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Biomedical subjects

C M Powers

Publications and source records attributed to C M Powers.

At least 19 recordsLinked to original sources
PubMed2006

Prediction of slips: an evaluation of utilized coefficient of friction and available slip resistance.

The purpose of this study was to investigate the relationship between measures of floor surface slip resistance and an individual's peak utilized coefficient of friction (COFU) on the probability of a slip occurring during level walking. Video, kinematic and ground reaction force data were recorded simultaneously as subjects walked at a self-selected speed during conditions of normal and reduced floor surface slip resistance. Peak COFU during weight acceptance was calculated and the available floor surface slip resistance was measured using the variable incidence tribometer (VIT). Separate logistic regression analyses identified that knowledge of the available slip resistance (as measured by the VIT) in combination with an individual's peak COFU allowed for greater accuracy in classifying slip outcomes (89.5%; p = 0.004), while knowledge of only the available slip resistance reduced the accuracy of categorization to 78.9% (p = 0.021).

Accidental Falls↗
PubMed2001

Patellofemoral joint kinetics during squatting in collegiate women athletes.

OBJECTIVE: To characterize the biomechanics of the patellofemoral joint during squatting in collegiate women athletes. DESIGN: Repeated measures experimental design. BACKGROUND: Although squatting exercises are required components of most intercollegiate resistance-training programs and are commonly performed during rehabilitation, the effects of various squatting depths on patellofemoral joint stress have not been quantified. METHODS: Anthropometric data, three-dimensional knee kinematics, and ground reaction forces were used to calculate the knee extensor moment (inverse dynamics approach) in five intercollegiate female athletes during squatting exercise at three different depths (approximately 70 degrees, 90 degrees and 110 degrees of knee flexion). A biomechanical model of the patellofemoral joint was used to quantify the patellofemoral joint reaction force and patellofemoral joint stress during each trial. RESULTS: Peak knee extensor moment, patellofemoral joint reaction force and patellofemoral joint stress did not vary significantly between the three squatting trials. CONCLUSIONS: Squatting from 70 degrees to 110 degrees of knee flexion had little effect on patellofemoral joint kinetics. The relative constancy of the patellofemoral joint reaction force and joint stress appeared to be related to a consistent knee extensor moment produced across the three squatting depths. RELEVANCE: The results of this study do not support the premise that squatting to 110 degrees places greater stress on the patellofemoral joint than squatting to 70 degrees. These findings may have implications with respect to the safe design of athletic training regimens and rehabilitation programs.

Adult↗
PubMed2001

Lower extremity kinetics during stair ambulation in patients with and without patellofemoral pain.

OBJECTIVE: To compare lower extremity kinetics during stair ascent and descent in subjects with and without patellofemoral pain. DESIGN: A cross-sectional study utilizing a control group. BACKGROUND: The patellofemoral joint reaction force (the resultant force between the quadriceps muscle force and patellar ligament force) increases with quadriceps force and knee flexion angle. Consequently, patients with patellofemoral pain may employ compensatory strategies to minimize pain and reduce patellofemoral joint reaction forces during activity. METHODS: 10 individuals with a diagnosis of patellofemoral pain and 10 individuals without pain participated. Subject groups were matched on sex, age, height, and body mass. Anthropometric data, three dimensional kinematics, and ground reaction forces were used to calculate lower extremity sagittal plane moments (inverse dynamics) while subjects ascended and descended stairs at a self-selected pace. Differences in kinetic variables between groups were assessed using 2x2 (group x stair condition) analysis of variance. RESULTS: Subjects with patellofemoral pain had decreased peak knee extensor moments during stair ascent and descent. There were no group differences in peak hip, ankle, or support moments, however, subjects with patellofemoral pain had decreased cadence (descent) compared to controls. CONCLUSION: Subjects with patellofemoral pain had reduced peak knee extensor moments, suggesting that quadriceps avoidance was employed to reduce patellofemoral joint reaction forces. The lack of group differences in peak moments at the hip and ankle suggests that secondary compensation did not occur exclusively at the hip or ankle in this group of subjects with patellofemoral pain. RELEVANCE STATEMENT: Because stair ambulation is often used to evaluate the reproducibility of symptoms and to identify abnormal movement patterns indicative of patellofemoral pain, knowledge of lower extremity mechanics during stair negotiation is necessary to better characterize compensatory behavior in this population.

