Sex Differences In Strength Research Articles

Sex Differences in Neuromuscular Adaptations Following 12 Weeks of Kettlebell Swing Training.

The purpose of this study was to investigate whether there are sex differences in strength, power, and muscular endurance gains following a 12-week kettlebell swing protocol. Twenty-eight men (29.4 ± 7.3 years; 176.4 ± 6.2 cm; 80.1 ± 11.0 kg; 146.0 ± 22.3 kg in deadlift; 1.8 ± 0.2 kg/body mass deadlift relative strength) and 25 women (32.3 ± 5.5 years; 162.5 ± 7.5 cm; 66.2 ± 9.7 kg; 92.4 ± 17.3 kg in deadlift; 1.4 ± 0.2 kg/body mass deadlift relative strength) participated in this study. Measures of strength in the deadlift, power in the countermovement jump, muscular endurance in the deadlift, and workout of the day (WOD) were obtained before and following six and 12-week time points. Both sexes showed pre- to post-test differences in strength (p < 0.001; one repetition maximum (1RM) improvement of 12.6% for men and 11.7% for women), power (p < 0.001; jump height improvement of 12.9% for men and 6.8% for women), and muscular endurance deadlift test (p < 0.001; improvement in deadlift repetitions of 24.5% for men and 29.2 for women), and only men improved performance in DT WOD (p < 0.001; WOD improvement of 21.3% for men and 1.3% for women). Furthermore, men had greater gains in the power test (p = 0.02) and in the DT WOD endurance test (p = 0.04). Kettlebell training appears to be an effective strategy for increasing strength, power, and endurance in both men and women, but considering the lower responses in power and DT WOD, other strategies should also be considered to optimize women's results in these tests.

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

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. 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). 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. 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.

Sex differences in strength, functional capacity and mobility in patients with multiple sclerosis: An exploratory analysis

BackgroundPhysical exercise programs are commonly designed without consideration for sex differences. Nevertheless, disease progression exhibits sex-specific patterns, resulting in different functionality and strength performances. ObjectivesTo analyze sex differences in strength, functional capacity, and mobility, and to evaluate sex-dependent differences in leg strength in multiple sclerosis (MS) patients. MethodsA cross-sectional study was conducted with 35 participants (female: n = 19; Expanded Disability Status Scale (EDSS)= 3.0 ± 1.2, male: n = 16; EDSS= 3.3 ± 1.2). Body composition, maximal voluntary isometric contraction (MVIC), explosive strength (rate of force development, RFD), central activation ratio (CAR), functional capacity, and mobility were assessed. ResultsDifferences were observed between males and females (p = 0.001) in height, lean body mass and MVIC. No differences were observed in the other variables. Regarding the leg asymmetry, men showed higher values in the stronger leg for both MVIC (p < 0.001, d=large) and RFD, whereas women showed higher values only in RFD. Men with MS demonstrated a greater capacity to produce maximal strength than women with this disease. ConclusionsThe results found suggest that maximum strength differs between men and women in our sample of patients with multiple sclerosis. Furthermore, the weaker leg, regardless of sex, exhibits poorer results in explosive strength compared to the stronger leg. However, maximum strength only shows differences in men and not in women. Therefore, these findings should serve as a basis for rehabilitation professionals when planning training programs for this population.

Substantial but Misunderstood Human Sexual Dimorphism Results Mainly From Sexual Selection on Males and Natural Selection on Females.

Human sexual dimorphism has been widely misunderstood. A large literature has underestimated the effect of differences in body composition and the role of male contest competition for mates. It is often assumed that sexually dimorphic traits reflect a history of sexual selection, but natural selection frequently builds different phenotypes in males and females. The relatively small sex difference in stature (∼7%) and its decrease during human evolution have been widely presumed to indicate decreased male contest competition for mates. However, females likely increased in stature relative to males in order to successfully deliver large-brained neonates through a bipedally-adapted pelvis. Despite the relatively small differences in stature and body mass (∼16%), there are marked sex differences in body composition. Across multiple samples from groups with different nutrition, males typically have 36% more lean body mass, 65% more muscle mass, and 72% more arm muscle than women, yielding parallel sex differences in strength. These sex differences in muscle and strength are comparable to those seen in primates where sexual selection, arising from aggressive male mating competition, has produced high levels of dimorphism. Body fat percentage shows a reverse pattern, with females having ∼1.6 times more than males and depositing that fat in different body regions than males. We argue that these sex differences in adipose arise mainly from natural selection on women to accumulate neurodevelopmental resources.

