The most obvious difference between men and women is their physique, which translates to very large differences in physical prowess. A 2010 review by anthropologist David Puts has captured these differences.
Men are larger, stronger, faster, and more physically aggressive than women – and the degree of sexual dimorphism in these traits rivals that of species with intense male contests.
Sex differences in stature is relatively modest with men being about 10% bigger with 20% more body mass. However, these seemingly modest figures greatly underestimate the magnitude of sex differences in strength and speed, partly because women are unique among primates in having copious fat stores.
When fat-free mass is considered, men are 40% heavier and have 60% more total lean muscle mass than women. Men have 80% greater arm muscle mass and 50% more lower-body muscle mass. Men have about 90% greater upper-body strength and about 65% greater lower-body strength: the average man is stronger than 99.9% of women. In terms of anaerobic power, men have over 45% higher vertical leap and over 25% faster sprint times. Sex differences in anaerobic sprint speeds are not narrowing and some data suggest that the gap may have widened in the last decade.
Muscles are ‘organic armour’ reinforcing the integrity of the body frame: the body frame of males is substantially more robust and resilient than the female body frame. The combined effects of greater strength and constitutional resilience translates into a massive physical advantage in favour of males.
The differential system demands contribute to differences in posture, gait, muscle activity and kinematics between men and women.
The full range of sex differences in physical prowess go beyond strength and speed, into the realm of psychomotor abilities. Psychomotor abilities refer to skills that arise from brain–body coordination. These are generally classified into two categories: gross motor skills and fine motor skills.
Gross motor skills refer to large movements using large muscle groups like running, stretching, jumping and related secondary power components. The magnitude of differences in gross motor skills are as large as sex differences in physique. For example, in terms of hand-grip strength, 90% of heavily trained female athletes produce less force than 95% of untrained males.
Fine motor skills refer to small movements using small muscle groups like the manipulation of objects and making quick, accurate movements. An excellent review by Thorley and McDaniel examines sex differences in fine motor abilities that are relevant in occupational settings. In keeping with the theme, their review only included studies that involved some type of arm, hand, leg, or foot movement, and in which real objects were being manipulated. Their results reveal the following mean differences:
- Speed of Limb Movement slightly favoured men (g=0.05)
- Wrist-Finger Speed strongly favoured men (g=0.63)
- Control Precision moderately favoured men (g=0.42)
- Aiming strongly favoured men (g=0.74)
- Steadiness moderately favoured women (g=0.48)
- Multi-Limb Co-ordination very strongly favoured men (g=1.23)
- Reaction Time moderately favoured men (g=0.30)
- Motor Co-ordination slightly favoured women (g=0.25)
- Finger Dexterity moderately favoured women (g=0.37)
- Manual Dexterity slightly favoured women (g=0.19)
[The psychomotor measures, with description, can be found at the end of this post.]
However, across all the four categories which favoured women, there are two major confounds that overestimate the female advantage:
- All the measures that show a female advantage involve the manipulation of objects too small for the average male hands. For example, the female advantage appears in Pegboard tasks that use smaller pegs but disappears in the GATB M and the Large Peg measures. Indeed, it has been found that when finger size is taken into account, the female advantage is nulled, or reversed. However, data from more complex tests of dexterity where finger size is irrelevant, like the Kimura task, reveal a large male advantage.
- Age is an important variable which influences sex differences in some psychomotor measures because girls mature several years earlier than boys do. This is seen in some measures here, like in Speed of Limb Movement and Motor Coordination, where the measured female advantage is reduced or reversed among adult samples. However, in some measures where a male advantage is detected in children, the difference remains consistent, or increases, in adulthood.
Several studies investigating sex differences in visuo-motor tracking and hand-eye coordination are not included in Thorley and McDaniel’s review. For example, there is a large sex difference favouring males in pursuit precision. The male advantage in reaction time as well as their advantage in temporal processing also reveal their greater cognitive capacity.
It should be noted that studying mental abilities in isolation underestimates their real world impact. In real world settings, small measured effects may translate to very large performance advantages, especially when compounded with other domain-specific abilities. This is especially true for men whose mental abilities are setup for holistic ‘global’ processing. For example, there is a sizeable correlation between temporal processing ability (time perception), psychomotor ability and Dynamic Spatial Ability which manifests in the male advantage for throwing and intercepting.
With the confounds out of the way, men have a measured advantage in most aspects of psychomotor ability, varying according to the subskills. Many modern occupations, especially in the industrial, medical and military sectors, rely on the manipulation of objects, tools and controls. An overall male advantage is commonly reported in these domains. As with other domain-specific abilities, the male advantage in psychomotor ability also extends from their greater cognitive capacity.