Adult↗
PubMed2001

Electromyographic activity of selected trunk muscles during dynamic spine stabilization exercises.

OBJECTIVES: To compare the electromyographic activity of the trunk flexors and extensors during 2 spine stabilization exercises and to evaluate the changes in muscle activity with increasing levels of exercise difficulty. DESIGN: Descriptive study. SETTING: Research laboratory. PARTICIPANTS: Twelve healthy subjects without history of lower back pain. INTERVENTION: Subjects were instructed how to perform the Dying Bug and the Quadruped exercises. Electromyographic and motion data were recorded from each muscle group during maximum voluntary isometric contraction (MVIC). MAIN OUTCOME MEASURES: Surface electromyographic recordings of the erector spinae, rectus abdominus, abdominal oblique, and gluteus maximus muscles. RESULTS: During the Dying Bug exercise, the trunk flexors (rectus abdominus, abdominal oblique) were equally active and demonstrated proportional increases in electromyographic activity with increasing level of exercise difficulty. In the Quadruped exercise, significantly greater electromyographic activity was observed in the abdominal oblique compared with the rectus abdominus; however, abdominal oblique activity did not change with increasing level of difficulty. The erector spinae and gluteus maximus demonstrated a significant level effect and were most active during elevation of the ipsilateral leg. At no point did activity of any of the muscles studied exceed 41% of the MVIC. CONCLUSIONS: Results indicated the Dying Bug exercise predominantly recruited the abdominal musculature, while greater activity was observed in the trunk and hip extensors during the Quadruped exercise. The relatively low levels of electromyographic activity observed in both exercises suggests that the intensity of muscle recruitment is not likely sufficient to provide a strengthening effect in healthy subjects.

Abdominal Muscles↗
PubMed2001

The effects of eccentric velocity on activation of elbow flexors: evaluation by magnetic resonance imaging.

PURPOSE: To compare magnetic resonance imaging (MRI) signal intensity changes in the primary elbow flexors during two isotonic exercise protocols varying in eccentric velocity and the ratio of eccentric to concentric activity. METHODS: Twelve men performed two exercise protocols. The right and left arms were randomly assigned to one of two protocols that had the same workload (60% 1RM) and same total time of exercise (144 s) but differed in the velocity and ratio of eccentric to concentric activity (1:1 and 5:1 for the fast and slow protocols, respectively). MRI signal intensity changes were quantified pre- and post-exercises using an inversion recovery sequence with a 1.5T MRI system (TR = 2500 ms, TE = 90 ms, TI = 140 ms). Percent change in MRI signal intensity, rate of perceived exertion (RPE), and delayed onset muscle soreness (DOMS) were recorded and analyzed. RESULTS: The biceps brachii was found to be preferentially recruited during the fast protocol compared with the brachialis, whereas the brachialis was found to be preferentially recruited during the slow protocol (P < 0.05). The fast exercise protocol was perceived as being more strenuous (RPE = 8.3 +/- 2.1) than the slow (RPE = 5.4 +/- 1.5, P < 0.05) and produced DOMS in 58% of the tested subjects. CONCLUSIONS: These results suggest that agonists respond to various loading conditions nonhomogeneously. These findings may have implications with respect to exercise prescriptions for specific muscles.

Adult↗
PubMed2000

The influence of lower extremity joint torque on gait characteristics in elderly men.

OBJECTIVE: To examine the relation between certain lower extremity isokinetic muscle torque capabilities and selected stride characteristics for a group of elderly, sedentary men. STUDY DESIGN: Descriptive analysis of convenience sample. SETTING: Veterans Administration (VA) ambulatory care center. SUBJECTS: Eighty-one elderly men, capable of independent ambulation, were recruited from outpatient clinics and the local community (mean age, 74.7yr). MAIN OUTCOME MEASURES: Maximal isokinetic torque in the sagittal plane of hip, knee, and ankle muscles; stride characteristics of speed, stride length, and cadence recorded during walking at a self-selected velocity. RESULTS: Stepwise regression analysis revealed that hip extension torque was the only significant independent predictor for free walking speed, stride length, and cadence, and accounted for 37% (r = .611), 35% (r = .590), and 12% (r = .341) of the total variance, respectively. Other joint torques correlated with gait parameters but did not add significantly to the multivariate model. CONCLUSIONS: Hip extension torque was the only significant independent predictor for free walking velocity, stride length, and cadence in this group. These results support the idea that strengthening the hip extensors may improve stride characteristics in elderly individuals.