Sex differences in glenohumeral muscle activation and coactivation during a box lifting task

Manual material handling is associated with shoulder musculoskeletal disorders, especially for women. Sex differences in glenohumeral muscle activity may contribute to women’s higher injury risk by affecting shoulder load and stability. We assessed the effects of sex (25 women vs 26 men) and lifting load (6 kg vs 12 kg) on muscle activation during box lifting from hip to eye level. Surface and intramuscular electromyography were recorded from 10 glenohumeral muscles. Most muscles were more activated for the heavier box and for women. These effects were larger for ‘prime movers’ than for stabilisers and antagonists. Despite their apparently heterogeneous effects on muscle activity, sex and mass did not affect Muscle Focus, a metric of coactivation. This may be partly related to the limited sensitivity of the Muscle Focus. Nevertheless, sex differences in strength, more than in coactivation patterns, may contribute to the sex imbalance in the prevalence of musculoskeletal disorders. Practitioner summary: We studied sex differences in glenohumeral muscle activity in a lifting task to eye level. Women lifting a 6-kg box activated their muscles similarly to men lifting a 12-kg box, i.e. up to 48% of their maximum capacity. Interventions minimising shoulder load should be implemented, especially for women. Abbreviations: BB: biceps brachii; DeltA: anterior deltoid; DeltL: lateral deltoid; DeltP: posterior deltoid; DoF: degrees of freedom; ED: effect duration; EMG: electromyography; ES: effect size; Infra: infraspinatus; Lat: latissimus dorsi; MF: muscle focus; MMH: manual material handling; MVA: maximal voluntary activation; Pect: pectoralis major; Subscap: subscapularis; Supra: supraspinatus; TB: triceps brachii

The Report of the Military Leadership Diversity Commission: An Inadequate Basis for Lifting the Exclusion of Women from Direct Ground Combat

The recommendation of the Military Leadership Diversity Commission to lift the exclusion of women from ground combat is deeply irresponsible and cannot be taken seriously. The Commission’s lodestar was diversity, not military effectiveness, and it failed to take into consideration a wealth of information bearing on its recommendation. The Commission’s recommendation was based primarily on sources that cannot be considered authoritative, and the Commission’s analysis of the sources that it did consult was superficial and in conflict with some of the facts, as opposed to the “spin,” contained in these very sources. The Commission substantially downplayed the sex difference in strength and other physical capacities, striking down the straw man that “all women lack the physical ability to perform in combat roles,” but never addressing how many women there are who actually possess that ability, a piece of data that is highly relevant to its recommendation. Moreover, the MLDC report does not mention the word “pregnancy,” despite the fact that there is much data to suggest that pregnancy has substantial adverse effects on deployability and readiness even with the ground-combat exclusion in place. Finally, the Commission’s conclusion that there was “little evidence” that integration of women has had a negative impact on cohesion and performance ignores not only a wealth of information to the contrary in sources it did not consult, it also ignores a great deal of evidence to the contrary in the sources that the Commission actually did consult.

