Individual and cumulative measures of knee joint load associate with T2 relaxation times of knee cartilage in young, uninjured individuals: A pilot study.

BACKGROUND: Articular cartilage structure and chondrocyte health are sensitive and reliant on dynamic joint loading during activities. The purpose of this pilot study was to determine the association between measures of individual and cumulative knee joint loading with T2 relaxation times in the knee cartilage of young individuals without knee injury. METHODS: Twelve participants (17-30 years old) without history of knee injury or surgery completed MRI, physical activity (PA), and biomechanical gait testing. T2 relaxation times were calculated in the cartilage within the patella and lateral and medial compartments. Accelerometry was used to measure mean daily step counts, minutes of PA, and % sedentary time over 7 days. Vertical ground reaction force, external knee joint moments and peak knee flexion angle were measured during stance phase of gait using three-dimensional motion capture. Cumulative knee joint loading was calculated as daily step count by external knee joint moment impulse. The relationship between measures of knee joint loading and T2 relaxation times was assessed using Pearson correlations. RESULTS: Higher T2 relaxation times in the femoral and tibial cartilage were consistently correlated to greater body mass, daily step counts, moderate and vigorous PA, and peak knee joint moments (r = 0.10-0.84). Greater cumulative knee flexion and adduction loading was associated with higher T2 relaxation times in the femoral and tibial cartilage (r = 0.16-0.65). CONCLUSION: Preliminary findings suggest that individual loading factors and cumulative knee joint loading are associated with higher T2 relaxation times in the articular cartilage of young, healthy knees.

Chemical contrast observed in thermal images of blood-stained fabrics exposed to steam.

Thermal imaging is not ordinarily a good way to visualize chemical contrast. In recent work, however, we observed strong and reproducible images with chemical contrasts on blood-stained fabrics, especially on more hydrophobic fabrics like acrylic and polyester.

Effects of exercise using industrial respirators.

Respirators (respiratory personal protective devices), used for protection against occupational toxic exposures, may impose flow resistance and dead space respiratory loading. Effects of exercise level, a 300 mL deadspace and single respirator cartridge inspiratory load were determined in ten healthy volunteers. Subjects tended to limit peak work rate (pressure generated and pressure X flow) and to prolong the inspiratory portion of the respiratory cycle due to respirator use. O2 consumption and heart rate were not significantly affected. The qualitative response was not affected by exercise level. During submaximal exercise, normal subjects did not reach their compensation limits for the variables studied.

Estimation of the exertion requirements of coal mining work.

The work requirements of coal mining work were estimated by studying a group of 12 underground coal miners. A two level (rest, 300 kg X m/min) test was performed to estimate the linear relationship between each subject's heart rate and oxygen consumption. Then, heart rates were recorded during coal mining work with a Holter type recorder. From these data, the distributions of oxygen consumptions during work were estimated, allowing characterization of the range of exertion throughout the work day. The average median estimated oxygen consumption was 3.3 METS, the average 70th percentile was 4.3 METS, and the average 90th percentile was 6.3 METS. These results should be considered when assessing an individual's occupational fitness.