Aged↗
PubMed2000

Patellar kinematics, part I: the influence of vastus muscle activity in subjects with and without patellofemoral pain.

BACKGROUND AND PURPOSE: Reduced motor unit activity of the vastus medialis muscle relative to the vastus lateralis muscle has been implicated as a cause of lateral patellar subluxation. The purpose of this study was to assess the influence of vastus muscle motor unit activity on patellar kinematics. SUBJECTS: Twenty-three women (mean age=26.8 years, SD=8.5, range=14-46) with a diagnosis of patellofemoral pain and 12 women (mean age=29.1 years, SD=5.0, range=24-38) without patellofemoral pain participated. Only female subjects were studied because of potential biomechanical differences between sexes. METHODS: Patellar kinematics (kinematic magnetic resonance imaging) and vastus muscle electromyographic (EMG) activity using indwelling electrodes were measured during resisted knee extension. Measurements of medial and lateral patellar displacement and tilt obtained from magnetic resonance images were correlated with normalized vastus lateralis:vastus medialis oblique muscle and vastus lateralis:vastus medialis longus muscle EMG ratios at 45, 36, 27, 18, 9, and 0 degrees of knee flexion using a stepwise regression procedure. RESULTS: The vastus lateralis:vastus medialis longus muscle EMG ratio contributed to the prediction of lateral patellar glide at 27 degrees of knee flexion (r=-.48), with increased vastus medialis longus muscle activity being associated with greater lateral patellar displacement. A similar inverse relationship was evident with lateral patellar tilt at 36, 27, 18, and 9 degrees of knee flexion. CONCLUSION AND DISCUSSION: These results suggest that increased motor unit activity of the vastus medialis muscle appears to be associated with abnormal patellar kinematics in women, but it is not necessarily a cause of abnormal patellar kinematics.

Adolescent↗
PubMed2000

Patellar kinematics, part II: the influence of the depth of the trochlear groove in subjects with and without patellofemoral pain.

BACKGROUND AND PURPOSE: A shallow intercondylar groove has been implicated as being contributory to abnormal patellar alignment. The purpose of this study was to assess the influence of the depth of the intercondylar groove on patellar kinematics. SUBJECTS: Twenty-three women (mean age=26.8 years, SD=8.5, range=14-46) with a diagnosis of patellofemoral pain and 12 women (mean age=29.1 years, SD=5.0, range=24-38) without patellofemoral pain participated. Only female subjects were studied because of potential biomechanical differences between sexes. METHODS: Patellar kinematics were assessed during resisted knee extension using kinematic magnetic resonance imaging. Measurements of medial and lateral patellar displacement and tilt were correlated with the depth of the trochlear groove (sulcus angle) at 45, 36, 27, 18, 9, and 0 degrees of knee flexion using regression analysis. RESULTS: The depth of the trochlear groove was found to be correlated with patellar kinematics, with increased shallowness being predictive of lateral patellar tilt at 27, 18, 9, and 0 degrees of flexion and of lateral patellar displacement at 9 and 0 degrees of flexion (r=.51-.76). CONCLUSION AND DISCUSSION: The results of this study indicate that bony structure is an important determinant of patellar kinematics at end-range knee extension (0(-30().

Adolescent↗
PubMed1999

The influence of patellofemoral pain on lower limb loading during gait.

OBJECTIVE: To determine if subjects with patellofemoral pain demonstrate excessive lower limb loading during gait. DESIGN: Prospective study utilizing a group of patients with patellofemoral pain and a control group. BACKGROUND: Increased rate of lower limb loading has been hypothesized as being contributory to knee osteoarthritis and may be the result of decreased knee flexion during weight acceptance. Since patients with patellofemoral pain have been reported to limit knee flexion during gait, these individuals may be at risk for the adverse effects of impulse loading. METHODS: Force plate parameters, lower extremity kinematics and stride characteristics were recorded in 15 females with patellofemoral pain and 10 pain-free controls during self-selected free and fast walking velocities. RESULTS: Individuals in the patellofemoral pain group demonstrated a significantly slower gait velocity during the free and fast trials as well as decreased stance phase knee flexion during fast walking. The average peak loading rate for the patellofemoral pain group was significantly less than the control group during both free (P=0.004) and fast walking (P=0. 03). CONCLUSIONS: Despite diminished stance phase knee flexion during fast walking, subjects with patellofemoral pain did not demonstrate increased lower limb loading. During gait, the ground reaction forces appeared to be minimized by adopting a slower walking velocity. RELEVANCE: These results indicate that altered knee kinematics as a result of patellofemoral pain do not place these individuals at risk for the adverse effects of impulse loading.

