with increased hamstring flexibility.

Adult↗
PubMed1990

Disability in anterior cruciate ligament insufficiency. An analysis of 19 untreated patients.

We analyzed the knee function in 19 consecutive patients with chronic instability after an anterior cruciate ligament rupture. Muscle strength, standing balance, activity level, functional knee score, and a performance test were evaluated. Reduced quadriceps muscle strength compared with the noninjured limb was associated with reduced performance as measured by the one-leg hop test and the Lysholm knee score. No weakness in the hamstrings was found. The patients had impaired standing balance with increased body sway in the frontal plane when standing on both the injured and noninjured limb.

Adolescent↗
PubMed1996

Comparison of stretching with ice, stretching with heat, or stretching alone on hamstring flexibility.

OBJECTIVE: To investigate the efficacy of stretching with ice for increasing hamstring flexibility. DESIGN AND SETTING: Supine hamstring flexibility was measured before and after subjects accomplished a 20-minute hamstring stretching routine. Two groups of eight subjects accomplished the routine using one of two modalities. A control group (n = 8) accomplished the routine without a modality. The measurements were compared. SUBJECTS: Twenty-four male collegiate baseball players. MEASUREMENTS: Heat or ice applied to the hamstring. RESULTS: We found differences in the responses among subject groups. Supine hamstring flexibility after stretching with ice was greater than both stretching with heat and stretching alone. Scores after stretching with heat and stretching alone were not different. CONCLUSIONS: The results of our investigation suggest that the application of ice may provide enhanced short-term improvements in hamstring flexibility over heat or stretching alone. Further research is necessary to investigate the possible mechanisms for these improvements and to determine whether similar results can be obtained with other muscle groups.

Journal Article↗
PubMed2000

Effect of ankle position fixation on peak torque and electromyographic activity of the knee flexors and extensors.

The purpose of this study was to examine the effect of ankle position fixation on peak torque (PT) and electromyographic (EMG) activity of knee-joint muscles during isokinetic testing. Twelve female athletes performed isokinetic knee flexion and extension at 60 degrees and 180 degrees/s under two conditions: with the ankle fixed in a position of plantarflexion and with the ankle fixed in a position of dorsiflexion. Bipolar surface electrodes were placed on the vastus lateralis, vastus medialis, biceps femoris, medial hamstrings, and the lateral head of the gastrocnemius for determination of the root mean square of the EMG (rmsEMG) and the median frequency of the EMG (mfEMG). No significant differences in knee extensor PT were noted in either ankle position for each velocity tested. Significant differences were noted, however, in knee flexor PT (p < 0.05) at both 60 degrees and 180 degrees/s, with the greatest PT observed with the ankle fixed in dorsiflexion. Neither quadriceps, hamstrings, nor gastrocnemius rmsEMG activity was affected by ankle position; however, there was a significant difference in mfEMG for the gastrocnemius, with higher frequencies observed with the ankle fixed in plantarflexion (p < 0.01). These results suggest that ankle position effects knee flexor PT during open chain isokinetic movements. The reason for decreased knee flexor PT with the ankle fixed in plantarflexion is probably due to the gastrocnemius muscle being in a too shortened position, thereby preventing it from effectively producing force at the knee joint.

Adult↗
PubMed2002

Muscle torques in total knee arthroplasty with subvastus and parapatellar approaches.

The current study was designed to compare muscle torques when using the subvastus and parapatellar approaches for unilateral total knee arthroplasty. Twelve female patients had unilateral total knee arthroplasty with the subvastus approach from January 1997 to June 1998. The historic control group consisted of 16 female patients who had unilateral total knee arthroplasty with the parapatellar approach from July 1994 to January 1997. Six and 12 months after surgery, a Cybex dynamometer was used to measure isometric and isokinetic muscle strength. Two parameters were used to compare the two approaches, the first parameter was the difference in peak torque between the surgically treated knee and the baseline value for the healthy knee, and the second parameter was the hamstring to quadriceps peak-torque ratio, again using the value for the healthy knee as baseline. The subvastus approach resulted in an initial higher peak torque in the quadriceps 6 months after surgery, but this difference became insignificant 12 months postoperative. Using the subvastus approach, the hamstring to quadriceps peak-torque ratio reached the normal range (0.50-0.80) sooner than was the case using the parapatellar approach. There is a phenomenon of cross adaptation of the untreated knee to the surgically treated knee, and knees operated on by the subvastus approach showed functional recovery at an earlier date than those operated on by the parapatellar approach.

