- Jul 22, 2015
..To do so, they accessed data from the National Health and Nutrition Examination Survey (NHANES), netting a little over 4,000 subjects ranging in age from 18-60. As a proxy for upper-body strength, the authors made use of the measures subjects had provided of their hand-grip strength. The participants had also filled out questions concerning their depression, height and weight, socioeconomic status, white blood cell count (to proxy health), and physical disabilities. The researchers predicted that: (1) depression should negatively correlate with grip-strength, controlling for age and sex, (2) that relationship should be stronger for men than women, and (3) that the relationship would persist after controlling for physical health. About 9% of the sample qualified as depressed and, as expected, women were more likely to report depression than men by about 1.7 times. Sex, on its own, was a good predictor of depression (in their regression, ß = 0.74).
When grip-strength was added into the statistical model, however, the effect of sex dropped into the non-significant range (ß = 0.03), while strength possessed good predictive value (ß = -1.04). In support of the first hypothesis, then, increased upper-body strength did indeed negatively correlate with depression scores, removing the effect of sex almost entirely. In fact, once grip strength was controlled for, men were actuallyslightly more likely to report depression than women (though this didn’t appear to be significant). Prediction 2 was not supported, however, with their being no significant interaction between sex and grip-strength on measures of depression. This effect persisted even when controlling for socioeconomic status, age, anthropomorphic, and hormonal variables. However, physical disability did attenuate the relationship between strength and depression quite a bit, which is understandable in light of the fact that physically-disabled individuals likely have their formidability compromised, even if they have stronger upper bodies (an example being a man in a wheelchair having good grip strength, but still not being much use in a fight). It is worth mentioning that the relationship between strength and depression appeared to grow larger over time; the authors suggest this might have something to do with older individuals having more opportunities to test their strength against others, which sounds plausible enough.
Also worth noting is that when depression scores were replaced with suicidal ideation, the predicted sex-by-strength interaction did emerge, such that men with greater strength reported being less suicidal, while women with greater strength reported being more suicidal (the latter portion of which is curious and not predicted). Given that men succeed at committing suicide more often than women, this relationship is probably worth further examination.