Adolescent↗
PubMed1999

Effect of bracing on patellar kinematics in patients with patellofemoral joint pain.

PURPOSE: Bracing is commonly used to correct patellar malalignment syndromes. However, there are little objective data documenting the effect of such supports on patellofemoral joint relationships. The purpose of this study was to assess the effectiveness of an elastic patellofemoral sleeve brace in altering patellar tracking in subjects with patellofemoral pain. METHODS: Ten female subjects (12 patellofemoral joints) between the ages of 17 and 46 participated in this study. All subjects had a diagnosis of patellofemoral pain and demonstrated lateral patellar tracking based on magnetic resonance imaging (MRI) assessment. Each subject underwent kinematic MRI of the patellofemoral joint through a range of 45 to 0 degrees of knee flexion against a resistance of 15% body weight. Imaging was performed with and without a patellofemoral joint brace (Bauerfeind Genutrain P3 brace, Atlanta, GA). Measurement of medial/lateral patellar displacement, medial/lateral patellar tilt, and the depth of the trochlear groove (sulcus angle) were obtained with midpatellar image sections at 45, 36, 27, 18, 9 and 0 degrees of knee flexion. RESULTS: No statistically significant differences in medial/lateral patellar displacement or tilt were found between braced and unbraced trials across all knee flexion angles (P < 0.05). A small but statistically significant increase in sulcus angle was found across all knee flexion angles with the braced trials (P > 0.05). CONCLUSIONS: These results do not support the hypothesis that the brace used in this study corrects patellar tracking patterns in subjects with patellofemoral pain. However, the increased sulcus angle indicates a change in patella position within the trochlea. It is possible that the clinical improvements seen with bracing may be the result of subtle differences in joint mechanics and not gross changes in alignment.

Adolescent↗
PubMed1999

Relationship between foot pronation and rotation of the tibia and femur during walking.

The purpose of this study was to test the hypothesis that the magnitude and timing of peak foot pronation would be predictive of the magnitude and timing of peak rotation of tibia and femur. Thirty subjects who demonstrated a wide range of pronation participated. Three-dimensional kinematics of the foot, tibia, and femur segments were recorded during self-selected free walking trials using a six-camera VICON motion analysis system. Regression analysis demonstrated that the magnitude and timing of peak pronation was not predictive of the magnitude and timing of tibial and femoral rotation. The lack of a relationship between peak foot pronation and the rotation of the tibia and femur is contrary to the clinical hypothesis that increased pronation results in greater lower extremity rotation. It would seem, therefore, that the relationship between foot pronation and rotation of the lower extremity segments should be assessed on a patient-by-patient basis.

Adult↗
PubMed1999

Criterion-related validity of a clinical measurement to determine the medial/lateral component of patellar orientation.

STUDY DESIGN: Repeated measures design using a sample of convenience. OBJECTIVE: To assess the criterion-related validity and intrarater reliability of a clinical measurement used for determining the medial/lateral position of the patella. BACKGROUND: Patellar taping is a common treatment for patellofemoral pain. Application of this intervention requires accurate assessment of patellar orientation; however, the validity of this clinical procedure has not been documented. METHODS AND MEASURES: Fourteen subjects (10 women, 4 men; average age, 41 +/- 16 years) were evaluated. Clinical assessment of medial/lateral patellar orientation using the technique described by McConnell was compared with the actual position of the patella as determined through magnetic resonance imaging (MRI). Imaging was done on 7 knees of 4 subjects who were asymptomatic and 11 knees of 10 subjects who were symptomatic. Both clinical and MRI assessments were made with the subjects supine, the knee extended, and the quadriceps relaxed. Agreement between the 2 techniques and the intrarater reliability of each measurement were quantified by means of the intraclass correlation coefficient (ICC). RESULTS: Both the clinical and MRI measures of medial/lateral patellar displacement were found to demonstrate good intrarater reliability (ICC = 0.91 and 0.85, respectively). The agreement between the clinical and MRI determinations of medial/lateral patellar position was poor (ICC = 0.44). The average amount of lateral patellar displacement as determined by the clinical method was more than twice that established through MRI. CONCLUSIONS: The clinical assessment of the medial/lateral position of the patella overestimates the true amount of lateral patellar displacement. A more valid clinical method of assessing the medial/lateral component of patellar orientation is necessary.

