Sex Differences in Injury Mechanics

Sex vs Gender

• Sex: Biological differences between males and females.
  • Includes genetic, hormonal, and physiological differences.
  • Applies to humans, non-human animals, and cells.
• Gender: Social construct related to interpersonal roles and personal identification.
  • Unique to humans.
  • Can change over time.
  • Multifaceted and complex.

Data Gap in Sport Science Research

• Significant increase in women participating in sports and exercise over the last 70 years.
• Females are significantly underrepresented in sports and exercise science research.
• Most existing research on "humans" primarily included males, with findings generalized to females.
• Anatomical, physiological, and endocrinological differences between sexes are significant.
• IOC made recommendations for recording and reporting epidemiological data on injuries in 2020, but with little focus on female athletes (Moore et al., 2023).

Data Gap Statistics (2014-2020)

• Analysis of 5261 publications from 6 leading sport and exercise journals.
• Over 12 million participants.
  • 63% included both male and female participants.
  • 31% included male only.
  • 6% included female only.
• Participant Breakdown:
  • Males: 8,253,236
  • Females: 4,254,445
• Journals Reviewed:
  • The European Journal of Sports Science
  • Medicine & Science in Sports & Exercise
  • The Journal of Sport Science & Medicine
  • The Journal of Physiology
  • The American Journal of Sports Medicine
  • The British Journal of Sports Medicine

Factors Contributing to the Data Gap

1. Legacy:
   • Early sports research focused on male athletes, creating a male-centric bias.
2. Biology:
   • Hormonal cycles and other physiological differences make including female athletes in research more complex.
3. Opportunity:
   • Female athletes represent a smaller proportion of participants in many sports, complicating recruitment.
4. Culture:
   • Historical socio-cultural factors have led to less funding and fewer research opportunities for female sports.
5. Ethics:
   • Ethical concerns about invasive research on female athletes, especially related to pregnancy and menstrual cycles, have limited their study inclusion.
   • (Moore et al., 2023; Elliot Sale et al., 2021, Cowley et al., 2021)

Contributing Factors

• Funding and resource discrepancies in men’s vs. women’s sport.
• Higher percentage of men working in sport compared with women.
• Gender of senior authors and editorial board members affects the percentage of female participants in published papers.
• Funder of research is also important.

Enhancing Research Quality with Female Subjects

• Define participant guidelines and eligibility criteria to enhance research quality with female subjects.
• Acknowledge varied reproductive hormonal profiles in females from puberty through menopause.
• Consider the influence of exogenous factors like contraceptives and hormone therapy on a female's hormonal profile.
• Utilize standardized eligibility criteria for recruiting female participants based on their hormonal profile; confirm post-recruitment.
• Adapt experimental designs to account for menstrual cycle, contraceptive use, pregnancy, and menopause stages.
• Encourage research on the effects of estrogen and progesterone throughout a woman's life on physiology, health, and athletic performance.
• Address methodological issues such as inconsistent terminology and inadequate hormonal factor consideration to improve research consistency.

Sex Differences & Sports Injury Risk (Legerlotz & Nobis, 2022)

• Significant progress in researching female hormones, menstrual cycle, and injury risk.
• Current research oversimplifies the link between hormones and injuries.
• ACL rupture risk is higher during the preovulatory phase, but mechanisms are not fully understood.
• Mixed results in linking high estrogen levels to ligamentous weakness/laxity.
• Inconsistent effects of hormones on variables like postural control, cognition, and behavior.
• Complex relationship with multiple factors involved: physiological, biomechanical, functional, and psychological.
• Need for nuanced, interdisciplinary research.
• Reflect on biases and assumptions, consider both risks and protective effects of hormones.
• Future research should consider differences between women and investigate causation, not just correlations.

General Physiological and Anatomical Differences

• Significant variability exists within each sex.
• Not all males or females conform to average differences; individual variations can be substantial.
• Influence of these differences on movement patterns and injury risk is multifactorial.
• Can be modulated by factors such as training, conditioning, and skill acquisition.
• Understanding general physiological and anatomical differences can provide insights into potential sex-related variations in movement patterns and injury risk.
• Individual characteristics and training history should be considered when assessing an individual's movement capabilities and injury risk, regardless of sex.

Biomechanical, Anatomical, Biological Considerations

• Higher incidence in female athletes:
  • Concussion
  • ACL rupture
  • Bone stress injuries (BSI)
  • Patellofemoral pain syndrome
  • Ankle sprains (Lin et al., 2018)
• Combination of modifiable and non-modifiable risk factors.
  • Modifiable Examples:
    • Training/technique
    • Muscle imbalances
    • Nutrition
    • Neck strength, falling and landing techniques
    • Neuromuscular control
  • Non-Modifiable Examples:
    • Participation in high-risk sports
    • Anatomical structure
    • Genetics and hormonal factors
    • Developmental and aging factors
    • Neck length/head to neck size ratio
    • Pelvic width, tibial slope, Q-angle
    • Injury history

Sex, Gender and Brain Injury Risk

• Risk of brain injury in females (sex specific):
  • Biomechanics
  • Physiology
  • Neuroanatomy
  • Hormonal Factors
  • Neuropsychological Issues
  • Mental Health Issues
• Gender and cultural issues around brain injury
  • Availability of medical expertise
  • Resourcing and education
  • Societal norms and perceptions around women with brain injuries
  • Gender-based violence & abuse
• Be aware of different ways women can be injured
• Be aware of gender bias and lack of knowledge of sex differences

Female vs Male Brain Injury Risk

• Female occupants 1.5 times more likely to suffer concussion in frontal vehicle crashes (Antona-Makoshi et al., 2018).
• Females 2.6 times more likely to suffer a concussion in sport (Prien et al., 2019; McGroarty, Brown & Mulcahey, 2020).
• Differs for different sports, ages, and participation levels (van Pelt et al., 2021).
• Different head impact mechanisms in soccer (Bretzin et al., 2021) and rugby (Williams et al., 2021).

