Mismatch of classroom furniture and student body dimensions: empirical findings and health implications.

PURPOSE: To examine possible mismatch between the individual body dimensions of students and the classroom furniture they use. METHODS: A total of 74 (37 male and 37 female) sixth-through eighth-grade students in a Michigan school district participated in the study; their ages ranged from 10 years, 11 months to 14 years, 3 months. Anthropometric measurements (including elbow height, shoulder height, upper arm length, knee height, popliteal height, buttock-popliteal length, and stature) were gathered in several physical education classes, each during a single session. In addition, the furniture dimensions were measured for three styles of chairs and three styles of desks prevalent in the students' classrooms. Based on both the information about student body dimensions and furniture dimensions, measures of fit or mismatch were constructed. RESULTS: The data indicate a substantial degree of mismatch between the students' bodily dimensions and the classroom furniture available to them. Fewer than 20% of students can find acceptable chair/desk combinations. Most students are sitting in chairs with seats that are too high or too deep and at desks that are too high. Even after controlling for body stature, girls are less likely to find fitting chairs. CONCLUSIONS: Based on the evidence presented, many sixth through eighth graders must endure seating arrangements in their classrooms that are not conducive to learning.

A biomechanical comparison of 7-hole 3.5 mm broad and 5-hole 4.5 mm narrow dynamic compression plates.

Seven-hole 3.5 mm broad and 5-hole 4.5 mm narrow dynamic compression plates were applied to paired canine cadaveric tibias in a stable fracture model. Paired tibias were tested to acute failure in rotation and four-point bending, and to fatigue failure in four-point bending. Resistance to screw pullout was measured for three 3.5 mm cortical screws and two 4.5 mm cortical screws inserted in the configurations of the bone plates. All plate-bone systems failed by fracture of the bone through a screw hole. The 3.5 mm plate-bone system was stronger in acute failure in rotation and in four-point bending. There was no difference in stiffness, and no difference in the number of cycles to failure in fatigue testing. Three 3.5 mm screws had greater resistance to pullout than two 4.5 mm screws. Results indicate that the 7-hole 3.5 mm broad dynamic compression plate has a biomechanical advantage over the 5-hole 4.5 mm narrow dynamic compression plate.

Clinical biomechanic correlates for cervical function: Part III. Intermittent secondary movements.

Parts I and II of this study compared kinematic and myoelectric data for two groups of asymptomatic subjects classified as having symmetric or asymmetric motor response to a palpatory test for cervical sidebending. Kinematic data revealed that asymmetric subjects had limited mobility for primary and secondary motions. Myoelectric activity was slow to be initiated in the asymmetric subjects, and reduced in time and strength of contraction. Part III addresses additional specific kinematic data concerning three-dimensional orientations of the head; however, these data were accumulated throughout the paths of movement, not just at their end points as in our previous work. Although asymmetric subjects had demonstrated significantly reduced range of motion, paths of the more minor secondary axes did not differ significantly between groups. As with previous data (Part I and II), active and passive movements were undifferentiated; this degree of likeness in even minor aspects of the motor performance continues to indicate the remarkable similarities that can exist between primary movements directed and guided by trained physicians and those actively controlled by patients themselves. Part III completes a study of cervical motor behavior in which a passive gross motion test distinguished an asymmetric group with subclinical motor behavior that has measurable kinematic and myoelectric correlates.

Measurement of crystal retarders.

We describe procedures for measuring retardation, the uniformity of retardation, and optical axis alignment of birefringent crystals.

Mechanical responses of tendons to repeated extensions and wait periods.

Tendon specimens were repeatedly extended to peak strains of either 2, 3, 4, or 6 percent. During the three 1800 s (30 min.) periods of cyclic extension, the peak loads relaxed with decreases in hysteresis and increases in slack strain. During the two 1800 s wait periods of no extension, the specimens recovered with increases in peak load and hysteresis and decreases in slack strain. However, the recovery during the wait periods was eradicated in the first few subsequent extensions and the relaxation continued as if there were no 1800 s wait periods. Stress-strain responses were well fit with power relations.

Mechanical properties of human tendon and their age dependence.

There are no previously published data on changes in the mechanical behaviors of human tendon from maturation in the second decade to senectitude in the seventh decade or thereafter. In this study, 44 tendons from individuals ranging in age from 16 to 88 yr were subjected to an extensive series of mechanical tests which included preconditioning, extensions at strain rates of 100 percent/s, 1 percent/s, and 0.01 percent/s, and stress relaxation with cyclic and constant extensions. Pairs of extensions at 1 percent/s were run throughout the protocol to evaluate the repeatability of tissue response. It was found that these responses changed little for any single sample within a pair of such tests; however, throughout the protocol, the peak stresses and moduli decreased. Extensions at different rates revealed a definite rate dependency of tendon responses with sample modulus being directly related to extension rate and slightly less hysteresis at 1 percent/s than at 100 percent/s or 0.01 percent/s. The load relaxation in samples subjected to either cyclic or constant extensions was generally best described by a linear function of the logarithm of time. The rate of relaxation with constant extension varied little with extension magnitude. The rate of relaxation in the cyclic tests was greater at 10 Hz than at 0.1 Hz. The results indicate that subject age has no effect on tendon modulus and a very small effect on hysteresis and relaxation. Extensive information on subject history was not available in this study for correlation with mechanical responses so that an age effect may have been masked by other variables, possibly health, diet, disease, or exercise.