Flexural wave propagation velocity and bone mineral density in females with and without tibial bone stress injuries.

STUDY DESIGN: Case-control nonexperimental design. OBJECTIVES: To compare flexural wave propagation velocity (FWPV) and tibial bone mineral density (BMD) in women with and without tibial bone stress injuries (BSIs). BACKGROUND: Physical therapists, particularly in military and sports medicine settings, routinely diagnose and manage stress fractures or bone stress injuries. Improved methods of preparticipation quantification of tibial strength may provide markers of BSI risk and thus potentially reduce morbidity. METHODS AND MEASURES: Bone mineral density, FWPV, bone geometry, and historical variables were collected from 14 subjects diagnosed with tibial BSIs and 14 age-matched controls; all 28 were undergoing military training. RESULTS: No difference was found between groups in FWPV and tibial BMD when analyzed with t tests (post hoc power = 0.89 and 0.81, respectively). Furthermore, no difference was found in tibial length, tibial width, femoral neck BMD, and lumbar spine BMD among the groups. There were no differences between the 2 groups in smoking history, birth control pill use, and onset of menarche. Finally, sensitivity and positive likelihood ratios for FWPV (0.14 and 0.63), tibial BMD (0.0 and 0.0), and lumbar BMD (0.18 and 2.0) were low, while specificity was high (0.77, 0.93, and 0.91, respectively). CONCLUSION: Current bone analysis devices and methods may not be sensitive enough to detect differences in tibial material and structure; local stresses on bone may be more important in the development of BSIs than the overall structural stiffness.

Plantar pressure reduction in an incremental weight-bearing system.

BACKGROUND AND PURPOSE: Harness-supported treadmill ambulation has been advocated for patients to provide reduction in weight bearing to healing tissues and to reduce the energy cost of treadmill ambulation. The purposes of this technical report are to analyze the ability of one of these devices (Zuni Exercise System) to support a specific percentage of a subject's body weight during walking and running and to explore the relationship of unloading to pressure reduction in selected plantar surface regions of the foot. SUBJECTS: Ten male volunteers with no known foot pathology participated. METHODS: In-shoe plantar pressure and vertical ground reaction forces (GRFs) were measured during walking and running at full body weight and at 20% of body weight supported. RESULTS: Walking at a setting of 20% of body weight supported resulted in a reduction of the first and second vertical force peaks of 23.8% (SD = 7.3%) and 27.2% (SD = 4.1%), respectively. The total force-time integral during walking unloaded was 22.8% (SD = 3.3%). During running, the active vertical force peak and total force-time integral were reduced by 19.9% (SD = 6.0%) and 20.0% (SD = 3.3%), respectively, in the unloaded condition. Plantar pressures were reduced from 6.8% to 27.8% in the body weight-supported conditions. The reduction was variable across different regions of the foot. CONCLUSION AND DISCUSSION: The Zuni Exercise System appears to reduce the vertical component of the GRF during walking and running with 20% of body weight supported. Plantar pressures were reduced during body weight-supported conditions, but the reduction varied at different regions of the foot.

Patellofemoral joint compressive forces in forward and backward running.

The use of backward running is becoming more common in the rehabilitation setting. In particular, backward running has been suggested as a treatment modality in patients experiencing patellofemoral pain syndrome. To date, no study has examined the loads at the patellofemoral joint during backward running. The purpose of this study was to compare patellofemoral joint compressive forces during forward and backward running. Ground reaction force and kinematic data were collected on five male joggers during free speed forward and backward running. A floor reaction force vector model was used to calculate the stance phase knee extension moments. The distance used for the extensor muscle lever arm was 4.9 cm. Patellar mechanism angle was calculated based on knee joint angle. There was a reduction in the peak patellofemoral joint compressive forces in backward compared with forward running (2277 +/- 192N vs. 4253 +/- 1292N; p < 0.05) at self-selected speeds. Peak patellofemoral joint compressive force occurred significantly later (p < 0.05) in the stance phase of backward running (52 +/- 4%) than in forward running (35 +/- 3%). The peak patellofemoral joint compressive force normalized to subject body weight was 5.6 +/- 1.3 body weight in forward running and 3.0 +/- 0.6 body weight in backward running. The results suggest that backward running at a self-selected speed may reduce patellofemoral joint compressive forces and, coupled with the quadriceps strengthening that has previously been reported, may be beneficial in the rehabilitation of patellofemoral pain syndrome in runners. However, constant speed comparisons or other models may yield different results.

Comparison of cardiopulmonary responses to forward and backward walking and running.

Backward running has long been used in sports conditioning programs and has recently been incorporated into rehabilitative settings as a method of increasing quadriceps strength while decreasing the joint compressive forces about the knee. Although backward locomotion has been studied kinetically, the metabolic cost of backward walking and/or running has not to our knowledge been previously characterized. Oxygen consumption and other cardiopulmonary variables were measured under constant speed exercise during backward and forward walking at 107.2 m.min-1 and during backward and forward running at 160.8 m.min-1. Peak oxygen consumption (VO2peak) was also measured during maximal incremental backward and forward running. VO2, HR, and blood lactate were significantly higher (P < 0.001) during backward walking and running than during forward walking and running. During backward walking and backward running, subjects exercised at 60% and 84% of their forward VO2peak, respectively. In conclusion, for a given speed, backward locomotion elicits a greater metabolic demand and cardiopulmonary response than forward locomotion. In general, these data suggest that while undergoing rehabilitation, an injured athlete may continue to exercise using backward walking/running at an intensity sufficient enough to maintain cardiovascular fitness levels.

Mechanical power and muscle action during forward and backward running.

Recently, there has been increasing interest in using backward running (BR) as an exercise and rehabilitation tool. To date, no study has been performed that combined electromyography (EMG) and joint kinetics to study BR. The purpose of this study was to compare selected EMG and kinetic parameters in the stance phase of forward running (FR) and backward running (BR). The sagittal plane of the right knee was analyzed during three trials of FR and BR in six male subjects. Four 60-Hz video cameras collected motion data, and a link segment model of the right lower extremity was established. Force plate and EMG data were collected at 1000 Hz and synchronized with the video data. The knee muscle peak (+) and peak (-) mechanical power and total (+) and total (-) mechanical work were calculated. Electromyography signals were captured from the right lower extremity on the rectus femoris, vastus lateralis, vastus medialis, biceps femoris, gastrocnemius, and tibialis anterior muscles. Statistical analysis indicated that significantly less (p < 0.05) peak (+) and (-) power and total (+) work occurred at the knee during BR than during FR. Significant differences (p < .05) in muscle firing patterns between conditions were observed. Muscle action of the vastus lateralis (VL) and vastus medialis oblique (VMO) was largely eccentric and concentric during FR and isometric and concentric during BR. Backward running appears to be a good method for achieving isometric and concentric muscle action of the VMO and VL and may be useful in clinical conditions that require an increase in knee extensor strength.