Female Brain Injury Symptom Burden

Following a brain injury, females have been reported to:

• Be more cognitively impaired than males (1.7 to 1) (Broshek et al., 2005).
• Experience greater objective and subjective concussive effects (Broshek et al., 2005).
• Have worse visual and combined memory function scores (Covassin et al., 2013; Liossi & Wood, 2009).

Female vs Male Axons

• Female axons are smaller and have fewer microtubules than male axons (Dolle et al., 2018).
• May contribute to more extensive axonal injury from comparable biomechanical forces.

Hormonal Influences

• Higher odds of a high post-concussion symptom score during childbearing years (Bazarian et al., 2010).
• Progesterone has potent neuroprotective properties (Espinoza & Wright, 2011).
• Progesterone is highest in the luteal phase (days 14-28 typically).
• 50% of concussions are sustained in the late luteal phase, no greater than 22% in other phases (La Fountaine et al., 2019).
• mTBI during the luteal phase demonstrates more significant PCS (Wunderle et al., 2014).

Cervical Spine Properties and BI Risk

• Significant differences in head and neck geometry and neck strength in males versus females (Vasavada, et al., 2008).
• Female cervical spine geometry cannot be scaled from male (Bonivtch, et al., 2006).
• Dimorphisms in spinal anatomy are linked to increased head-neck movement in vehicle collisions (Stemper et al., 2011).

Cervical Spine Properties and BI Risk

• Increased female susceptibility to whiplash & concussive injuries (Mohan & Huynh, 2019).
• Male cervical spine is better at resisting inertial loading of c-spine - greater intervertebral coupling and stability (Stemper & Derosia, 2009).
• Not just neck strength – which is significant (Salmon et al., 2013; Williams et al., 2021).

Medical Provision – New Study (2024)

• Study involved 906 NCAA athletes (61% female) who sustained a concussion and completed assessments at multiple time points.
• Recovery trajectories were similar between sexes for most measures.
  • Symptoms, cognition, and balance scores generally improved from injury to return-to-play.
• Female athletes reported higher Vestibular Ocular Motor Screen symptom scores within 24-48 hours post-injury, but not at other time points.
• While trajectories were similar, female athletes generally reported more symptoms and had some worse cognitive and balance scores across time points.
• Results suggest that apart from acute vestibular symptoms, recovery following concussion proceeded similarly in female and male collegiate athletes with similar access to sports medicine care.
• Jaclyn Caccese: "I think a lot of people will be surprised in such a large sample that women and men recover along the same trajectory…For many years, we’ve thought women took longer to recover, but evidence suggests that if women get the same access to care, they do recover similarly."

Gender Complications to Sex Differences

• Women players typically don’t have access to rugby at school – lower playing age than male counterparts (13.5 years vs 4 years for men’s and women’s university teams respectively) (Williams et al., 2021).
• Wide range of abilities in university and club teams.
• Medical provision differs considerably between men’s and women’s elite and university rugby teams.
• Culture of concussion being a "man’s injury," different symptom presentation in females may affect treatment and outcomes.

ACL Rupture

• Contact – tackle, etc., probably unavoidable.
• Non-contact – Twisting/turning, no external contact = more preventable (Chia et al., 2022).
• Approx. 5 degrees greater Q-angle in females due to wider pelvis.

ACL Injury Risk Factors (Bramah et al., 2018)

• Injured runners demonstrated greater contralateral pelvic drop.
  • Increased pelvic drop is linked to higher knee valgus moment, a known ACL injury risk factor.
• Injured runners landed with more extended knees.
  • Reduces the knee's ability to absorb impact and increases ACL strain.
• Hip adduction was greater in injured groups.
  • Increased hip adduction leads to higher knee valgus, another ACL risk factor.
• Weak gluteus medius was hypothesized to contribute to increased pelvic drop in injured runners.
  • Weak glutes can increase dynamic knee valgus and abduction moment, both ACL injury risks.

Equipment Design Reference

• Reference Human (Snyder, W. S. 1974):
  • Defined as being between 20-30 years of age, weighing 70 kg, is 170 cm in height and lives with an average temperature of from 10 to 20ºC.
  • Caucasian and is a Western European or North American in habitat and custom.

Factors Influencing Intervention Effectiveness

• Anatomical Differences

• Physiological Differences

• Biomechanical Differences

• Limited Evidence Base

• Consider known biological differences between female and male athletes.

• Does the female athlete likely respond to an exercise intervention in the same way?

• Challenging to develop an evidence-based approach.

• Review the current evidence base. If the evidence base isn't from a female cohort, how might the application of the findings differ due to…

• Consider known differences between female and male sporting environments.

• Does access to facilities, expertise, or other factors influence the effectiveness of the evidence base?

• Often interventions are less effective.

• Insufficient resources (compared to males).

• Limiting ability to apply an intervention effectively.

• Hormonal concentration fluctuations