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The purpose of this study was to determine possible differences in propulsion technique between propelling the wheelchair with and without a racket in the hand. Eight experienced wheelchair tennis players performed three submaximal exercise tests and six sprint tests on a wheelchair ergometer. Torque and velocity were measured during the tests and power output and timing variables were calculated. Differences between the conditions with and without racket were analyzed. When propelling with the racket, the racket side showed a significantly lower push time ( P = 0.03), lower percentage push time ( P = 0.001), shorter contact angle ( P < 0.001), more power loss before ( P = 0.006) and after ( P = 0.001) the push, a higher peak ( P = 0.009) and mean ( P = 0.005) power output during the push, and a lower mean overall velocity ( P = 0.03). When the same hand is compared when propelling with and without racket or when the sprint data were analyzed, similar significant differences were found. Propelling the wheelchair while holding a racket has negative effects on the propulsion technique and may lead to injuries of the upper extremity. The longer time needed to couple the hand with the racket to the rim leads to higher power losses and subsequently higher power output generation during the shorter push phase. [ABSTRACT FROM AUTHOR]

Human immunodeficiency virus (HIV) transmission models that include variability in sexual behavior over time have shown increased incidence, prevalence, and acute-state transmission rates for a given population risk profile. This raises the question of whether dynamic variation in individual sexual behavior is a real phenomenon that can be observed and measured. To study this dynamic variation, we developed a model incorporating heterogeneity in both between-person and within-person sexual contact patterns. Using novel methodology that we call iterated filtering for longitudinal data, we fitted this model by maximum likelihood to longitudinal survey data from the Centers for Disease Control and Prevention's Collaborative HIV Seroincidence Study (1992-1995). We found evidence for individual heterogeneity in sexual behavior over time.We simulated an epidemic process and found that inclusion of empirically measured levels of dynamic variation in individual-level sexual behavior brought the theoretical predictions of HIV incidence into closer alignment with reality given the measured per-act probabilities of transmission. The methods developed here provide a framework for quantifying variation in sexual behaviors that helps in understanding the HIV epidemic among gay men. [ABSTRACT FROM AUTHOR]