Injuries in the sport of racewalking.

OBJECTIVE: To examine the nature and incidence of injuries suffered by racewalkers. DESIGN AND SETTING: A total of 682 questionnaires were distributed to racewalkers in the San Diego/Long Beach, CA area, participants in a national qualifying race held in Washington, DC, and subscribers to The Ohio Racewalker. SUBJECTS: Four hundred questionnaires were returned to the investigators, for a return rate of 58.7%. MEASUREMENTS: Questions addressed demographics, exercise patterns, competitive history, walking surfaces, types of footwear normally used for training and competition, and injuries suffered during racewalking. Questionnaire results were tabulated and chi-square analyses were used to test for interrelationships. A stepwise discriminant analysis was used to develop a model for the prediction of injury in racewalking. RESULTS: Racewalking participation peaks in the 30- to 39-year-old age group, while the proportion of injured participants is greatest in those under 30. Most injuries involved the lower extremity, but the "average" racewalker suffered only one serious injury every 51.7 years. Those participants who trained six or seven times per week were most likely to be injured; those who trained three or fewer times per week were least likely to be injured. The percentage of injured participants increased progressively with weekly training mileage. A model based on the data from this investigation correctly predicted membership in either the injured or uninjured group in only 64.1% of cases and is, therefore, of limited use to the researcher or clinician. CONCLUSIONS: Although the rate of injuries in racewalkers is low, more systematic research is necessary before sports medicine professionals can confidently recommend consistently effective injury prevention procedures.

A comparison of prehension force control in young and elderly individuals.

Age-related changes were investigated in the control of precision grip force during the lifting and holding of objects with slippery (silk) and nonslippery (sandpaper) surface textures. Two groups of active elderly adults comprising individuals aged 69-79 years (n = 10), and 80-93 years (n = 10) together with a group of young adults aged 18-32 years (n = 10) participated in the study. Each subject lifted a free weight (3N) during which time gripping and lifting forces were monitored. The elderly subjects, especially the individuals in the 81-93 year group, had a larger number of fluctuations in the grip force rate curve and longer force application time than the younger subjects during lifting. The effect of prior experience with one surface on the following different surface was more pronounced in the younger subjects than the elderly subjects. These results suggest a decline in programmed force production capacity with increased age. The fingers of the elderly subjects were more slippery and they exhibited a greater safety margin of the grip force while holding the object than the younger adults. The overall results demonstrated that precision grip force control capacity declines with advancing age. It is suggested that this decline is due mainly to age-related changes in skin properties, and cutaneous sensibility functions, and in part to central nervous system function.

The mechanical properties of the heel pad in elderly adults.

The shock absorbing characteristics of the heel pad in vivo were examined in two groups of active elderly individuals whose ages ranged between 60 and 67 years (n = 10) and between 71 and 86 years (n = 10). For comparative purposes, young adults (n = 10) aged between 17 and 30 years were also examined. A free-fall impact testing device which consisted of an instrumented shaft (mass 5 kg), accelerometer and position detection transducer was used to obtain deceleration and deformation of the heel during impact. The data were obtained from impact velocities of 0.57 m.s-1 (slow) and 0.94 m.s-1 (fast). Peak values of the deceleration and deformation, as well as the time to these peaks from onset of impact, and energy absorption were evaluated. At the slow impact velocity, no age effect was found for the parameters examined except for the energy absorption. At the fast impact velocity, there was higher peak deceleration and smaller deformation for the elderly than for the younger adults. The energy absorbed was less for the elderly than for the younger adults. It was concluded that the capacity for shock absorbency of the heel pad declines with age.

Absolute angle measurement using the earth-field-referenced hall effect sensors.

A miniaturized absolute angle sensor utilizing Hall generators referenced to the Earth's ambient magnetic field has been developed. The sensor has three-dimensional angular sensitivity which allows the output to be self-normalized resulting in high immunity to both B-field and temperature induced errors. The individual Hall generator elements were operated with a final sensitivity of 4.07 V G-1. The Earth's field, magnitude 0.486 G with a surface declination angle of 58.2 degrees (San Diego, California), was used as the excitation/reference field. Bandwidth limiting, low-noise design, and active/passive thermal compensation techniques were employed resulting in a sensor bandwidth of DC to 100 Hz with a maximum signal-to-noise ratio of 44.5 dB. The maximum angular resolution of the sensor was measured to be +/- 0.27 degrees. Temperature induced error was measured to be less than 2% from 25 degrees C to 40 degrees C. The measurement of shoulder joint rotation was used as the test case application for the sensor with excellent agreement between theoretical and experimental performance.

Aerobic Dance Injuries: A Survey of Instructors.

In brief: The authors surveyed 135 instructors about the incidence of injuries and associated factors related to aerobic dance. The instructors had a high number of overuse injuries. Many instructors and students were dancing on nonresilient surfaces and were wearing inappropriate shoes. Many instructors may have exceeded their limits of tolerance to mechanical impact shock trying to maintain high levels of aerobic exercise.

Purine modulation of methotrexate cytotoxicity in mammalian cell lines.

The modulation of MTX cytotoxicity by purines has been studied in a number of mammalian cell lines. In each case, it was found that exogenous purines (guanosine, deoxyguanosine, adenosine, deoxyadenosine, and hypoxanthine) both reduced and potentiated MTX cytotoxicity depending on the MTX concentration. At low MTX concentrations (less than 6 X 10(-8) M), purines reduced MTX toxicity and at higher concentrations they potentiated MTX toxicity. The reduction of low-concentration MTX cytotoxicity by purines was associated with the reversal of MTX-induced changes in deoxyribonucleotide pools. On the other hand, potentiation of MTX toxicity by purines was associated with substantial increases in deoxyadenosine 5'-triphosphate levels in conjunction with low deoxythymidine 5'-triphosphate levels. The magnitude of increase in deoxyadenosine 5'-triphosphate levels tended to correlate with the degree of potentiation which varied between 5-fold and 200-fold, depending on cell type and the exogenous purine.

Biochemical and cell cycle perturbations in methotrexate-treated cells.

The effects of methotrexate (MTX) in the presence or absence of exogenous thymidine (dThd, 10(-5) M) or hypoxanthine (Hx, 10(-4) M) on cell cycle kinetics and deoxyribonucleoside triphosphate pools (dNTP) were studied in cultured human leukemic T-cells (CCRF-CEM). MTX cytotoxicity was found to increase linearly with drug dose for MTX concentrations between 10(-9) M and 10(-7) M. No further increase in cytoxicity was observed with much higher MTX concentrations (10(-7) M-10(-4) M). A similar dose-response relationship was found for both MTX-induced inhibition of DNA synthesis and changes in dTTP and dGTP pools but not for either MTX-induced inhibition of purine synthesis or changes in dATP and dCTP pools. Exogenous dThd reduced MTX cytotoxicity, at all MTX concentrations examined, but Hx reduced cytotoxicity only at MTX concentrations less than 6 X 10(-8) M and potentiated toxicity with higher MTX concentrations. This potentiation of cytotoxicity was accompanied by substantial elevation of dATP pools. In all instances where dThd or Hx reduced MTX cytotoxicity, a concomitant increase in both dTTP and dGTP levels and in the rate of DNA synthesis was observed. These results suggest a close correlation between MTX-induced alterations of dNTP and inhibition of DNA synthesis and subsequent MTX cytotoxicity. The possible modulation of MTX cytotoxicity by purines is discussed.