El poder social en la conformación de la sustentabilidad desde el patrimonio y el turismo

Lewis et a l (1986) reviewed previous work on physiological gender differences in the context of sports conditioning and summarised their findings as showing 1) little difference in the effect of different modes of progressive resistance strength training; 2) similar relative strength gains between men and women; 3) some conflict of body composition changes; 4) male and female athletes within specific events have similar muscle fibre type compositions; 5) less muscle hypertrophy is elicited in women than in men. They also concluded that aerobic exercise will benefit both men and women and that gender differences should make no difference in exercise prescription, which should be based upon individual physical work capacity.

2.7.1 Gender differences in muscle characteristics

Bishop et a l (1987) tested the hypothesis that the sex difference in muscle size, as reflected by fat-free weight (FFW) and limb fat-free cross-sectional area (FFCSA), would account for the majority of the sex difference in strength and the known

47 males and 50 females with similar long-term participation in sports activities (a group of swimmers and a group of non-athletes). After adjustment for FFW and FFCSA only upper-body strength showed significant differences. Females had much smaller upper-arm and forearm FFCSAs relative to FFW than the males, but had larger relative thigh FFCS As. FFW and limb FFCSA together accounted for 92-100% of the sex-related variance in strength for the swimmers and 95-100% for the non-athletes. They concluded that the relationship between FFCSA and FFW accounted in part for the sex difference in lower-body strength being smaller than in upper-body strength. They also concluded that once FFW and FFCSA are accounted for there are minimal sex differences in strength and upper and lower body sex differences are comparable. Bishop et al. (1989) used the same subjects to compare upper and lower body limb FFCS As of males and females after adjustment for differences in FFW. Significant differences were found for the arm and forearm for the non-athletes, but not for the swimmers. In other words, per kilogram of lean body mass, untrained women had less upper limb muscle than untrained men, but athletic females and males had the same amount of upper limb muscle per kilo of lean body mass. (Clearly, further studies are needed to verify this finding, particularly by measuring actual muscle masses or cross- sectional areas, rather than estimating them). Bishop et at. (1989) therefore supported the contention of Wilmore (1974) that the greater gender difference in upper-body strength relative to lower body strength is due to culturally based differences in physical activity. They therefore suggested that long-term activity should be considered in the design of sex difference studies, and that more research is needed to determine which of these differences are a product of biology or of culture and sample selection.

Castro et al. (1995) examined isometric strengths of the upper and lower limbs. Both upper arm and thigh torque / muscle cross-sectional area showed no significant differences between males and females. For torque per unit of mean body weight or lean body mass, large gender differences remained for the upper arm. They interpret these results to mean that differences in the absolute strength of males and females reflect differences in muscle cross-sectional areas, and conclude that gender differences in absolute strength are explained primarily by differences in the distribution of lean body mass, which they attribute to the differences caused by the adolescent growth spurt rather than prolonged gender differences in physical activity levels.

2.7.2 Gender differences in dynamic strength

Many studies have reported female and male strengths. The measures made and the resultant female : male ratios from a number of these are summarised in Table 2.14. The main lesson that can be learnt from this table is the variability of gender

differences, which is a point which has been made repeatedly in the past, by authors such as Laubach (1976) and Pheasant (1983).

Table 2.14: Summary of female : male ratios reported for dynamic strength

Study Measure f:m ratio

Laubach (1976) MAWL 59% - 84%

Hosier and Morrow (1982) Isokinetic arm strength 36%

Isokinetic leg strength 56%

McDaniel etal. (1983) ILM lift to 1.83 m 50%

ILM lift to elbow height 52%

Jacobs etal. (1988) Operational lift test (OLT) 50%

ILM lift to 1.52 m (PLT) 51%

Isokinetic lift at 0.24 m s'^ (HT) 59%

Isokinetic lift at 0.73 m s'^ (ILT) 55%

Isokinetic lift at 1.10 m s’^ (ILT) 54%

Kumar etal. (1988) Isokinetic back lifts 67-72%

Isokinetic arm lifts 66-69%

Timm (1988) Mean isokinetic strength in lift to overhead at 0.15 m s'l 51% Mean isokinetic strength in lift to overhead at 0.30 m-s'i 50% Mean isokinetic strength in lift to overhead at 0.46 m s'* 49% Mean isokinetic strength in lift to overhead at 0.61 m s'l 52% Mean isokinetic strength in lift to overhead at 0.76 m s'l 44% Mean isokinetic strength in lift to overhead at 0.91 m s'^ 42%

