Sex Differences in Strength During Development: Implications for Inclusivity and Fairness in Sport.

OBJECTIVES: Males, on average, are bigger and stronger than females. Hormonal differences during puberty are one reason given for this performance advantage. However, not all evidence supports that thesis. Our aim was to further this discussion by measuring early life changes between sexes (when hormones would be similar) in components of muscle function. METHODS: Fifty-one children (29 boys, 22 girls) completed this study. Forearm muscle size and strength were assessed three times with each time point being separated by approximately a year (2021-2023). RESULTS: There was no sex*time interaction for handgrip strength (p = 0.637). There was, however, a time (p < 0.001) and sex (p < 0.001) effect. Strength increased each year and boys were stronger than girls (difference of 1.5 [95% 0.7, 2.3] kg). There was no sex*time interaction for ulnar muscle thickness (p = 0.714) but there was a time (p < 0.001) effect. Muscle size increased each year but there was no evidence of a sex effect (p = 0.12; difference of 0.81 [95% -0.21, 1.8] mm). A strong positive within-participant correlation between muscle size and strength (r = 0.803 95% CI: [0.72, 0.86], p < 0.0001) was found across time. CONCLUSION: Muscle size and strength increased together but this increase did not differ based on sex and boys were stronger than girls. Future work is needed to determine the reason for this difference in maximal strength. Any effect was seemingly present at the initial measurement (at the age of 4 years), since muscle size and strength did not change differently between boys and girls over time.

Children with Low Handgrip Strength: A Narrative Review of Possible Exercise Strategies to Improve Its Development.

BACKGROUND: Handgrip strength (HGS) is a predictor of health in both children and adults. Evidence suggests that without a possible strategy, children with low HGS may become adults with low HGS. However, little is known about what strategies are effective for children with low HGS to achieve a higher baseline level in adulthood. This narrative review aimed to investigate whether physical exercise interventions could improve HGS in children. METHODS: The relevant databases/search engine was searched using keywords related to the main topics discussed throughout this review. RESULTS: Our findings suggest that it may not be possible to improve HGS over that observed from normal development with physical education or traditional resistance-training programs. However, if the training program includes exercises that directly stimulate the forearm/hand muscle groups to grip, it may be possible to obtain changes in HGS that exceed the changes due to normal developmental growth. CONCLUSION: Although there are associations between HGS and markers of health, no research could be identified that examined whether increasing HGS would lead to an improvement in health. If an increase in HGS really does represent an improvement in long-term health, then gripping exercise may need to be included into physical activity programs during the growth/development phase.

Comparison of handgrip strength values in young children when using two different types of dynamometers.

OBJECTIVE: A Smedley hand dynamometer is one of the standard devices for measuring handgrip strength (HGS) for children and adults. The aim was to compare the HGS values using two different types of dynamometers (Grip-A or Grip-D) in young children. To enable comparison between the two devices, we have redesigned the Grip-D (i.e., modified Grip-D). METHODS: Twenty-five preschool children (10 girls and 15 boys) performed maximal voluntary HGS in the right hand using two different types of dynamometers. We ran a paired sample t-test on the difference in HGS between the two devices. RESULTS: The measured values of HGS were 9.95 kg for Grip-A and 8.56 kg for modified Grip-D, and the difference between the two devices [1.39 (SD 0.65) kg] was greater than we expected (95% limits of agreement: 0.11, 2.6 kg). Thus, we then calibrated both dynamometers ourselves using known weights. The measured values were corrected if there was an error between the known weight and each dynamometer. Following adjustment, there was still a statistical difference (p < 0.001) in HGS between Grip-A [10.65 (SD 1.52) kg] and modified Grip-D [9.98 (SD 1.85) kg]. However, the difference between the two devices was 0.67 (SD 0.69) kg with the 95% limits of agreement between -0.68 and 2.0 kg. CONCLUSION: It is concluded that the HGS values of children measured with the company-calibrated new Grip-A and modified Grip-D could provide reasonably close estimates.

Alterations in the expression of myosin heavy chain isoforms in hypoxia-induced hypertrophied ventricles in rats.

This study was designed to characterize cardiac changes in myosin heavy chain (MHC)-beta, capacity for oxidative metabolism and muscle mass in hearts of rats born and raised at simulated altitudes (2200 m or 4000 m) compared to age-matched sea level controls. On the basis of electrophoretic analyses, we found that the hypoxia-induced ventricular hypertrophy produces a significant increase in MHC-beta in both ventricles. Furthermore, we observed an exponential relationship between the mass of right ventricular muscle and percentages in the expression of MHC-beta (r=0.928, P<0.001). We also observed the reduction in the citrate synthase (CS) and 3-hydroxyacyl-CoA dehydrogenase (HAD) activities in both hypertrophied ventricles (P<0.001). As a consequence, there were negative correlations between the percentage expression of MHC-beta and the CS or HAD activities (P<0.001). In contrast, there were no significant correlations between the relative expressions of MHC-beta and either CS or HAD enzymatic activities in both ventricles after adjusting for the relative wet mass. In conclusion, the observed increases in MHC-beta may be a compensation to augment efficiency if muscles contract in hypertrophied hearts where mitochondria fail to respond to increases in tissue mass. These findings suggest that the increased relative expression of MHC-beta is a compensation to sustain cardiac contractile efficiency in response to impaired oxidative metabolism in the hypoxia-induced hypertrophied ventricles of rats.