Muscle function and fatigability of trunk flexors in males and females

BackgroundOptimal function of the abdominal muscles is necessary for several life functions including lifting and carrying tasks. Sex differences in strength and fatigability are established for many limb muscles and back extensor muscles, but it is unknown if sex differences exist for the abdominal muscles despite their functional importance.MethodsEighteen females (24.3 ± 4.8 years) and 15 males (24.1 ± 6.6 years) performed (1) isometric trunk flexion maximal voluntary contractions (MVCs) in a range of trunk positions to establish a torque-angle curve and (2) submaximal (50% MVC), intermittent isometric contraction (6 s on, 4 s off) until task failure to determine fatigability of the trunk flexor muscles. Dual X-ray absorptiometry quantified body fat and lean mass. Physical activity levels were quantified with a questionnaire. Torque-angle curves, electromyography (EMG), MVC torque, and torque steadiness were compared with repeated measures ANOVA with sex as a between-subjects factor.ResultsFor the torque-angle curve, MVC torque was reduced as the trunk angle increased toward flexion (p < 0.001). Males had greater MVC torque than females at the extended positions (31% difference), with no sex differences in torque in upright sitting (p > 0.05). Time-to-task failure for the submaximal fatigability task in upright sitting was similar between males and females (12.4 ± 7 vs 10.5 ± 6 min). Time-to-task failure was positively associated with strength (r = 0.473, p = 0.005) and self-reported physical activity (r = 0.456, p = 0.030). Lean mass in the trunk was positively associated with trunk flexor strength (r = 0.378, p = 0.011) and self-reported physical activity (r = 0.486, p = 0.007). Finally, torque steadiness [coefficient of variation of torque (CV)] during submaximal isometric contractions decreased with contraction intensity and was similar for males and females across all intensities.ConclusionsUnlike many limb muscle groups, males and females had similar fatigability and torque steadiness of the trunk flexor muscles during isometric contractions. Stronger individuals, however, exhibited less fatigability. Lower self-reported physical activity was associated with greater fatigability of trunk flexor muscles. The relationship between strength and fatigability of the trunk flexor muscles and physical activity supports the importance of abdominal muscle strengthening to offset fatigability in both males and females.

Sex Differences in Strength and Power Support the Use of a Mixed-Model Approach to Resistance Training Programing

POWER IS IMPROVED THROUGH INCREASING VELOCITY OR FORCE AND IS CORRELATED WITH ATHLETIC SUCCESS IN MEN AND WOMEN ACROSS SPORT AND COMPETITIVE LEVEL. MAXIMAL FORCE CONTRIBUTES MORE TO POWER OUTPUT THAN VELOCITY. HOWEVER, WOMEN PRODUCE LESS FORCE AND GREATER VELOCITY THAN MEN WHEN COMPARED WITH SIMILAR RELATIVE INTENSITIES. THEREFORE, A MIXED-MODEL TRAINING APPROACH (MMTA) TO PROGRAMING THAT EMPHASIZES FORCE PRODUCTION MAY BE OF BENEFIT TO WOMEN. BY IMPLEMENTING EXERCISE-SPECIFIC OPTIMAL LOADS, AN MMTA MAY INCREASE POWER AND ATHLETIC SUCCESS. THE PURPOSES OF THIS ARTICLE ARE TO (A) EXPLORE SEX DIFFERENCES IN POWER, AND (B) DETERMINE THE EFFICACY OF MMTA TO PROGRAMING.

Sex Difference in Strength and Size Ratios between Reciprocal Muscle Groups in the Lower Leg

This study compared strength and size of reciprocal muscle groups in the lower leg between sexes. 20 young men and 14 young women volunteered as subjects. Joint torques developed during isometric maximal voluntary plantar flexion (TQPF) and dorsiflexion (TQDF) were measured using a dynamometer. Muscle volumes of plantar flexors (MVPF) and dorsiflexors (MVDF) were determined by magnetic resonance imaging. In each of the muscle groups, joint torque was significantly correlated with muscle volume in young men and women (r=0.610-0.848) and the y-intercept of the regression line between them was not significantly different from zero. Based on these observations, the dependencies of muscle strength ratio on muscle size ratio between the plantar flexors and dorsiflexors were investigated using joint torque and muscle volume. The correlations between the MVPF per MVDF and the TQPF per TQDF were significant both in young men (r=0.608) and women (r=0.773), suggesting that strength ratio is strongly affected by size ratio between the plantar flexors and dorsiflexors in young men and women.

Academic Apartheid: Segregation in the Study of Partner Violence

The study of men’s violence against their intimate partners is segregated from the study of other forms of violence. Comparing intimate partner violence (IPV) to other violence, however, allows one to examine whether the motivation and the legal response are similar. I examine whether men’s assaults on partners are particularly likely to have a control motive, whether women’s assaults on partners are particularly likely to be motivated by self-defense, and whether intimate partner violence is less likely to be reported to the police and legally sanctioned. The evidence casts doubt on the feminist approach, which has dominated the study of IPV. I suggest that a theory of instrumental violence provides a better understanding of IPV. Such an approach recognizes a variety of motives and emphasizes the role of conflict in intimate relationships, sex differences in strength and violence, and the importance of chivalry. Finally, I suggest that social scientists who study IPV should be more careful in their descriptive terminology.