Adult↗
PubMed1998

Effects of distal cement voids on cement stress in total hip arthroplasty.

The purpose of this study was to determine whether voids in the distal cement mantle created during total hip arthroplasty increase cement stress at the distal tip of the femoral component. Using a three-dimensional finite element model of an idealized, cylindrical femoral shaft with implanted prosthesis, peak von Mises stress in the cement mantle was evaluated for five different air-bubble configurations and two cement mantle thicknesses, 2 mm and 5 mm. Results indicated that voids in the cement mantle increased peak cement stress at the medial tip of the prosthesis by 2% to 57%, with greater increases in stress being evident with larger bubble sizes. On the average, peak stresses were 53% greater in the models with the thinner cement mantle. Clinicians are encouraged to use a thicker cement mantle and to avoid bubble formation during total hip arthroplasty.

Arthroplasty, Replacement, Knee↗
PubMed1998

Rehabilitation of patellofemoral joint disorders: a critical review.

Patellofemoral pain is one of the most common knee disorders seen in orthopaedic practice. Despite its high incidence, treatment of this disorder remains controversial. Traditionally, nonoperative management of patellofemoral pain has focused on restoring normal patellar tracking by improving dynamic stability. Of particular interest to clinicians has been the vastus medialis oblique, which has been implicated as being the primary medial stabilizer of the patella. Although emphasis on the vastus medialis oblique continues to be the mainstay of conservative care of patellofemoral pain, there exists considerable disagreement between research outcomes and clinical practice. This article critically reviews the current literature concerning the treatment of patellofemoral pain with respect to the vastus medialis oblique, taping, and bracing, as well as various forms of therapeutic exercise, and relates these findings to the prevailing views regarding the management of this disorder.

Biomechanical Phenomena↗
PubMed1997

Are patellofemoral pain and quadriceps femoris muscle torque associated with locomotor function?

BACKGROUND AND PURPOSE: The purpose of this investigation was to determine the influence of pain and muscle weakness on gait variables in subjects with patellofemoral pain (PFP). SUBJECTS: Nineteen female subjects with a diagnosis of PFP and 19 female subjects without PFP participated in the study. METHODS: Subjects underwent gait analysis (stride characteristics and joint motion) during level walking, ascending and descending stairs, and ascending and descending ramps, in addition to isometric torque testing of the knee extensors of the involved limb. Pain and functional status also were assessed. RESULTS: Compared with the comparison group, the primary gait compensation in the PFP group was a reduced walking speed, which was a function of both a reduced stride length and cadence. Knee extensor torque was the only predictor of gait function, with increased torque correlating with improved stride characteristics. In addition, PFP was not associated with locomotor function. CONCLUSION AND DISCUSSION: These findings suggest that functional ability in persons with PFP is associated with increased quadriceps femoris muscle torque. Future research is needed to determine whether function improves with quadriceps femoris muscle strengthening.

Adolescent↗
PubMed1997

The effects of patellar taping on stride characteristics and joint motion in subjects with patellofemoral pain.

Although patellar taping has been reported to be effective in reducing pain, the effects of this procedure on functional outcomes, such as ambulation, have not been documented. The purpose of this study was to compare stride characteristics and joint motion in subjects with patellofemoral pain, with and without the application of patellar taping using the McConnell technique. Fifteen female subjects between the ages of 14 and 41 years with diagnosis of patellofemoral pain participated in this study. Stride characteristics (Stride Analyzer) and sagittal plane joint motion (VICON) were recorded simultaneously during taped and untaped trials of free walking, fast walking, and ascending and descending a ramp and stairs. A repeated measures analysis of variance was used to determine differences between taped and untaped trials. Although subjects reported an average pain reduction of 78% using a visual analogue scale, the only significant change in stride characteristics was an increase in stride length during ramp ascent. Patellar taping did, however, result in a small but significant increase in loading response knee flexion across all conditions tested. We believe this finding demonstrates more willingness by the patellofemoral pain subjects to load the knee joint, thus permitting increased shock absorption, increased quadriceps activity, and tolerance of increased patellofemoral joint reaction force.

Adolescent↗