Bryant etal. (1990) Peak force on ILM to 1.83 m 49%

Stevenson e ta l (1990a) ELM mass to 1.83 m 53%

Peak force on ILM to 1.83 m 51%

Mean force on ILM to 1.83 m 53%

Stevenson e t al (1990b) Set style box lifting to 1.33 m 52%

Free-style box lifting to 1.33 m 56%

Ergonomic redesign box lifting to 1.33 m 64%

Weisman et al (1992) Mean isokinetic strength in lift to overhead 77%

Fothergill et al (1996) Mean hydrodynamometer strength to 1.8 m 53%

Mean hydrodynamometer power to 1.8 m 39%

Pytel and Kamon (1981) found that 94.1% of the variance in a maximum dynamic lift of a tote box could be accounted for by dynamic lift strength measured on the Mini- Gym and sex. The separate genders had high correlations (0.87 and 0.92 for 10 males and 10 females respectively) between the two measures of strength.

Hosier and Morrow (1982) compared isokinetic arm and leg strengths of 85 males and 85 females measured at 20° s"^ using Cybex devices. Gender alone accounted for 60% and 74% of the variance for the bench press (arm strength) and the leg press (leg strength) respectively. When body size and composition variables were included in the analysis they accounted for 78% and 63% of the variance of the bench and leg presses and the variance accounted for by gender was reduced to 1% and 2% respectively. Lean weight and gender made the largest contribution when stature and body diameters were controlled. Gender had the largest effect on the leg press, whereas lean weight had the largest on the bench press. This is reflected in the female : male ratios of 56% for the leg press and 36% for the bench press which can be derived from the measurements they report.

McDaniel et al. (1983) found very little overlap between male and female distributions for the ILM, with 90% of females but only 1% of males unable to lift 70 lb to 1.83 m.

Falkel et a l (1985) examined gender differences in muscular strength and endurance of the upper and lower limbs with nine males and seven females matched for mean

maximal aerobic power for both leg and arm crank exercises. They measured isokinetic strength and endurance of the knee and elbow flexor and extensor muscle groups at 30°-s"^ on a Cybex II. Gender differences disappeared for knee flexion and extension and elbow extension, but not elbow flexion, when torques were normalised by lean body weight. Further normalisation to remove the effect of differences of limb length between males and females would have further reduced gender differences. There was a significant upper to lower body strength ratio difference between the genders for elbow flexor : knee flexor strength, but not for elbow extensor : knee extensor strength. They attributed some of the lack of gender differences to the fact that they had matched the groups for aerobic power. They concluded that the ratios between upper and lower body strength appear to be related to muscle mass and are consistent for men and women, and thus women are not at a relative disadvantage in the performance of upper body strength activities. They also found the fatigue decrement during isokinetic endurance exercise to be the same for both genders.

de Koning e ta l (1985) examined the force-velocity relationship in arm flexion.

Untrained females had 38% lower maximal static moment, 43% lower maximal power, and 10% lower maximal angular velocity than untrained men. There was no difference between the males and females in the shapes of the curves. They deduced that

differences in maximal power are largely due to differences in maximal static moment, and suggested that the differences were partly due to differences in arm and muscle dimensions.

Jacobs et al (1988) showed that there were significant gender differences for the regressions of either isokinetic or ILM lifting performance on box lifting performance, but when gender and body weight were included in the regressions, the values increased from 0.93 to 0.95.

Timm (1988) found that male performance generally exceeded female performance, but females consistently exerted their peak forces at higher absolute heights than the males. If these heights were expressed relative to stature then the difference would be even greater. This implies a gender specific difference in either initial posture or lifting technique. A possible reason is males lifting more quickly than females, activating their muscles more quickly, and reaching peak strength earlier. The nature of the device may also have affected this.

