The aim of our study was to determine and compare the morphological characteristics of two groups of adults of different sexes and to verify the effect of sex differences in percentage of body fat on the strength and power performances of the legs and arms during short maximal exercise.
Our study reveals that male students are 7.4% (i.e. 13 cm) taller and 15.7% (i.e. 11.4 kg) heavier than female ones. Our results are comparable to those of Shephard [14] reporting that men are 13 cm taller and ≈ 14 to 18 kg heavier than women. In this line, male and female students of our study exhibit a comparable BMI (23.5 ± 2 kg/m2 and 23.2 ± 2 kg/m2, respectively). This result is in agreement with values reported by Kacem et al. [26] i.e. 23.8 kg/m2 and 22.9 kg/m2 for men and for women, respectively. We observed also that male students have a significantly lower body fat percentage than female ones (∆ F/M in %: − 45.5%). In the present study, this choice of important differences in percentage of body fat is deliberate in order to analyze the effect of sex differences in percentage of body fat on the strength and power performances. These differences are higher than those reported by Kacem et al. [26] and Shephard [14] with mean differences around 10 to 15%. In the other hand, our results reveal a significantly higher physical strength and power of both limbs in male compared to female students.
The evaluation hand gripping (HG) reflects the span of the hand and the body size [28]. However, international literature suffers from a lack of reference values for this parameter, in particular among female populations. Our results showed that male subjects performed 30.8% better than female subjects (F = 169.6, p < 0.001). This is in agreement with results reported by Angst et al. [29], according to which greater grip strength was observed in men compared to women, whatever the age.
According to Grélot (personal communication, 2020) a 39.6% sex difference in 18.5-year-old French students (i.e. male, n = 99, HG = 53.3 ± 11.7 kg vs female, n = 23, HG = 32.2 ± 6.6 kg) was measured.
In this line, Gómez-Campos et al. [30] reported significant differences between the two sexes regardless of their biological age. Sartorio et al. [31] showed that the most important factor influencing the strength of the handle seems to be always sexes, or in particular the sexual hormones. In adolescence, adipose tissue is predominant in girls while muscle mass increases considerably in boys [30]. Lean body mass is linked to sex hormones, which are more common in boys than in girls [31, 32]. Growth and testosterone have more effects on grip strength than in girls [33]. In this line, Leyk et al. [34] have shown that the strength of handful was linearly correlated with lean body mass in a large sample of German adults’ of 1654 men and 533 women Pizzigalli et al. [35] reported that height, arm length and body mass have a positive effect on hand gripping performance.
Miller et al. [17] indicate that the differences in strength linked to sex are more pronounced in the upper part of the body. Therefore, the difference in strength can be attributed to the fact that women have less lean body mass in the upper body [17]. The variations in strength and power between man and woman appear for the lower limbs as for the upper limbs when the performances are expressed in absolute values [18]. When expressed relative to body mass or to lean mass, these differences cancel out for the lower limbs while they persist for the upper limbs Weber et al. [19]. In this line, our results revealed a significant difference between male and female students’ groups for the higher (Table 2) and the lower limbs (Table 3). When expressed relative to body mass and to lean mass, these differences were reduced but persist significantly (Table 2).
Our results reveal significantly (p < 0.001) higher performances for back strength exercise in men compared to women subjects. Male students are 44.4% stronger than female ones. These results are in agreement with those reported by Koley et al. [24], in a male student population compared to their female counterparts. In addition, Koley et al. [24] reported that regardless of age, male subjects have higher average back strength values than their female counterparts. According to the same authors, back strength is positively correlated with higher testosterone levels in men. In this line, Podstawski et al. [3] and Seger and Thorstensson [11] have shown that biological maturation has a significant impact on muscle strength during puberty. In addition, during adolescence period, adipose tissue is predominant in girls while muscle mass increases considerably in boys.
Our results showed that 5JT male performance was about 23.5% better than female one (p < 0.001). Our results are in agreement with those of Kacem et al. [26] for which man produces greater power during short-term efforts. Maud and Shultz [36] state that the anaerobic power and the anaerobic capacity of men are greater than those of women. However, these observed differences decrease after normalization to body mass and vanish when normalized to lean mass. According to Kacem et al. [26], during 5JT test sex differences persist only at age of 14 years (30.4%, p < 0.001) when performance was normalized to the muscle volume of the legs and disappear at the age of adult (2.1%). Mayhew and Salm [37] suggest that anaerobic power in both sexes is related to anthropometric dimensions and the muscular strength that results from it. These same authors reported that body size and strength are the major factors explaining sex differences of the power of the lower limbs. According to Wells [38], the hormonal differentiation observed at puberty causes a substantial increase in body fat for female subjects and in muscle mass for male subjects. Similarly, Doré et al. [10] suggests that gender differences were due to the increase in total fat mass, and more specifically to the increase in lower extremity fat during puberty in girls, while boys had increased lean body mass. Kacem et al. [26] have shown that the percentage of body fat represents a factor, which disadvantages performance during brief and intense efforts (i.e. 5JT) in both young and adult women.
Since the percentage of body fat is a physical characteristic and since women generally have values of the order of 10% higher than in men, they often remain at a disadvantage [36] because they have to lift or support more unnecessary mass during jumping and racing efforts.