Adult↗
PubMed2006

Muscular compensation and lesion of the anterior cruciate ligament: contribution of the soleus muscle during recovery from a forward fall.

BACKGROUND: Knee stability following an anterior cruciate ligament lesion has been widely studied. Only recent studies focused on the contribution of the soleus muscle. Our purpose was to characterize the dynamic and muscular activity of balance recovery in healthy subjects and patients with an anterior cruciate ligament rupture. The role of the soleus was investigated in the ipsilateral compensation developed to stabilize the knee and in the contralateral compensation to recover balance. METHODS: Twelve anterior cruciate ligament deficient patients, ten anterior cruciate ligament repaired patients and 14 control subjects were recorded during a forward fall involving stepping to recover balance. FINDINGS: The dynamic of the centre of gravity remained normal when compared to the control group regardless of the treatment, suggesting an adapted compensation to knee instability in this situation. A bilateral increase in soleus activity was related to an increased duration in the balance recovery process in all patients. Patients used one of two strategies to recover balance regardless of the treatment: reducing the step length, involving an early recruitment of the soleus before heel contact, or anticipating braking with a similar step length requiring a predominant activity of the hamstrings. INTERPRETATIONS: These results suggest that bilateral activity of the soleus is involved to compensate for instability and highlight the contribution of the soleus to rehabilitation after an anterior cruciate ligament lesion, not only as a compensatory muscle acting at the knee level but also at a higher level in the bilateral control of stance.

Accidental Falls↗
PubMed2004

Reproducibility of electromyography and ground reaction force during various running techniques.

This study examined the validity of the assumption of electromyographic (EMG) and vertical ground reaction force (GRF) parameter reproducibility during running at different velocities and stride frequencies. Each of 12 female long distance runners ran on a treadmill in combinations of three velocities (2.5, 3.0 and 3.5 m/s) and three stride frequencies (preferred, +/-10% from preferred). Seven parameters from the GRF and five parameters from the EMG signals from five muscles of the lower extremity were evaluated (1000 Hz). The GRF was analysed by a pressure measuring insoles. A total number of three trials for each running condition were recorded. GRF parameters during all running conditions showed high intraclass correlation coefficients (ICC average 0.87). The ICC of the EMG parameters of gastrocnemius medialis and lateralis were high (r>0.69 in 73% of the data), while those for vastus lateralis (22%), hamstrings (42%) and tibialis anterior (51%) were clearly lower. The results revealed that GRF parameters were reproducible during all running techniques indicating that a single trial would provide reproducible GRF-data. The reproducibility of the EMG parameters was not influenced by the running technique but dependent on the parameter itself and on the muscle studied.

Adult↗
PubMed2006

Relationships among measures of knee musculoskeletal impairments, gross motor function, and walking efficiency in children with cerebral palsy.

PURPOSE: The study was designed to determine whether relationships exist among knee muscle spasticity, isometric knee muscle strength, knee muscle balance, gross motor function, and walking efficiency in children with spastic cerebral palsy and to evaluate the relative contributions of impairment measures to functional outcome measures. METHODS: Twenty-seven children with spastic diplegic cerebral palsy participated. Knee muscle strength and spasticity were measured by a hand-held dynamometer and the Ashworth Scale, respectively. Functional abilities were assessed by the Gross Motor Function Measure and by calculating the energy expenditure index from data collected during two three-minute walk tests (comfortable and fast speeds). RESULTS: Significant relationships were found between impairments and functional abilities (r = 0.42-0.85, p < 0.05). Isometric hamstring strength and quadriceps spasticity explained 81.5% of total Gross Motor Function Measure score variance. Quadriceps spasticity explained 56.7% of energy expenditure index variance during comfortable walking. CONCLUSION: Hamstring strength and quadriceps spasticity explain much of the variance in gross motor function and comfortable walking efficiency.

Cerebral Palsy↗
PubMed2003

A clinically applicable EMG-force model to quantify active stabilization of the knee after a lesion of the anterior cruciate ligament.