Stevenson et a l (1990a) compared the genders using 37 ILM lift parameters, finding that women performed the lift more slowly, and produced less force and power. Gender differences in timing were small. Mean times were identical up to the point of

women took longer than men to complete the wrist changeover (time to second peak acceleration) and much longer to complete the lift after that. This partly reflected the fact that the women were shorter and therefore changed grip lower down and carried out the push up for longer and further than the males.

They argue that the females were at a disadvantage because they were smaller and had to start the lift at a greater percentage stature, meaning that they had less distance to accelerate the load before the wrist changeover, and had to push for a longer distance than the males. They therefore argue that the ILM was unfair to females and could have seriously underestimated female lifting potential. However, this conclusion can only be true if you wish to compare lifting relative to stature. It is emphatically not true if the ILM is used as a screening test for real tasks which have to be carried out between fixed heights. Also, McDaniel (1996) criticises their conclusion on the basis that the

difference in stature between men and women is only 8%, and lowering the starting position by 8% does not affect the test results.

Stevenson et a l (1990b) found that lifting performance of females improved relative to that of males as protocol constraints were removed. For box lifts to a height of 1.33 m, capacity was less for a 'set-style' (straight back, bent knees), than a 'free-style' protocol, and most where the subjects were permitted to carry out an 'ergonomic redesign' of the task. Correlations between box lifting and ILM performance were consistent across gender for set-style lifting where up to 50% of the variance could be predicted. Female free-style box lifting performance correlated much more poorly with ILM performance while the correlation with male performance only dropped slightly. On the ergonomic redesign' the correlation increased to 0.85 for males but became very small for females. They concluded that male lifting capabilities were reflected reasonably well by ILM tests, but falsely concluded, based upon the results of the 'ergonomic redesign', that ILM tests were poor predictors of the actual lifting capabilities of females. Stevenson et al (1996a) admitted that, in fact, males and females adopted totally different approaches to the 'ergonomic redesign', with the females constructing steps to walk up with the load while the males modified the way they handling the box. McDaniel (1996) criticises them for drawing such powerful conclusions from a sample of only 10 females and for having confounded their study design by having three different groups of subjects. To reach the conclusions they did would require differential analysis of the actual male and female techniques used in the 'ergonomic redesign' task and for the same subjects to perform the three different conditions.

Stevenson et a l (1996a) summarised their previous work in the context of using the ILM as a selection tool and its 'gender fairness'. Regression analysis showed that ILM mass and associated dynamic parameters possessed much greater power for predicting the box-lifting performance of males (R^ = 66%) than for females (R^ = 33%), with

marked differences in the independent variables retained in the regression equations. They concluded that the same linear regression model should not be used for both men and women. The accuracy of logistic discriminant analysis deteriorated as the cut-off level was raised from 18.2 kg to 27.3 kg. 33% of all female lifters were incorrectly classified by the ILM test as having failed to lift 27.3 kg on a box-lifting task. Table 2.15 lists their reasons why giving males and females the same starting and target heights creates different physical demands on them.

Table 2.15: Reasons for dissimilar physical demands on men and women caused by giving men and women the same starting and target heights for dynamic lifts. (After Stevenson er a/., 1996a)

1 Females have less distance to generate momentum in the early part of the lift. 2 Females spend more time [and distance] in the pushing phase above shoulder height.

3 Gender differences in upper-body strength are more pronounced than lower body strength (Laubach, 1976). Therefore females are at even more of a disadvantage because they spend more time [and distance] using their upper body._______________________________________________________ All the isokinetic measures of Newton etal. (1993) showed highly significant

differences between males and females. They therefore analysed and presented data separately for males and females.

Grieve (1993) measured power output over the 0.7 - 1.0 m range of 56 male and 73 female military recruits lifting from 0.4 m to chest height. He found almost no overlap between the distributions of power/weight ratios for males and females.

Fothergill et al (1996) showed that females performed dynamic exertions more slowly than males. Gender did not significantly affect the height, relative to stature, at which peak strength or power occurred. Relative to stature, males and female strengths

responded in the same way to height. Strength differences between one and two-handed exertions were greater for males than for females, and were affected by height. The mean female : male ratio for isometric strength was 0.60, and 0.76 when normalised to body weight, meaning that strength differences were larger for dynamic exertions.