Knee extensor strength differences in obese and healthy-weight 10-to 13-year-olds

Abstract

The purpose of this study was to investigate if obese children have reduced knee extensor (KE) strength and to explore the relationship between adiposity and KE strength. An observational case-control study was conducted in three Australian states, recruiting obese [N = 107 (51 female, 56 male)] and healthy-weight [N = 132 (56 female, 76 male)] 10- to 13-year-old children. Body mass index, body composition (dual energy X-ray absorptiometry), isokinetic/isometric peak KE torques (dynamometry) and physical activity (accelerometry) were assessed. Results revealed that compared with their healthy-weight peers, obese children had higher absolute KE torques (P ≤ 0.005), equivocal KE torques when allometrically normalized for fat-free mass (FFM) (P ≥ 0.448) but lower relative KE torques when allometrically normalized for body mass (P ≤ 0.008). Adjustments for maternal education, income and accelerometry had little impact on group differences, except for isometric KE torques relative to body mass which were no longer significantly lower in obese children (P ≥ 0.013, not significant after controlling for multiple comparisons). Percent body fat was inversely related to KE torques relative to body mass (r = -0.22 to -0.35, P ≤ 0.002), irrespective of maternal education, income or accelerometry. In conclusion, while obese children have higher absolute KE strength and FFM, they have less functional KE strength (relative to mass) available for weight-bearing activities than healthy-weight children. The finding that FFM-normalized KE torques did not differ suggests that the intrinsic contractile properties of the KE muscles are unaffected by obesity. Future research is needed to see if deficits in KE strength relative to mass translate into functional limitations in weight-bearing activities.

Obesity-related differences in neuromuscular fatigue in adolescent girls

“…Indeed, it is likely that the level of voluntary torque produced during MVC partly accounted for the greater peripheral fatigue and earlier exhaustion in obese girls. As expected (Tsiros et al 2013), obese girls produced higher absolute KE torque than their normal weight counterparts. Interestingly, we demonstrated here that this higher force production capacity was positively correlated to the peripheral fatigue development (i.e., Qtw pot decrement).…”

“…Despite this lack of consensus regarding the rate of fatigue development in obese people, we suggest that obese individuals could fatigue to a greater extent than their normal weight counterparts because of (i) their higher absolute strength/power capacity (Abdelmoula et al 2012;Maffiuletti et al 2013;Tsiros et al 2013) and (ii) their potentially higher amount of fast-fatigable muscle fibers (Kriketos et al 1997;Wade et al 1990). Indeed, it has been shown that the higher neuromuscular fatigue of healthy men vs. women was no longer observed when subjects were matched for absolute MVC force (Hunter et al 2004), suggesting that the higher the MVC force, the higher is the muscle fatigue.…”

The bigger, the stronger? Insights from muscle architecture and nervous characteristics in obese adolescent girls

“…In obese girls and boys, higher absolute KE force values have been reported compared to non-obese (19)(20)(21)(22). This has been ascribed to a greater total fat-free mass in obese (e.g.…”

“…This has been ascribed to a greater total fat-free mass in obese (e.g. (22)), but also to a higher relative force (i.e. normalized to segmental muscle mass; (19)).…”

“…Increased total fat free mass is frequently observed in obese preadolescent and adolescent (19,21,22), but this variable does not exclusively reflect the contractile tissue (19,21,22,24). Only one study has studied the effect of obesity on the lower limb muscles hypertrophy and found a comparable KE anatomical crosssectional area (ACSA) in obese compared to non-obese adolescents (24).…”