Lateralised processing of positive facial emotion: sex differences in strength of hemispheric dominance

Sex differences in lateralisation have been examined frequently, but have found varying and contradictory results. The experiment presented in this paper examines the lateralisation of processing positive facial emotion in 276 right handed undergraduates (138 males, 138 females). All participants completed two behavioural tests of lateralisation: a handedness preference questionnaire and a chimeric faces emotion judgement task, which measured strength of lateralisation for the perception of positive facial emotion. A highly significant difference was found for the chimeric faces task only: males were more strongly lateralised than females, although both males and females tended to be right hemisphere dominant. The results suggest that females are more bilaterally distributed and hence have greater access to mechanisms located in each hemisphere.

Sex Differences in Ratings of Perceived Exertion and Muscle Pain During Eccentric Contractions

1515 Few studies have examined sex differences in ratings of perceived exertion (RPE) and muscle pain during eccentric exercise. This is problematic due to the importance of eccentric contractions to functional activities and reports of lower RPE and muscle pain during eccentric contractions compared to concentric contractions. PURPOSE: To examine sex differences in RPE and muscle pain intensity and unpleasantness during eccentric isokinetic contractions. METHODS: Men (n = 34) and women (n = 40) aged about 20 years (SD = 2.20) completed eccentric strength testing with the elbow flexors of their dominant arms to determine their 5 repetition maximum (5RM). Then they completed 3 sets of 12 eccentric repetitions at 90°/s with a preload of 16% of 5RM and 60 s rest periods in between each set. Differentiated RPE (CR-10 scale) and pain (0–100 numerical scales) were assessed immediately after strength testing and each set. RESULTS: Two-way (Sex × Set) ANOVAs indicated that RPE, F2,144 = 30.92, pp < .01, η2 = .30, pain intensity, F2,144 = 31.98, pp < .01, η2 = .31, and pain unpleasantness, F2,144 = 22.23, pp < .01, η2 = .24, increased across the sets. A main effect for Sex was observed for RPE, F1,72 = 4.29, pp = .04, η2 = .06, but this effect was absent when total work across the three sets was a covariate, F1,71 = 0.34, pp = .58, η2 < .01. No other main effects or Sex by Set interactions were observed. In addition, comparisons of the women and men with RPEs between 9 and 10 for the first, second, or third sets (ns = 28–31) did not show a significant sex difference in average percentage of peak torque produced. CONCLUSION: Lower RPE for women than men during eccentric contractions has been reported, but we did not detect such a difference. In addition, we did not observe sex differences in muscle pain during eccentric contractions, which contradicts a previous report of lower muscle pain in women than men. However, such sex-related comparisons may be affected by the method of controlling for sex differences in strength and the parameters of the eccentric contractions preformed (e.g., velocity). This investigation was supported by a NIAMS postdoctoral research fellowship (F32 AR08623-02) to Erin A. Dannecker, Ph.D.

Sex Differences in Ratings of Perceived Exertion and Muscle Pain During Eccentric Contractions

