Jefferson W. Streepey

The role of task difficulty in the control of dynamic balance in children and adults.

Although several studies have explored the development of balance control in children, few have addressed the influence of task difficulty on balance control under dynamic and ecologically valid conditions. In this study, reaching tasks in three directions to two distances enabled the examination of balance control in the context of graded task difficulty. Balance control was measured in younger (6 years) and older (10-11 years) children and adults using center of pressure (COP) measures (initial position, excursion, and amplitude) and reach distance. Measures of the initial position of the COP and the excursion of the COP revealed no age-related differences in balance control. Furthermore, balance control, measured by the amplitude of COP movement over the course of the reaching tasks, indicated no differences between the age groups for the least difficult and most difficult tasks. For tasks of moderate difficulty, however, older children displayed levels of balance control similar to younger children for some tasks and higher levels of balance control, similar to adults, for others. This study suggests that (1) process-based measures of balance control are more sensitive in detecting age-related differences, and (2) balance control depends upon both age and the difficulty of the task being performed.

Pairing virtual reality with dynamic posturography serves to differentiate between patients experiencing visual vertigo.

BackgroundTo determine if increased visual dependence can be quantified through its impact on automatic postural responses, we have measured the combined effect on the latencies and magnitudes of postural response kinematics of transient optic flow in the pitch plane with platform rotations and translations.MethodsSix healthy (29–31 yrs) and 4 visually sensitive (27–57 yrs) subjects stood on a platform rotated (6 deg of dorsiflexion at 30 deg/sec) or translated (5 cm at 5 deg/sec) for 200 msec. Subjects either had eyes closed or viewed an immersive, stereo, wide field of view virtual environment (scene) moved in upward pitch for a 200 msec period for three 30 sec trials at 5 velocities. RMS values and peak velocities of head, trunk, and head with respect to trunk were calculated. EMG responses of 6 trunk and lower limb muscles were collected and latencies and magnitudes of responses determined.ResultsNo effect of visual velocity was observed in EMG response latencies and magnitudes. Healthy subjects exhibited significant effects (p < 0.05) of visual field velocity on peak angular velocities of the head. Head and trunk velocities and RMS values of visually sensitive subjects were significantly larger than healthy subjects (p < 0.05), but their responses were not modulated by visual field velocity. When examined individually, patients with no history of vestibular disorder demonstrated exceedingly large head velocities; patients with a history of vestibular disorder exhibited head velocities that fell within the bandwidth of healthy subjects.ConclusionDifferentiation of postural kinematics in visually sensitive subjects when exposed to the combined perturbations suggests that virtual reality technology could be useful for differential diagnosis and specifically designed interventions for individuals whose chief complaint is sensitivity to visual motion.

Effects of Quadriceps and Hamstrings Proprioceptive Neuromuscular Facilitation Stretching on Knee Movement Sensation

Streepey, JW, Mock, MJ, Riskowski, JL, VanWye, WR, Vitvitskiy, BM, and Mikesky, AE. Effects of quadriceps and hamstrings proprioceptive neuromuscular facilitation stretching on knee movement sensation. J Strength Cond Res 24(4): 1037-1042, 2010-Stretching before competition has traditionally been thought to benefit performance; however, recent evidence demonstrating reduced muscle force and power immediately after stretching suggests otherwise. We hypothesized that knee joint position sense would be diminished immediately after proprioceptive neuromuscular facilitation (PNF) stretching to the hamstrings and quadriceps. Eighteen subjects (aged 18-30 years) were seated with their dominant foot attached to a motorized arm with the knee flexed at 135°. To block external cues, the subjects wore a blindfold, earplugs, and headphones providing white noise. The knee was displaced in either the flexion or the extension direction at a velocity of 0.4°·s−1, and subjects pressed a button when they sensed motion. The knee was returned to 135°, and the test was repeated for a total of 10 trials. The PNF group received PNF stretching to the hamstrings and quadriceps of the dominant leg. The SHAM group had the dominant leg passively moved within each subjects functional range of motion. The ability to detect knee movement was retested in the PNF and SHAM groups. Pre- and posttest latencies between movement onset and subject response were analyzed. Results indicated that the PNF group had significantly increased latencies after stretching (from 2.56 ± 0.83 to 3.46 ± 1.90 seconds) compared with the SHAM group (3.93 ± 2.40 to 3.72 ± 2.15 seconds). It is concluded that PNF stretching of the hamstrings and quadriceps may acutely diminish sensitivity to knee movement. For coaches and trainers, these findings are consistent with previous reports of loss in muscle force and power immediately after stretching, suggesting that stretching just before competition may diminish performance.

Using iPads to illustrate the impulse-momentum relationship

One of the fundamental challenges in teaching is making the students able to transform course material in ways that help them solve “real world” problems.1 Sophisticated mobile technology (such as smartphones, iPads, or iTouches) offers students an opportunity to apply physics content to a broad range of scenarios to enhance their understanding and improve their class engagement. For the outlined example, students in an upper-level biomechanics class used the native accelerometers in iPads to record and analyze human movement. This activity allowed the students to experiment with the impulse-momentum relationship.