Measurable sex differences in strength, speed, resilience and endurance as well as in motor control, precision and complexity can largely explain male dominance in occupational settings which rely on these traits.
Psychomotor Taxonomy, Thorley and McDaniel 2013, Table 1
|Speed of Limb Movement||Two-Plate Tapping||Subject alternately strikes two plates as quickly as possible.|
|Forearm Tapping||Subject taps a sensor as quickly as possible, using the forearm, with only the elbow moving.|
|Wrist-Finger Speed||Finger Tapping||Subject taps a sensor as quickly as possible, using a finger while the arm and hand are at rest.|
|Hand Tapping||Subject taps a sensor as quickly as possible, using the hand, with only the wrist moving.|
|Control Precision||Time Sharing||While a tracking a moving target, the subject must respond to a random number flashed on the screen.|
|Rotary Pursuit||The subject must keep a stylus in contact with a moving target on a turntable.|
|Tracking||Subject uses a joystick or a stylus to track a moving target.|
|Aiming||Marksmanship||Subjects fired real weapons at targets in a range.|
|Target Shoot Distance||Score represents accuracy of shots compared with targets on a screen.|
|Steadiness||Arm-Hand||Subject is required to keep a metal stylus from touching the sides of a small hole or the walls of a narrow maze or path.|
|Gardner||Same as above.|
|Multi-Limb Co-ordination||Two-Hand Co-ordination||Subject uses a control stick in each hand, one for horizontal movements and the other for vertical movements, to keep a gun-sight on a target.|
|NASA Langley Complex Co-ordination||Subject uses hand sticks and foot pedals to activate lights in order to match a pattern of lights given as a cue.|
|Reaction Time||Simple||Subject responds as quickly as possible to a signal (auditory or visual).|
|Choice||Similar to Simple Reaction Time, but in Choice there are two or more signals, and the subject must quickly respond to just one of them.|
|Psychomotor Vigilance Task||Similar to, if not the same as, simple RT. Subject presses a button as soon as a stimulus is activated.|
|Target Detection Time||Similar to Target Shoot Time-to-Fire. Score is derived from the time it takes a subject to press the fire key after a target appears.|
|Dynavision||Using a wall mounted board with 64 light-up buttons, subjects must press a button after it lights up and quickly respond to the next button to light up. The score is the number of correct hits in 60 seconds.|
|Target Shoot Time-to-Fire||While controlling a cursor on a screen, the subject must quickly fire on a target that will appear randomly on the screen. Score on this measure reflects the time it takes for the subject to shoot after the target appears.|
|Motor Co-ordination||Marking||Subject draws, letters, symbols, or marks of some kind in a series of spaces or boxes on a piece of paper as quickly as possible.|
|GATB K||Same as above.|
|Gibson Spiral Maze||Subject traces a line through a maze on a piece of paper, as quickly as possible, without touching the walls or any obstacles.|
|Finger Dexterity||Transfer||Small nails or pegs are quickly moved from 1 hole to another or from a basin to a hole using the fingers of one hand.|
|Assembled Parts||Includes multiple measures with similar descriptions, all of which includes simple assembly of small parts, using both hands.|
|GATB F||Similar to assembled parts, the subject puts a washer on a rivet, or removes a washer from a rivet, and repeats this process with more parts, as quickly as possible.|
|Tweezers Peg Placement||Small Pegs are moved from 1hole to another or from a small basin to a hole, using tweezers.|
|Beads||Subject is required to string small beads as quickly as possible.|
|Manual Dexterity||Hand Tool Dexterity|
|Grooved Pegboard||Similar to the Purdue Pegboard, but in this measure the pegs or holes have grooves that force subjects to turn and accurately insert the pegs, with the pattern lined up.|
|Large Peg Placement||Similar to other pegboard measures, but in this measure the peg has a thicker, easier to grasp top, to eliminate any advantage smaller hands might have.|
|Purdue Pegboard||Subject is required to place pegs in holes as quickly as possible.|
|GATB M||Subject moves pegs from one part of a board with holes in it to another.|
|Tactual Performance||While blindfolded, the subject must quickly place blocks into a form board.|
|Kimura Task||The subject completes a series of motions, including pushing a button, pulling a lever and turning a switch, as quickly as possible.|
|Product Assembly||The measure was a timed simulation of a pharmacy order, including small containers and beads. The subject had to accurately fill the containers, with the correct type and quantity of beads.|
|Cattell Pegboard||Subjects placed six pegs into corresponding holes on a board. This seems different from the other pegboards in that it is designed specifically for children.|
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