Effect of underwater treadmill exercise on postural sway in horses with experimentally induced carpal joint osteoarthritis.

OBJECTIVE: To evaluate the effect of underwater treadmill exercise on static postural sway in horses with experimentally induced carpal joint osteoarthritis under various stance conditions. ANIMALS: 16 horses. PROCEDURES: On day 0, osteoarthritis was induced arthroscopically in 1 randomly selected middle carpal joint of each horse. Beginning on day 15, horses were assigned to either underwater or overground (without water) treadmill exercise at the same speed, frequency, and duration. Two serial force platforms were used to collect postural sway data from each horse on study days -7, 14, 42, and 70. Horses were made to stand stationary on the force platforms under 3 stance conditions: normal square stance, base-narrow placement of the thoracic limbs, and removal of visual cues (blindfolded) during a normal square stance. The mean of 3 consecutive, 10-second trials in each condition was calculated and used for analysis. RESULTS: Displacement of the center of pressure differed significantly depending on the stance condition. Among horses exercised on the underwater treadmill, postural stability in both the base-narrow and blindfolded stance conditions improved, compared with findings for horses exercised on the overground treadmill. Horses exercised on the overground treadmill were only successful at maintaining a stable center of pressure during the normal square stance position. CONCLUSIONS AND CLINICAL RELEVANCE: Variations in stance position had profound effects on the mechanics of standing balance in horses with experimentally induced carpal joint osteoarthritis. Underwater treadmill exercise significantly improved the horses' postural stability, which is fundamental in providing evidence-based support for equine aquatic exercise.

Interactive variable resistance exercise system concept and preliminary results.

In order to maximize loading during resistance exercise, muscles should be heavily taxed throughout the entire range of motion for that exercise. Traditional constant resistance squats only tax the lower-extremity muscles to their limits at the "sticking region" or a critical joint configuration of the exercise cycle. Therefore, a Smith machine was modified for pneumatic resistance with appropriate computer control so that it is capable of adjusting force within a repetition of the squat exercise. The control program was designed to increase the loading after accelerating to a specified lifting velocity which indicates increased strength capacity from being past the sticking region. Human subject testing showed the percent increase from initial to final resistance level normalized by body and barbell weight was an average of 14% (+/-5%) for men and 29% (+/-14%) for women with both separately showing a significant increase in resistance level (p>0.00005 each). The men had significantly higher initial (p=0.007) and final (p=0.04) normalized resistance levels than the women. This investigation indicates that interactive variable resistance exercise is capable of significantly increasing the loading after a desired instantaneous velocity is reached; however, further performance testing is required to determine its efficacy.

Trial number and duration effects on standing weightbearing asymmetry measures.

Side-to-side weight-bearing asymmetries during quiet bilateral stance may be important in the study of postural control and low back pain. However, clear and appropriate methods to measure and categorize these asymmetries have not been determined. The goal of this investigation was to evaluate trial number and duration when using a statistical means for categorization. Eleven healthy subjects completed ten trials of 20 second quiet stance while standing naturally with feet at shoulder width on two force platforms. The average of the first 5 seconds of vertical ground reaction force was compared with that of the entire 20 seconds. Subjects repeated the procedure within ten days. Symmetry/asymmetry categorization was determined by conducting repeated measures t-tests (p > 0.01) on the percent of body weight placed on the right foot compared to the left. Intra-class correlation coefficients (ICCr) were utilized to assess trial duration and day-to-day variations. Statistical power was used to evaluate the adequacy of ten trials. Statistical categorization was identical when using 5 and 20 seconds of data, except for two subjects that were found to be asymmetric over 5 seconds and symmetric over 20 seconds on the second day (ICCr = 0.995 day 1, 0.993 day 2). Power estimates indicated that one more trial would be necessary to categorize those with p values approaching significance (p > = 0.040) as asymmetric while 20 or more trials would be needed for others (p >= 0.117). Day-to-day repeatability was high (ICCr = 0.924 for 5 seconds, 0.927 for 20 seconds) with only two subjects changing from an asymmetric categorization on the first day to symmetric on the second day (20 seconds duration only). In conclusion, short duration trials (~5 seconds) may be adequate for use when evaluating weight-bearing asymmetries. However, due to the relatively large number of trials needed for this statistical method, other options should be pursued (which might reduce the number of trials but increase the duration of the trial). Finally, weight-bearing asymmetries are highly consistent from day-to-day, indicating measures taken on a single day should be representative of typical musculoskeletal loading during quiet stance.