JRSM >
Volume 95, Number 1 >
Pp. 23-27
Army Personnel Centre, Brown Street, Glasgow G2 8EX, Scotland, UK
Note This paper is based on a report presented at a Bayer Diagnostic Prize meeting on 3 December 1998.
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The cross-gender (F/M) odds ratio for discharges because of overuse injury rose from 4.0 (95% CI 2.8 to 5.7) under the gender-fair system to 7.5 (5.8 to 9.7) under the gender-free system (P=0.001). Despite reducing the number of women selected, the gender-free policy led to higher losses from overuse injuries.
This study confirms and quantifies the excess risk for women when they undertake the same arduous training as male recruits, and highlights the conflict between health and safety legislation and equal opportunities legislation.
| INTRODUCTION |
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After the Cold War, there was increased pressure for the Armed Forces to adhere to equal opportunities legislation. This included expansion of career choices for women by opening up certain fields that had previously been reserved for males. Successive governments have acknowledged the need to increase the proportion of women in the Army to above 8%, and the widening of career choice for women was viewed as one means to achieve this.
Before 1994, female recruits were trained in single-sex establishments and the first moves towards wider integration involved bringing recruits together into mixed-sex establishments—the Army Training Regiments. Initially, female recruits were trained to a lower standard of physical fitness, but it became apparent that, as career choice widened, many female recruits were not physically capable of the job for which they had been selected. In April 1998, therefore, a system was introduced by which all recruits would be selected by use of a standard set of physical tests to score candidates in relation to their chosen career. Originally, the system was designed simply to pass or fail an applicant, but in order to assist borderline candidates a grading system was adopted to reflect a 90%, 80% and 60% chance of successfully completing initial training for their chosen trade. This grading system allowed the identification and acceptance of ‘risk candidates’ for certain trade groups.
On enlistment all recruits are medically screened before beginning the 12-week initial training programme (phase 1 training). They are trained in the basic military skills of marching, drill, weapon handling, equipment handling and field craft before being given specialist training in their chosen trade (phase 2). Such skills require a high standard of physical fitness which develops throughout the period of training. To comply broadly with sex discrimination legislation, no account is made of the physical or physiological differences between the sexes—so called ‘gender free’ training.
Numerous studies have shown military recruits to be at special risk of stress fractures, back pain, knee pain and achilles tendinitis1,2,3. The aim of this study was to record differences in the health status of recruits that resulted from a change in selection and training policy.
| METHOD |
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Although a move to gender-free training seemed likely to increase the rate
of overuse injuries in female recruits, there was no information from which to
determine the likely size of the rise. Sample size calculations were based on
the assumption of a 33% higher rate in women: this necessitated data for at
least 5472 recruits, which meant recording of discharge data for two periods
of nine months. In view of the size and repetitive characteristics of the
recruit population from year to year, age and sex matching was unnecessary.
The first period began on 1 July 1997 and ended on the final day of
gender-fair selection and training, 31 March 1998. The second period began
three months after the introduction of gender-free training, 1 July 1998, and
finished on 31 March 1999. The use of identical periods in the recruiting year
took account of seasonal recruiting patterns. Overuse injuries were recorded
directly from discharge documentation. The influence of gender on the
incidence of specified overuse injuries was examined for each corrected cohort
and the cross-gender (F/M) odds ratio for each specific injury was determined.
Statistical significance was assessed by the 
2 test and 95%
confidence intervals (CI) were calculated by Miettinen's test based
approach.
| RESULTS |
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Of 253 medical discharges from the gender-fair cohort, 104 related to overuse injuries. By comparison, the gender-free cohort had 421 medical discharges of which 160 related to such injuries. Details are in Table 2.
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Table 3 shows the gender differences in terms of incidence per 10000.
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Among male recruits overuse injury patterns changed little, but female recruits displayed a far greater tendency to overuse injury when trained under gender-free principles. The proportion of female recruits medically discharged because of an overuse injury rose from 4.6% to 11.1%, whereas the proportion of such males remained at under 1.5%. The gender odds ratio for medical discharge following an overuse injury rose from 4.0 (95% CI 2.8 to 5.7) to 7.5 (95% CI 5.8 to 9.7, p=0.001) under the new training regime—despite prior selection.
| DISCUSSION |
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Regrettably sports activity amongst adolescents has declined in recent years and this helps explain the progressive rise in injury rates amongst military recruits in general, but not the disproportionate rise in female recruits11. In an attempt to reduce the risk of injury, the Army expanded its selection tests in 1998 to give a broader picture of an individual's physical ability.
