Dynamic balance is required for normal daily activities, such as walking, running, and stair climbing. Sports activities also require proper balance control. The visual, somatosensory, and vestibular systems all contribute to the maintenance of balance (10) and may be adversely affected by musculoskeletal injury, head trauma, disease, or aging. These influences on the visual, somatosensory, and vestibular systems might decrease a person's ability to perform dynamic activities and, thus, impede normal daily functioning (2,6,17,23). Quantification of balance, or postural control, is often necessary to assess the level of injury or ability to function in order to initiate an appropriate plan of care (15,17).A valid and reliable technique to measure balance is stabilometry (1 7). This method uses a force plate or other similar device to measure the displacement of an individual's center-of-pressure while standing in a stationary position (1 7). Center-ofpressure represents a weighted average of all the pressures over the surface area in contact with the ground (20). Quan tification of center-of-pressure movement may be used to evaluate numerous parameters (ie., mean position of the center-of-pressure, velocity of center-of-pressure movement, and total distance traveled by the center-of-pressure) influenced by the control mechanism affecting balance (16).Many activities of daily living and sports are classified as dynamic activi-

The purpose of this study was to determine the relationship between hip and knee strength, and valgus knee motion during a single leg squat. Thirty healthy adults (15 men, 15 women) stood on their preferred foot, squatted to approximately 60 deg of knee flexion, and returned to the standing position. Frontal plane knee motion was evaluated using 3-D motion analysis. During Session 2, isokinetic (60 deg/sec) concentric and eccentric hip (abduction/adduction, flexion/extension, and internal/external rotation) and knee (flexion/extension) strength was evaluated. The results demonstrated that hip abduction (r2=0.13), knee flexion (r2=0.18), and knee extension (r2=0.14) peak torque were significant predictors of frontal plane knee motion. Significant negative correlations showed that individuals with greater hip abduction (r=-0.37), knee flexion (r=-0.43), and knee extension (r=-0.37) peak torque exhibited less motion toward the valgus direction. Men exhibited significantly greater absolute peak torque for all motions, excluding eccentric internal rotation. When normalized to body mass, men demonstrated significantly greater strength than women for concentric hip adduction and flexion, knee flexion and extension, and eccentric hip extension. The major findings demonstrate a significant role of hip muscle strength in the control of frontal plane knee motion.

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Women aged 67-84 yr were randomly assigned to either resistance exercise (RE, n = 15) or control group (C, n = 14). RE group completed 10 wk of resistance training, whereas C group maintained normal activity. Blood samples were obtained from the RE group (at the same time points as for resting C) at rest, immediately after resistance exercise, and 2 h after exercise before (week 0) and after (week 10) training. Mononuclear cell (CD3+, CD3+CD4+, CD3+CD8+, CD19+, and CD3-CD16+CD56+) number, lymphocyte proliferative (LP) response to mitogen, natural cell-mediated cytotoxicity (NCMC), and serum cortisol levels were determined. Strength increased significantly in RE subjects (%change 8-repetition maximum = 148%). No significant group, exercise time, or training effects were found for CD3+, CD3+CD4+, or CD3+CD8+ cells, but there was a significant exercise time effect for CD3-CD16+CD56+ cells. LP response was not different between groups, across exercise time, or after training. NCMC was increased immediately after exercise for RE subjects at week 0 and for RE and C groups at week 10. The week 0 and week 10 NCMC values were above baseline for both RE and C groups 2 h after exercise. In conclusion, acute resistance exercise did not result in postexercise suppression of NCMC or LP, and 10 wk of resistance training did not influence resting immune measures in women aged 67-84 yr.