1515 Few studies have examined sex differences in ratings of perceived exertion (RPE) and muscle pain during eccentric exercise. This is problematic due to the importance of eccentric contractions to functional activities and reports of lower RPE and muscle pain during eccentric contractions compared to concentric contractions. PURPOSE: To examine sex differences in RPE and muscle pain intensity and unpleasantness during eccentric isokinetic contractions. METHODS: Men (n = 34) and women (n = 40) aged about 20 years (SD = 2.20) completed eccentric strength testing with the elbow flexors of their dominant arms to determine their 5 repetition maximum (5RM). Then they completed 3 sets of 12 eccentric repetitions at 90°/s with a preload of 16% of 5RM and 60 s rest periods in between each set. Differentiated RPE (CR-10 scale) and pain (0–100 numerical scales) were assessed immediately after strength testing and each set. RESULTS: Two-way (Sex × Set) ANOVAs indicated that RPE, F2,144 = 30.92, pp < .01, η2 = .30, pain intensity, F2,144 = 31.98, pp < .01, η2 = .31, and pain unpleasantness, F2,144 = 22.23, pp < .01, η2 = .24, increased across the sets. A main effect for Sex was observed for RPE, F1,72 = 4.29, pp = .04, η2 = .06, but this effect was absent when total work across the three sets was a covariate, F1,71 = 0.34, pp = .58, η2 < .01. No other main effects or Sex by Set interactions were observed. In addition, comparisons of the women and men with RPEs between 9 and 10 for the first, second, or third sets (ns = 28–31) did not show a significant sex difference in average percentage of peak torque produced. CONCLUSION: Lower RPE for women than men during eccentric contractions has been reported, but we did not detect such a difference. In addition, we did not observe sex differences in muscle pain during eccentric contractions, which contradicts a previous report of lower muscle pain in women than men. However, such sex-related comparisons may be affected by the method of controlling for sex differences in strength and the parameters of the eccentric contractions preformed (e.g., velocity). This investigation was supported by a NIAMS postdoctoral research fellowship (F32 AR08623-02) to Erin A. Dannecker, Ph.D.

Hormonal factors in the development of differences in strength between boys and girls during adolescence: a longitudinal study

The development of elbow flexor (biceps) and knee extensor (quadriceps) strength has been followed in a mixed longitudinal study of 50 boys and 50 girls from the age of 8 to 17 years. Sex differences in strength emerged at the time of peak height velocity and were especially marked for the biceps. Data for individual children were aligned to the time of peak height velocity and associations between strength, height, weight and circulating testosterone were investigated using multi-level modelling. The results show that, for girls, quadriceps strength is proportional to height and weight while for boys there is an additional factor which can be fully attributed to increasing levels of testosterone. Testosterone is important in explaining differences in biceps strength between the sexes but an additional factor is also required. It is suggested that, in addition to a direct effect on muscle, testosterone could have a second indirect action on biceps strength by promoting growth in length of the humerus as part of the general development of the male upper limb girdle.

The influence of task resistance on the characteristics of maximal one- and two-handed lifting exertions in men and women.

Dynamic lifting strength was assessed at lift velocities ranging from 0 to 1 m.s-1 using a hydrodynamometer in which the viscous resistance to motion could be preset. Nine men and nine women performed one- and two-handed dynamic exertions against low, medium, and high resistances. The subjects were required to lift as forcefully and as fast as possible from a height of 400 mm to just above head height. The instantaneous forces recorded at knee, knuckle, hip, shoulder, elbow, and head heights were compared with those obtained during maximal one- and two-handed isometric lifts performed at the same heights. The position of peak force relative to stature was lower for one-handed lifts (35.9% of stature) than for two-handed lifts (38.4% of stature) (P < 0.005), but was unaffected by lift resistance (P > 0.05) and subject sex (P > 0.05). Lifting forces during two-handed exertions were on average 1.5 times greater than for one-handed exertions (P < 0.0001). However, the difference in the strength of one- and two-handed lifts was highly dependent on hand height (P < 0.0001) and task resistance (P < 0.005), and was greater for the men than for the women (P < 0.001). When static lifting strength was measured at heights relative to stature and normalized by dividing by body weight, there was no significant difference in performance between the men and the women [mean normalized female:male: (f:m) strength ratio = 0.76, P > 0.05]. Under dynamic conditions the sex difference in lifting performance was pronounced (mean normalized f:m strength ratio = 0.68, P < 0.01), especially for power output (mean f:m power.unit body weight-1 ratio = 0.52, P < 0.005). The proportion of generality (r2 x 100) between dynamic and static lifting strength was found to range between 63% and 87%. These data suggest that the dynamic and static tests of lifting strength measured a common, intrinsic ability to produce maximal lifting forces. The finding that sex differences in strength are dependent on whether the exertion is static or dynamic has important implications for biomechanical models of human strength.

Muscle strength from adolescence to adulthood--relationship to muscle fibre types.