Overuse injuries have long been a feature of military training, and specific risk factors include poor physical fitness, raised body mass index, smoking, age > 24 years and excessive running1,10,11,12,13,14,15. In view of the anatomical, physiological and ergonomic differences between the sexes, gender is the single most important factor16. Jones showed that 37% of male US Army recruits experienced a lower limb injury during a 12-week basic training course12 whereas female injury rates may be as high as 60%1.
There are many reasons why female recruits are at greater risk of injury; the gynaecoid pelvis may produce a relative and transient biomechanical disadvantage when marching, running or carrying weight at the extremes of endurance17,18. Hill postulated that a mixed platoon of recruits would tend to march at the male stride (45 cm) rather than the shorter female stride (38 cm) because most of the recruits in the platoon were male19 and this led to an increased incidence of stress fractures of the public ramus amongst females. Under normal circumstances tensile stress in bone is neutralized through contraction of the surrounding musculature to induce compressive force in the bone. This neutralization is impaired when muscles are fatigued, and the unopposed tensile stress then leads to stress fractures20. Workers have shown increases in bone mineral density on completion of a 15-week training programme21; however, the strengthening of bone under stress entails initial osteoclastic demineralization at ‘cutting cones’ before trabecular meshwork restructuring and remineralization by osteoblasts22,23. The remineralization process lags behind osteoclastic resorption and takes months to complete, so that bone is weakest after 3-4 weeks of continuous training—a phenomenon demonstrated epidemiologically amongst both athletes and military recruits24,25,26,27.
Laubach researched the comparative strength of the sexes and found overlapping curves of normal distribution28, the 5th percentile for male strength approximating to the 60th percentile for women. Seemingly, however, a woman's muscle can be trained to mimic male muscle, though it takes a long period of time. A US Army study showed that the proportion of female recruits capable of passing strenuous physical tests rose from 29% to 40% after 8 weeks of basic training, yet when a similar group were trained over six months with additional resistance training, the proportion capable of achieving the test scores was as high as 78%29.
Among recruits to the British Army in 1996, there was evidence of significant muscle fatigue at the end of the first week of training, with mean increases in creatine phosphokinase of 900%30. With such evidence of excessive muscle stress at a time when bones are undergoing osteoclastic resorption it is clear why overuse injuries and stress fractures occur. For female recruits the hazard is compounded by differences in bone size, in cortical thickness and in skeletal muscle mass which interact to magnify the stress through bone by 33-39%31,32.
In summary, it is clear that there are differences in muscle physiology, bone architecture and body composition that interact to place women at a substantial disadvantage when training or working to the same output as males. In view of Laubach's overlapping distribution curves for strength, a given amount of work will require more women to reach maximum output and this will result in higher morbidity. Health and safety guidance requires employers to make allowances for these gender differences33, yet this has been overlooked in the interests of meeting equal opportunities legislation.
The question is, does one area of legislation take precedence over the other? Discrimination is allowed when being male is an ‘essential part of the job for reasons of physiology (excluding physical strength and stamina)’34. It is not entirely clear which aspects of physiology are referred to, since physical strength and stamina are clearly desirable attributes for physically demanding jobs and ‘manual handling equipment’ is not a reasonable option, for example, in the close confines of an armoured vehicle. The modern battlefield is as arduous as it has ever been and military training should reflect this.
The answer to this dilemma may lie in the interpretation of Section 51(1)c(ii) of the Sex Discrimination Act, which allows the employer to act in order to protect the woman's health if it is ‘necessary to do it in order to comply with a requirement of a relevant statutory provision (within the meaning of Part 1 of the Health and Safety at Work Act)’. The Act amplifies this provision ‘relating to pregnancy and other circumstances giving rise to risks specifically affecting women’. Whilst this paper shows that female Army recruits are at substantially greater risk of overuse injuries than their male colleagues, the injuries are not confined to female recruits. Whether Section 51 is sufficient remains to be seen.
The apparent divergence of the legislation places the Army in a difficult position. The Army has a duty to train personnel to an acceptable standard before their release to the ‘field army’, where they may be deployed on military operations. For many in the specialist trades, initial military training represents the bulk of their general military training, and to dilute the training may lessen its value and endanger personnel who subsequently find themselves on a military operation. On the other hand, it is clear that women are experiencing difficulty with the training in its current format—in short, gender cannot be ignored and rigid adherence to equal opportunities legislation is not benefiting the health of female Army recruits. The Equal Opportunities Commission Code of Practice35 encourages the use of selection tests but states that ‘tests should be reviewed regularly to ensure they remain relevant and free from unjustifiable bias’. Improving the validity of the selection tests may help reduce injury rates but at the expense of recruiting, whereas streaming according to ability within the first 2 weeks of the training course—before injury has occurred—would enable targeted remedial training to be given. Selection tests and training methods should now be reviewed in the light of these findings.
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