1 Isotonic -a muscle fiber contraction in which force production is unchanged when the muscle contracts causing movement of an external load.  Isokinetic -a muscle fiber contraction in which force production of the contraction is sufficient to overcome the external load.
HIV/AIDS. HIV Risk Behaviors. The risk of getting HIV varies widely depending on the type of exposure or behavior (such as sharing needles or having sex without a condom). Some exposures to HIV carry a much higher risk of transmission than other exposures.
Risk by Age Group. In the United States, HIV is spread mainly through anal or vaginal sex or by sharing drug-use equipment with an infected person. Although these risk factors are the same for everyone, some groups merit special consideration because of their age. New infections are increasing among young men who have sex with men, especially young, black men men who have sex with men, for example, despite remaining steady overall.