Sex Differences in Sports Medicine

Original Editor - Josh Williams and John Rivera

Top Contributors - John Rivera, Kelley Hendrick, Michelle Lee, Taylor Lewis and Evan Thomas 

Differences in Structure

When treating patients, it is important to understand sex differences in body structure and how this could affect injury during sport. The main types of injuries that occur across both male and female sports are concussion, knee meniscal injuries, ankle sprains, strains, and fractures. Of these injuries, the most common injuries discussed are injuries to the ACL.[1]

Overall, it has been accepted that the majority of musculoskeletal injuries tend to be more sports specific rather than gender specific, but over recent years, ACL injury rates have been found to be higher in women than men.[2] This increase in rate can be attributed to extrinsic factors such as the type of sport, equipment used, environmental issues, conditioning of the athlete, skill of the athlete, and experience of the athlete. The increase in rate specifically related to body structure can be attributed to intrinsic factors such as ligamentous laxity, hormonal influences, biomechanical alignment, and intercondylar notch width. [3]

  • Ligamentous laxity has overall been found to be more prevalent in females versus males. This increase in laxity in women can be attributed to the women’s menstrual cycle due to peak levels of estrogen and progesterone or an increase in the hormone relaxin during pregnancy.[3]
  • With biomechanical alignment, women have been found to have a wider pelvis, increased Q angles, increased tibial torsion, and increased femoral anteversion. These differences in alignment between male and females has been researched, but no correlation can solely be attributed to differences in alignment. [3]
  • A smaller intercondylar notch width has been found to increase ACL injury rate. The notch width has been found to reveal much overlap between sexes and so little conclusions can be drawn about its contribution to increase in ACL injury in women.[3]

As one can see, not only are there many extrinsic factors to consider, but also several differences in intrinsic body structure and hormonal issues to consider. Due to this, it is difficult to make conclusions about one single factor increasing the prevalence of ACL injury in women. One can assume the increased prevalence in ACL injury in women is a multi factorial combination between extrinsic and intrinsic factors.

Differences in Mechanics

As eluded to above, sex differences in anatomical structure play a large role in biomechanical alignment and function. Ultimately, this impacts inherent injury risk per each gender differently. When considering whole body dynamics, biomechanical function can be grossly divided into upper and lower kinetic chains. Since current research primarily focuses on sex differences in lower extremity biomechanics, this section will predominantly examine the variances of lower quarter function in sport.

While there may be a number of movements unique to each sport, the following are commonly seen among many of athletes in some form, especially in regards to injury: running, jumping, and quick turns or direction changes.

Running

For women, running has been linked to an approximately 50% greater risk of common pathologies such as patella femoral pain syndrome (PFPS), plantar fasciitis, and iliotibial band syndrome (ITBS)[4]. Since this functional activity is inherent in many sports, it is vital for clinicians to have a comprehensive understanding of what places these athletes at risk biomechanically when developing injury prevention programs.

Some evidence has suggested that women exhibit greater adduction and internal rotation at the hip as well as abduction at the knee and ankle eversion during stance phase of running regardless varied incline or speed.[5][6] This cluster of positions is commonly referred to as a “position of risk” as it places increased valgus stress on the knee. In this position, forces are abnormally displaced to ligaments and other supporting structures of both the knee and hip joints and place the athlete at increased risk for injury. Greater velocities in the frontal and transverse planes of the hip have also been noted in women[5] as well as differences in muscle activation (e.g. gluteus medius and gluteus maximus) in response to increased pace when compared to men.[6] It is likely dependent upon the individual whether these variances are a result of or contribute to the increased joint angles described.

In terms of injury prevention, some literature currently recommends women runners should potentially consider footwear that reduces ankle eversion, and in turn increased joint angles further up the kinetic chain, since these biomechanical patterns are commonly observed[7]. Further research is needed to determine whether these biomechanical differences have an overall impact on running economy when comparing the sexes.

Landing from Jumping

One common pathology seen in sports with jumping is injury to the ACL. This can occur when there is either increased valgus stress at the knee or the athlete lands in a relatively upright position, both consequently placing increased demand on supporting structures of the knee[8]. When examining sex differences at foot contact in jumping, women typically land with decreased knee and hip flexion angles when compared to males[9][10]. When observing the complete landing phase, some evidence suggests that women tend to utilize a longer overall range of motion and more ankle musculature to help ultimately dissipate forces similarly to males. However, over the course of competition, eccentric muscle control that allows for this increased range may become more difficult to achieve due to fatigue, and in turn, greater forces are dissipated directly through the knee. Thus, this initial landing position may place females at greater risk for injuries[10].

Quick Turns or Direction Changes

Similar to jumping, quick turns and direction changes are also correlated with non-contact ACL injuries in athletes. In fact, women are up to six times more likely to incur an injury to the knee when involved in sports with these functional motions[11]. Interestingly however, evidence seems to be mixed when evaluating sex differences in kinematics.

