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.

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recent vears, the predominant philosophv of physical therapists and athletic trainers in treating lower extremity injuries has focused on the use of closed kinetic chain exercises. This is based on both observational and experimental data that suggest such exercises are more effective, safer, and more functional than previouslv emploved open kinetic chain exercises (3,8,9,12,20,23,29,30,37,58,41). M'hile a variety of techniques are typically used to create a closed kinetic chain environment, one that has evoked particular interest is backward walking (19,24,25). The functionality of both backward and forward walking in rehabilitation is quite obvious. However, it has been suggested that backward walking mav off'er some benefits beyond those experienced through forward walking alone. Gray reported his observation that backward walking appeared to create "more muscle activity in proportion to effort" than forward walking (24). This observation is supported by research demonstrating that the energy cost of backward walking is greater than that of forward walking ( 1 ) . Both Vilenskv et al (48) and Kramer and Reid (27) concluded that backward walking was different from forward walking. Thev reported that backward walking was associated with increased cadence and decreased stride length when compared with forward walking. These authors also observed that thejoint kinematics involved in backward walking were substantially different from those of forward walking (27.48). In contrast, however, Winter and Pluck (51) concluded that backward walking was a near mirror image of forward walking. Thev reported that, in order to produce the muscle activation patterns involved in forward walking, the

The aim of the study was to investigate differences in frontal plane knee kinetics, onset timing and duration of the gluteus medius (GMed), adductor longus (AL), and vastus medialis oblique (VMO) during stair ambulation between those with and without patellofemoral pain syndrome (PFPS). Twenty PFPS patients and twenty healthy participants completed stair ambulation while surface electromyography (EMG), video, and ground reaction forces were collected. PFPS patients had a higher peak internal knee abduction moment during stair ascent, and a higher internal knee abduction impulse for both ascent and descent. During stair ascent, PFPS patients displayed earlier onset of the AL and later onset of GMed, compared to the healthy individuals. Also, PFPS patients had longer activation duration of the AL and shorter activation durations of the VMO and GMed during stair ascent. During stair descent, PFPS patients displayed delayed GMed onset and shorter activation duration of GMed and VMO. The results of the study suggest that altered neuromuscular control of the medial thigh musculature may be an important contributor to PFPS.