OBJECTIVES: To investigate whether a simple electromyography-force (EMG-force) model can be used to measure different levels of co-contraction about the knee for healthy subjects and patients with an anterior cruciate ligament deficiency. DESIGN: To evaluate an EMG-to-force processing model, two groups of subjects, with and without deficiency of the anterior cruciate ligament, participated in experiments in which surface EMG, kinematics and kinetics about the knee were recorded during isokinetic and functional movements. BACKGROUND: Clinical and biomechanical evidence supports the hypothesis that higher level of co-contraction of quadriceps and hamstrings provide an active stabilization of the knee to compensate for the lost anterior cruciate ligament. To quantify the level of co-contraction, the contribution of both agonist and antagonist muscles to the net joint moment must be known. METHODS: Surface EMG levels were calibrated to moment by means of a limited number of isokinetic contractions about the knee. With these calibration values, an estimate of the muscle moments during a vertical jump were obtained and compared with the net joint moment, calculated with inverse dynamics. Also co-contraction indices were determined. RESULTS: The EMG-force model provided a fair estimate of the net joint moment. The co-contraction index in anterior cruciate ligament deficient subjects was significantly higher (mean 0.54 (SD, 0.04)) compared to healthy subjects (mean 0.25 (SD, 0.07)). CONCLUSIONS: Although the EMG-to-force processing model is not perfectly accurate, it is appropriate within a clinical context. RELEVANCE: Previous research supports the hypothesis that subjects with an anterior cruciate ligament deficiency compensate the loss of passive stability by developing higher co-activation levels of the knee muscles, i.e. active stabilization. Quantifying co-contraction may serve as a valuable parameter to evaluate clinical interventions and rehabilitation processes. The EMG-force model presented in this study appears to be a useful instrument for this purpose.

Adult↗
PubMed1995

Hemodynamics during a machine-aided flexibility protocol.

Heart rates and systolic and diastolic blood pressures of 15 subjects were measured before, during, and after a series of four proprioceptive neuromuscular facilitation (PNF) flexibility exercises. The protocol for the study involved the use of two new machines, one designed to increase flexibility of the erector spinae, the other the hamstrings. Each machine provided constant feedback of isometric force, angular displacements, time of contraction, repetitions, and other exercise variables. Each bout of exercise involved an isometric contraction of the lengthened agonist muscle group (12 sec) followed by a concentric contraction of its antagonist in order to place the body part in a more stretched position. Hemodynamic measurements were determined at both a perceived maximal voluntary isometric contraction (MVIC) and at 50% MVIC. Significant increases in hemodynamic factors were observed when exercise measures were compared to pre- and postexercise (resting) values. Higher values, though not significantly so, were found at MVIC than at 50% MVIC on both machines. All values were well within the guidelines of the American College of Sports Medicine.

Adolescent↗
PubMed1999

Electromyographic analysis and energy expenditure of harness supported treadmill walking: implications for knee rehabilitation.

Harness supported treadmill ambulation has been recommended for patients as a way of decreasing loads on the healing tissues, conserving energy and reducing pain. We quantified muscle activation levels around the knee and metabolic responses during harness supported treadmill walking. Ten healthy recreational athletes (age 28.9+/-7.8 years) walked on the treadmill (1.34 m/s) for 5 min each at full weight bearing (FWB), 20 and 40% body weight support (BWS). Electromyography (EMG) was monitored for the vastus lateralis, vastus medialis, rectus femoris, biceps femoris, medial hamstrings and the gastrocnemius. Oxygen consumption was collected by open circuit spirometry and the heart rate was collected by a heartwatch. A statistically significant reduction in EMG was found at 40% BWS for the quadriceps. Oxygen consumption decreased by 6% (20% BWS) and by 12% (40% BWS) from FWB (P<0.05). The heart rate was unchanged. BWS ambulation reduces energy cost, but does not significantly alter muscle activation, except for the quadriceps at 40% BWS.

Adult↗
PubMed1996

Thermal pants may reduce the risk of recurrent hamstring injuries in rugby players.

OBJECTIVE: To determine whether the use of thermal pants might reduce the risk of hamstring injury in rugby players. METHODS: 44 male rugby players from the Cape Province, South Africa, who had previously suffered a hamstring injury were given the choice of wearing thermal warming pants or not, and were then monitored for the development of hamstring injuries during the 1992 season. RESULTS: In the group who wore warmers some of the time, the injury rate was significantly lower when using the warmers (3 injuries/1000 playing hours) than when not (57/1000 playing hours). There was no difference in injury rates between groups who either wore warmers all the time or none of the time, probably because the number who wore the warmers all the time was small (n = 5). Eighteen percent of the injuries recurred at exactly the same site in the muscle and within 12 d of returning to rugby after the initial injury. The incidence of injury was high in the first three weeks of the season and again in the same period after the mid-season break. More than 80% of all match and practice time lost by these players during the study was a direct result of their hamstring injuries. CONCLUSIONS: Thermal pants may have a role in preventing recurrent hamstring injuries but other factors such as inadequate preseason training and incomplete rehabilitation after injury are likely to be more significant risk factors for injury.

Adult↗