Some studies have found female athletes exhibit greater frontal plane movement, especially knee abduction, and greater quadriceps force with cutting maneuvers when compared to males[12][13][14]. Conversely, other studies have shown only a tendency towards hip abduction in males and no variance between groups at the knee when performing this task[11]. These differences in findings likely indicate that external factors (e.g. competitive level, prior coaching on positions of risk, etc.) likely play a role in overall biomechanics with this movement. Studies involving a greater volume of subjects across varied skill level are likely need to ultimately discern how and if sex differences in mechanics contribute to the drastic difference in injury rate.

Differences in Neuromotor Control

When treating patients it is important to understand that sex can play a large roll in injury/dysfunction etiology, mechanism of injury, and treatment. One area of research that is showing to have large differences between genders and possibly causing more injuries is the neuromuscular differences in control and activation.

Neuromuscular control is comprised of detection, perception, and utilization of incoming sensory information to help perform a task[15]. In order to successfully complete a task an individual needs to coordinate the movement of multiple joints using the sensory information provided by the peripheral receptors located in and around the joints[15]. If there as an impairment within the neuromuscular component during movement it can change the pattern of movement and increase the risk of injury[15]. Unfortunately, there are injuries that occur more in females than males, and a large contributing factor has been found to be a lack of neuromuscular control.

Ligamentous injuries are commonly discussed in research on neuromuscular deficits because of the ligament dominance theory. Ligament dominance is a neuromuscular deficit that explains the imbalance between the neuromuscular and ligamentous control of joint stability, leading to too much stress being placed on the ligament structures, increasing the risk of injury. The lack of neuromuscular control causes an excess in force being placed on passive ligamentous structures of a joint, resulting in ligament sprains or tears[16].

The most common injury related to differences in the neuromuscular control is damage to the anterior cruciate ligament (ACL) of the knee. Women are at 4-6 times higher risk for an ACL injury than men[16]. It has been reported that some women who experience ACL tears have a different activation pattern of the lower extremity that may not be providing adequate control and stability of the knee joint, predisposing them to an a higher rate of non-contact ACL injury[17]. It has been reported that as muscular fatigue set in to male and female athletes, females noted a larger deficit in neuromuscular control and an increase in anterior shear at the knee joint in comparison to males, which has been connected to a higher risk of non-contact ACL injuries in women[18]. Interestingly, it was not only neuromuscular imbalances in the lower extremity that predisposed women to ACL injuries, but also trunk control. A decrease in neuromuscular control of the trunk and lower extremity in women, increased the potential for the knee to be placed in a valgus position during movement, increasing the risk of an ACL injury.

While females commonly show a decrease in neuromuscular control of the lower extremity, it is not something that can not be rehabilitated. Neuromuscular rehabilitation is a treatment program that help enhance the unconscious motor responses, by stimulating sensory signals and central mechanisms to help with dynamic joint control. This would help improve the ability of the nervous system to generate an improved muscle firing pattern and speed to increase joint stability, decrease joint forces, and to help the patient re-learn movement patterns that place them at less risk for injury[15]. Mandelbaum et al.[19] incorporated a neuromuscular training program to female soccer players prior to the season, and they noted a decrease by 88% of ACL injuries, and a 74% reduction in ACL tears[19]. This is good evidence that helping improve the neuromuscular control in females will help decrease the disparities noted among genders for ACL injuries.

Metabolic Differences

There is increasing evidence of sex-related differences in risk factors and clinical manifestation of metabolic conditions. Sex related metabolic differences are important to understand for medical treatment of men and women. Conditions such as diabetes, fat storage, and cardiac disease have an understood sex related mechanism and are conditions that have differing effects on men and women[20]. Impaired glucose and lipid metabolism as well as energy balance and body fat distribution have a great impact on overall health and can have a greater effect on women than man. This is important to understand for sport activities and particularly for sports training in men and women.

One of the biggest reasons for sports performance differences in men and women is glucose use and skeletal muscle fiber type. Women tend to have a greater proportion of Type 1 fibers and greater capillary density leading to the ability to hold of fatigue. This means better tissue perfusion and greater capacity for glucose and fatty acid oxidation. Men have a higher glycolytic capacity meaning they can burn through more glucose in the absence of oxygen, which lends itself to better performance for short-intense bursts of effort. This is related to a higher percentage of Type II fibers. This is one reason male athletes tend to be faster and stronger in athletic competition[21].

Another major difference is attributable to men’s higher testosterone levels and women’s higher estrogen levels. Testosterone is attributed to higher amounts of muscle mass and the ability to build muscle. Estrogen has been associated with better metabolic health and increased muscle sensitivity to glucose. Studies show when compared to sedentary men, endurance-trained men have 3-5 times as many estrogen receptors on mitochondria increasing the rate of glucose uptake into the muscle when activated. This also relates to men’s ability to excel at high performance events while women tend to convert fat to energy better and fatigue less [22].

