Low ponderal index is associated with decreased muscle strength and fatigue resistance in college-aged women.

Poor fetal growth is associated with decrements in muscle strength likely due to changes during myogenesis. We investigated the association of poor fetal growth with muscle strength, fatigue resistance, and the response to training in the isolated quadriceps femoris. Females (20.6 years) born to term but below the 10th percentile of ponderal index (PI)-for-gestational-age (LOWPI, n=14) were compared to controls (HIGHPI, n=14), before and after an 8-week training. Muscle strength was assessed as grip-strength and as the maximal isometric voluntary contraction (MVC) of the quadriceps femoris. Muscle fatigue was assessed during knee extension exercise. Body composition and the maximal oxygen consumption (VO(2)max) were also measured. Controlling for fat free mass (FFM), LOWPI versus HIGHPI women had ~11% lower grip-strength (P=0.023), 9-24% lower MVC values (P=0.042 pre-trained; P=0.020 post-trained), a higher rate of fatigue (pre- and post-training), and a diminished training response (P=0.016). Statistical control for FFM increased rather than decreased strength differences between PI groups. The PI was not associated with VO(2)max or measures of body composition. Strength and fatigue decrements strongly suggest that poor fetal growth affects the pathway of muscle force generation. This could be due to neuromotor and/or muscle morphologic changes during development e.g., fiber number, fiber type, etc. Muscle from LOWPI women may also be less responsive to training. Indirectly, results also implicate muscle as a potential mediator between poor fetal growth and adult chronic disease, given muscle's direct role in determining insulin resistance, type II diabetes, physical activity, and so forth.

Indirect peer aggression in adolescence and reproductive behavior.

Evolutionary psychologists have suggested that indirect aggression during adolescence is a strategy to compete with same-sex peer rivals for resources, status, and mating opportunities. We collected survey data on 143 young adults to determine retrospectively, the amount of indirect aggressive behavior they perpetrated and the amount of indirect victimization they experienced in middle school and high school. We also collected information about reproductive opportunities such as age at first sexual intercourse and number of lifetime sex partners to determine whether aggression or victimization could be used to predict measures of reproductive opportunity. We performed a principal components analysis to develop factors from 16 aggression and victimization variables. Results indicate that females who reported indirect aggression toward peers had earlier ages at first sexual intercourse and females who were more victimized in adolescence experienced later ages at first sexual intercourse. We discuss these results in terms of intrasexual competition and evolutionary theory.

Handgrip strength and socially dominant behavior in male adolescents.

Handgrip strength (HGS) is highly heritable and a good overall measure of strength and muscle function. Indicative of blood testosterone levels and fat-free body mass, HGS is also highly sexually dimorphic. Recent psychological research shows that HGS is correlated with a number of social variables, but only in males. We conducted three studies to further investigate the relationship between HGS and measures of aggression and social competition among adolescents. Consistent with previous reports, correlations were almost exclusive to males, but this was only visible during late adolescence (i.e., high school). These findings support evolutionary hypotheses regarding grip strength in male-male competition and suggest that similar to measures of testosterone, HGS is a measure that is predictive of social behavior in older adolescent males.