3.2.2. Muscular Strength

Muscular strength and power are important contributors to physical fitness with an independent role in the prevention of many chronic diseases and early deaths [147]. The aging process results in decline of muscle mass and strength by about 1% per year starting in the fourth decade [148]. Peak instantaneous power declines by approximately 7% per decade when assessed via vertical jump test in endurance runners, in sprinters as well as in the general population, and very similar are reported for ergometric lower extremity power testing [36,144,149,150]. Muscle wasting, however, differs largely between individuals due to differences associated with the aging process per se but can be significantly modified by PA levels and exercise training. Most important characteristics associated with aging are the muscle architecture and fiber type composition, tendon properties and vascular control of the contracting muscle [147,151]. In athletes, the onset of declining powerlifting performance is more pronounced and progresses more rapidly than endurance performance, i.e., men's and women's power-lifting performance starts decreasing by 3% per year in the 4th decade and by 1% per year thereafter [152]. As shown for endurance training on cardiovascular fitness, rapid and pronounced effects of resistance training on muscle mass, muscle strength and power are well established in young and elderly individuals as well [147]. Accordingly, higher levels of muscle strength and power in the aging athletes are not surprising but seem predominantly due to hypertrophy of remaining fibers as the loss of fiber numbers seems not to be preventable by lifelong PA [153]. The magnitude of differences between sexes in muscular strength is well documented and may almost entirely be explained by the difference in muscle size of equally trained men and women [154], indicating similar muscle quality characteristics for both sexes. The overall muscle mass and power is greater in men than women and the absolute changes in muscle mass following resistance training are also larger in men, but the relative changes in strength and muscle hypertrophy are similar in both sexes [155]. From a cross-sectional study including a wide age range of men and women, better preservation of eccentric peak torque and enhanced capacity to store and utilize elastic energy with aging was shown for females compared to males [156]. While eccentric actions in a hypertrophy-targeted resistance training seem to be slightly more effective than concentric actions, both types of training should be included [157]. Skeletal muscles of males compared to females are generally stronger and more powerful, but muscles of males might be more easily fatigable. While those sex differences are primarily caused by differences in contractile mechanisms, other mechanisms, e.g., muscle perfusion, voluntary activation, etc., also represent contributing factors (Figure 4) [158].