Overall, efficiency of skeletal muscle energy use, fat storage, and sex hormones all play a role in men’s and women’s training.

Hormonal Differences

As discussed, sex hormones can impact the athlete in a number of ways (e.g. structure, metabolism, neuromotorcontrol, etc.). Additional hormones that may influence athlete efficiency and performance between genders include growth hormones and stress hormones (epinephrine and norepinephrine).

Growth Hormones

Growth hormones (GH) are most commonly associated in the media with doping in athletes to enhance performance via muscle hypertrophy. However, a study by Longobardi et al.[23] examines how exogenous GH use also impacts bone formation[23]. The study found men exhibited almost three times greater display of bone formation markers than women when given exogenous GH. These findings potentially have a two-fold implication in relation to sports. Since men demonstrate greatest activation of bone growth, this could potentially implicate utilization to increase healing rate and subsequent sooner return to sport[24]. On the other hand, Longobardi et al.[23] suggest identifying the cluster bone growth markers that are commonly increased could also be utilized to assist in determining if an athlete is illegally GH doping for performance[23].

Stress Hormones

Epinephrine and norepinephrine have been identified as playing an integral role in exercise adaptation. Thus, as one could infer, if inherent differences existed between men and women, this could impact performance, training, and even potentially gender affinity for certain types of sport. There is mixed evidence however in regards to this matter, and ultimately suggest that gender is only one factor impacting release of catecholamines in response to exercise[25]. Greater release of stress hormone levels release has been identified to occurred in endurance trained male athletes when compared to females; whereas, there does not seem to be a significant difference in catecholamine levels in untrained individuals in response to exercise[25]. This in turn may indicate that training level, type of sport, and other similar attributes seem to be additional contributing factors in why significant differences occur.

Epidemiology

Occurrence of injuries is common place in sporting competition and other athletic/fitness events. Common injuries that can occur include ACL injury, generalized knee pain, ankle sprain, meniscus injury, stress fractures, low back pain, patellar tendinopathy, MCL and LCL knee injury, lumbar spondylolysis, and muscle strains. Although there is no evidence to suggest that there are sex related differences in the type of injury to an athlete (only one sex getting a certain injury), there is evidence to suggest that the prevalence of certain injuries can be linked to sex (women injuring a structure more than men).

Research has found significantly higher proportion of females who engaged in basketball, volleyball, or skiing presented with an ACL injury, compared with their male counterparts. There is also a higher proportion of females than males among the track and field athletes who present with stress fractures [26]. Aside from ACL injuries, prevalence of other types of sports injuries between sexes is not well established or studied [26].

It appears lower extremity injuries are more directly correlated to a individual's sex. Research has suggested that sex hormones, dynamic neuromuscular imbalance, and anatomy play a role in the increased risk of injury in female athletes. It also appears that the effects of sex hormones on lower-extremity neuromuscular control patterns differ across the menstrual cycle phases in female athletes [27].

Female Athlete Triad

What is it?

The Female Triad is a spectrum disorder where there is an altered relationship between energy availability, menstrual function, and bone mineral density[28]. This means that the person has low amount of energy available in their body, and this depletion of energy is effecting the different body systems. The female triad is considered a spectrum disorder because there are a variety of possible presentations, and women don’t need to possess all three symptoms to be at risk for health complications[28].

Who is at risk?

This condition is commonly seen in female athletes who participate in sports that emphasize leanness and utilize high amounts of energy (ballet, gymnastics, diving, figure skating, and running)[29]. Women athletes at high school, college, and elite levels are the most at risk. The prevalence within those athletes is 1-16% with all 3 symptoms, 27% for two components, and up to 60% with one symptom of the female triad [28].

Energy Availability

The main cause of the female triad is a lack of energy availability. This occurs when a person does not have enough caloric intake based on their energy expenditure. It is not always linked to an eating disorder, but it can be a common cause of the decrease in energy intake[28]. Having a decrease in energy availability can be caused by restricting food intake, self-induced vomiting, consumption of appetite suppressants, use of laxities or diuretics, or excessive exercise demands[28][29]. This can be a deadly circumstance because health is greatly impaired when there is not enough energy present for normal physiologic functions[28]. The results of a decrease in energy can be seen in a decrease ability to recover from injury, decreased bone density, impaired menstrual function, and an increased risk for cardiovascular diseases[28].