When ballasted, males’ performances in 5JT (11.4 ± 0.5 m) decreased by 11,8% but remained significantly (p < 0.001) higher than female performances. This corresponds to a significant (p < 0.001) reduction of 50.1% of the male vs female differences (Fig. 1).
The vertical jump (i.e. the normalized SJ) is commonly used as an index of the power of the lower limb [39]. The vertical jump performance is an important element for a successful performance in several sports. In this study, the results of the SJ revealed a significantly higher performance (+ 34.7%, p < 0.001) in male students compared to female ones.
Similarly, the power outcome during SJ of male students was 24.9% significantly higher (p < 0.001) to that of the female ones. Our results are in agreement with those reported by Abidin and Adam [40] and Hanjabam et al. [41].
According to these authors, the difference in jump performance between the two sexes is linked to the higher body fat mass in women. Even for confirmed athletes Abidin and Adam [40] reported that female have a higher percentage of body fat than male, in particular due to that stored in the hips and chest. Therefore, male athletes have the advantage to jump higher [42].
When ballasted, male performances in SJ performances (27.8 ± 2.5 cm) decreased by 10.8% but remained significantly (p < 0.001) higher than female performances (21.1 ± 2 cm). The relative difference between weighted males and females still represented 23.8% (p < 0.001) and 7.0% (p < 0.05) of the weighted male heigh and power performances, respectively. Cancelling the sex difference in fat mass by adding weight in males reduced by 31,4% and 71.7% for height and power results (Fig. 2 and 3).
Due to the action of sex hormones, gradual increase in body fat is observed in girls during maturation [9]. Hanjabam and Meitei [43], reported that the differences in anthropometric parameters are due to the sex-specific post-pubescent hormonal status. They reported a positive correlation between jump performances and body lean mass and the skeletal mass component. Furthermore, Hanjabam et al. [41] demonstrated that height, body mass and back strength performance are the predictors of SJ height.
In this line, our results showed that male students are 15,7% heavier (p < 0.001), 7,4% taller (p < 0.001) and 44.0% (p < 0.001) stronger in back strength (BS) than female students.
According to Boisseau [12], because their weaker muscular volume and their higher percentage of body fat, women physical performance can never match that of their male counterparts. In this context, Rogol et al. [44] reported that hormone production during puberty causes changes in body composition, including changes in the relative proportions of water, muscle, fat and bone. In general, boys have a significant increase in bone and muscle growth and a simultaneous loss of fat in the limbs under the influence of testosterone. In agreement with the literature, we have found that male subjects are higher, heavier and less fat than female subjects.
The ballasting of male students was accompanied by an average of 1.5 ± 0.2 m reduction of the 5JT performance (i.e. a decrease of 13.3% in performance, Fig. 1). The sex differences (∆ F/wM in %) were also reduced to 11.7% (p < 0.001). The increased carried weight by male students led to an increase in the amount of energy required to perform the jumps. These data indicate that being overweight or under fat excess impair physical performance [45]. Our results are in agreement with those of Katralli and Goudar [46] who reported that the higher the percentage of fat, the lower the performance during activities involving movement of the body. Excess weight or body fat affects performance by lowering the energy available to move each kilogram of body weight [45]. In this context, Shephard [14] reported that body composition constitutes a factor disadvantaging female athletic performance since a woman must propel a greater fat mass with less muscle mass.
Our results show that when the average percentage of fat (i.e. an inactive tissue in the force-producing system) in men is made comparable to that in women, the difference in average performance between men and women is attenuated but does not disappeared. Thus, although body fat has a substantial effect on 5JT performance, it cannot be proposed as the sole or the main factor responsible for the differences in performance observed between the sexes. Other factors may contribute to this effect. Kacem et al. [26] hypothesized that volume muscle of the lower limbs which is more important in men can be considered as the main factor responsible for the differences in performance observed between the two sexes during 5JT.
In this line, weighting of male subjects caused a decrease in sex differences of SJ performance from 34.7% to 23.8% (height; p < 0.001) and from 24.9% to 7.0% (power; p < 0.001) Cancelling the sex difference in fat mass by adding weight in male students reduced by 71.7% the sex difference in the power outcome during SJ (Fig. 2 and 3). Our results corroborate those of Davis et al. [47] who reported that the percentage of body fat in athletes was negatively correlated with jump height. In addition, these authors reported that the percentage of body fat was the best predictor of vertical jump for men aged from 20 to 37 years practicing a leisure activity. This result agrees with those of Roschel et al. [48], who stipulated that the sum of the thicknesses of skin folds is negatively correlated with the performance of vertical jumping. Since work is the product of the average force acting on the subject and the displacement of the jump, heavier athletes need more work to bring the body to the same vertical displacement as that performed by lighter athletes [49].
In our study, although reduced, the sex differences persist significantly. This supposes that factors other than the fat mass in excess contributed to the difference in performance between male and female students. Thus, other biological (i.e. morphological, neuromuscular) and/or social (level of sport participation, practiced sports, training habits) factors might be major contributors for the noted differences in strength and power performance between male and female students.