The aim of the present study was to reinvestigate muscle strength and the relationship to muscle fibre and the level of physical activity in adult men and women previously studied during adolescence. A group of 55 men and 26 women were tested for maximal strength (handgrip, Sargent jump and two-hand lift) and completed a questionnaire concerning physical activity during their leisure time (activity index) at the ages of 16 and 27 years. Biopsy specimens were taken from the vastus lateralis and analysed for fibre type (percentage of I, IIA, IIB) and fibre area (area I, area IIA, area IIB). The sex differences in strength increased from age 16 to 17 years. Body dimension, sex, percentage of type II, mean fibre area and the activity index contributed to explaining 50-75% of the strength at both ages. Different changes in relationship between fibre type composition and strength in women and men was seen with increasing age. In the women, the relationship between strength and the percentage of type II fibres changed with age (from 16 to 27 years of age) from a positive correlation (only Sargent jump) to negative correlations for all the strength tests, i.e. the more type I fibres the stronger the subject. A positive correlation between strength and the level of physical activity during leisure time was revealed in the women at both ages. The positive correlation between strength and type II fibres in the 16-year-old men had disappeared at age 27. No systematic relationships between strength and the level of physical activity were seen in the men at either 16 or 27 years of age. It is suggested that women may be more dependent on physical activity than adult men to develop strength and the percentage of type I fibres reflects the degree of physical activity among adult women but not among adolescent women.

Residual impairment in handgrip strength after unilateral frontal-lobe lesions

The handgrip strength of 65 normal control subjects and 166 patients with unilateral frontal-or temporal-lobe excisions was assessed. Because of the known sex differences in strength, the results for the men and women were analysed separately. The grip strength of men with left frontal-lobe lesions was found to be within the normal range, but women with comparable excisions from the left frontal lobe had a residual impairment in strength on both hands. The men with right frontal-lobe lesions had a significant reduction in the strength of only the left hand, and the women in this group displayed a similar tendency. The deficits were interpreted in terms of a loss or disruption of input from the premotor area to the primary motor cortex.

Sex Differences in Strength and Fatigability

The pattern of fatigue resulting from systematically varying the intercontraction rest interval was examined in male (N = 14) and female (N = 15) subjects employing a hand-grip fatigue exercise of 5 min duration. The contraction was maintained for 3 s, and the rest interval varied between 1, 2, 3, and 4 s, the order randomly assigned each subject. The fatigue bouts were separated by at least one week, and all testing was performed on a BLH load cell and recorder. No significant differences existed in initial maximum strength for either males or females over the four testing conditions, but significant differences did occur in final strength and absolute and relative endurance for both groups. The female subjects were significantly lower than males in initial and final strength, and absolute endurance. However, the females had significantly more relative endurance than males. The fatigue curves were two-component exponentials, with a half-time decay for the main component of 116 s for the males and 80 s fo...

Sex differences in strength. Some implications for the design of handtools : Pheasant, S.T., and Scriven, J.G. In: Proceedings of the Ergonomics Society's Conference 1983, Edited by K. Coombes. Taylor & Francis Ltd, London, 1983, pp 9–13

Sex differences in strength. Some implications for the design of handtools : Pheasant, S.T., and Scriven, J.G. In: Proceedings of the Ergonomics Society's Conference 1983, Edited by K. Coombes. Taylor & Francis Ltd, London, 1983, pp 9–13

Sex differences in strength — some observations on their variability

One hundred and twelve datasets, which allowed a direct comparison of the strengths of men and women, were located in the published literature. For each of these, three indices of sex difference were calculated: the ratio of the mean female strength to the mean male (F/M), the proportion of the total variance in strength attributable to sex (R 2) and the “percentage of chance encounters between members of the opposite sex in which the female is stronger” (%CEFS). Sex difference was shown to be very variable, the values of these indices being both task and population specific. An experiment was conducted in which male and female subjects gripped and turned knurled cylindrical handles of 10, 30, 50 and 70 mm diameter. Maximum isometric torques were recorded. Sex differences became more pronounced as handle size increased. The optimal handle-size was 50 mm for both male and female subjects. Data concerning whole body exertion (Pheasant et al, 1982) were also analysed for sex differences. It was concluded that very similar tests of strength could exhibit very different levels of sex difference. The task or equipment designer should not make assumptions about sex differences in strength for a particular action, but should rely on empirical investigation.