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Assessing Fitness for Military Enlistment: Physical, Medical, and Mental Health Standards
Studies have identified biomechanically relevant differences between genders in the knee,3 back,4 shoulder,5 hip,6 elbows,7 and fingers.8
While biomechanically related risk is multidimensional, several factors may help to explain the greater risk of musculoskeletal disorders for women. First, differences in muscle mass and the mechanical advantage of the muscles relative to the joint have been reported for the back, with women generally at a biomechanical disadvantage (Janssen et al., 2000; Jorgensen et al., 2001, 2003a; Marras et al., 2001). Differences in muscle line of action are associated with differences in the muscle origin and insertion in women and typically provide less mechanical advantage and greater muscle (and joint) loading (Jorgensen et al., 2001). Similarly, studies of the knee joint muscle mass have also indicated reduced muscle mass and a muscle mechanical advantage in women (Suzuki et al., 1996; Wretenberg et al., 1996; Csintalan et al., 2002; Wojtys et al., 2003).
Second, there are differences in the bone and ligamentous tissue size and response as a function of gender. Within the knee joint, Besier and colleagues (2005) found that the knee contact area of women compared with men was significantly smaller when flexed but similar at full extension. In addition, men have slightly greater cartilage thickness (Eckstein et al., 2001). Similarly, differences in the size and bone density of vertebral bodies have been documented between men and women, with women having reduced size (Gilsanz et al., 1994a, 1994b; Ebbesen et al., 1999; Marras et al., 2001). Ligamentous creep response also appears to differ between men and women, with women exhibiting greater creep (and less stability) especially when the knee is flexed at 35 degrees (Chu et al., 2003).
Significant biomechanical differences in neuromuscular response between genders have also been documented in the literature. Granata and colleagues (2002) have noted reduced stiffness in the quadriceps of equivalently trained women compared with men. This would indicate reduced
See Johnson et al., 1979; Carlson et al., 1996; Wretenberg et al., 1996; Cao et al., 1998; Kerrigan et al., 2000; Eckstein et al., 2001, 2002; Hudelmaier et al., 2001; Kaufman et al., 2001; Wojcik et al., 2001; Csintalan et al., 2002; Granata et al., 2002; Manninen et al., 2002; Chu et al., 2003; Wojtys et al., 2003; Baker et al., 2004; Blackburn et al., 2004; Besier et al., 2005; and Sbriccoli et al., 2005.
See Gilsanz et al., 1994a, 1994b; Ebbesen et al., 1999; Lindbeck and Kjellberg, 2001; Marras et al., 2001; Davis et al., 2002; and Jorgensen et al., 2001, 2003a, 2003b.