Menstrual Function/Amenorrhea

A common side effect of the female triad is abnormal menstrual function. Women are expected to have a menstrual cycle every 28 days (+/- 7 days) for healthy a reproductive system and fertility[28]. Amenorrhea is defined as a circumstance of an absence of menstruation by the age of 16, missing three consecutive periods, or having intervals of greater than 35 days[29]. Females should consult a physician if any of these circumstances are noticed. Inadequate caloric intake in relation to exercise level puts females at risk for menstrual abnormalities because of a decrease in estrogen levels via the hypothalamic pituitary-ovarian axis[28][29].

Decreased Bone Mineral Density/Osteoporosis

The last factor and side effect of the female triad is osteoporosis. The decrease in estrogen levels, hormonal imbalances, and nutritional deficiencies can cause a low bone mass, putting females at risk of the bones becoming weaker[29]. This places the female at risk for stress fractures[28]. Estrogen is a protective hormone for bone by limiting the osteoclast activity, so a decrease in estrogen allowed the osteoclasts to be more active leading to a decrease in bone mineral density[28]. Athletes typically should have higher bone mineral density because of Wolff’s Law and the increased demands of the bone, so a decrease in bone mineral density should be a sign of an abnormality. When a female athlete has recurrent or multiple fractures, a bone scan or DEXA should be performed to evaluate the density of their bones[28].

Treatment

If a female shows signs and symptoms of the female triad, they need to seek medical treatment. The treatment of this disorder is a comprehensive multi-disciplinary approach[28]. The goal of treatment is to re-establish a menstrual cycle and enhance their bone mineral density[28]. This is achieved by a change in diet, exercise training, and increasing the overall energy availability[28]. The treatment is largely based on patient education, nutritional consults, and changing unhealthy behaviors. Medications can be prescribed if needed, oral contraceptives can help restore menstruation, transdermal estrogen helps restore hormone balances, and biophosphates can be used to help with the resultant osteoporosis[28]. The female triad can be linked to depression, low self-esteem, and anxiety disorders, so further referrals may be needed for mental health[28].

Pregnancy and Sport

When discussing sex-related issues in the sports realm, it is important to take into consideration how pregnancy could affect athletes. Most research on this topic addresses the issue of pregnancy within the later high school years and the collegiate athlete population. Not only does pregnancy have a significant affect on the pregnant female athlete, but also male athletes.

Recent statistics reveal that 74% of athletes were sexually active in the last 12 months and 40% of males and 53% of females admitted to being sexually active in the last 30 days. Even with these staggering statistics, it was found in one study that only 1% of female athletes expressed experiencing pregnancy versus 11% of female non-athletes. Although statistics show that sports participation does reduce the pregnancy rate, we cannot ignore the staggering percentage of athletes who are currently sexually active and it is important to address this issue. [30]

Furthermore, we have to take into consideration how pregnancy affects both female and male athletes. The NCAA has made a major commitment to gender equality with the Model Policy. The Model Policy supports all athletic departments to end pregnancy discrimination. This policy states that male athletes and their pregnant partner are allowed to maintain all scholarship benefits and other health benefits and are entitled to the same fair treatment. [31]

Another major issue to consider with pregnancy is the health of the female athlete and how that would affect her participation in sports. Pregnancy changes the female athletes anatomical and physiological mechanisms with weight gain, increased lordosis, reduced balance, and increased ligamentous laxity being said to be some of the major contributors. Because of these changes, it is important to consider contraindications and warning signs to exercise for pregnant women, which are stated as follows:

Absolute Contraindications [32]

  1. Pregnancy induced hypertension
  2. Restrictive lung disease
  3. Incompetent cervix
  4. Risk for premature labor
  5. 2nd or 3rd trimester bleeding
  6. Placenta praevia after 26 weeks gestation
  7. Ruptured membranes                                                  

Relative Contraindications [32]

  1. Severe anaemia
  2. Cardiac arrhythmia
  3. Chronic bronchitis
  4. Type I diabetes
  5. Morbid obesity
  6. Extremely underweight
  7. Sedentary lifestyle
  8. Orthopedic limitations
  9. Seizure disorder
  10. Thyroid disease
  11. Heavy smoker

Warning Signs [32]

  1. Vaginal bleeding
  2. Dyspnea before exertion
  3. Dizziness/headache
  4. Chest pain
  5. Muscle weakness
  6. Calf pain or swelling
  7. Preterm labor
  8. Decreased fetal movement
  9. Amniotic fluid leakage

Based on these contraindications and warning signs, the U.S. Department of Health and Human Services offers physical activity guidelines for pregnant women that should be taken into consideration by athletes. Guidelines state that pregnant women who have been involved in high intensity aerobic exercise, such as those involved in aerobic type sports, can continue exercise during pregnancy as long as they discuss this with their health care provider and are aware of the warning signs and contraindications. Moreover, athletes who are involved in sports with high risk for falling or abdominal injury should continue with caution and avoid these types of activities. Lastly, pregnant women should also avoid participating in supine exercises after the first trimester. [33]

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