
Why women have a diffrent injury profile then men
It is well known that women are more likely to sustain certain connective tissue injuries than men during physical activities (Jones 1998; Bijur 1997). Females injure their ACL (anterior cruciate ligament) in their knees 4-6 times more frequently than men. Females experience more ankle injuries, overuse wrist injuries and stress fractures than males. (Ristolainen 2009). Most of these injuries involve non contractile tissues such as ligaments and tendons. Where men, have higher rates of muscle strains such as groin pulls and hamstring tears compared to women.
Lets take a look at some of the differences in collegen tissue between males and females. This will set the stage for why training for injury prevention for female climbers may need to be tweaked for optimization. Most of what is common place popular training for climbing is largely taken from research done on men.
Resistance training does not produce the same effects in tendons of men vs women. Magnusson et al. found that habitual training resulted in a larger patellar tendon in men but not in women. Women have a lower rate of new connective tissue formation in tendons, respond less to mechanical loading, and have a lower mechanical strength of isolated collagen fascicles, which may leave the tissue more susceptible to certain types of injury (Magnusson 2007).
Overall, women have lower tendon stiffness which is not the same thing as general flexibility. Although females do then to have greater range of movement than men. Stiffness is a mechanical property of tissue and relates to the amount of stress or strain the tissue will tolerate before deforming and breaking. Tendons and ligaments with high stiffness will not stretch or deform as readily when strained, suggesting a lower injury riskfor the tendon or ligament (Onambéle 2007; Magnusson 2007). A study by Carroll et al. (2008) reported ~28% lower tendon stiffness in the young females and ~26% lower stiffness in the older females, compared to the male age-matched group.
A higher expression of collagen type III was found in the patellar tendons of women. Type III collagen fibers are smaller and less organized and are often associated with the repair process in injured tissue. Though in females, this is normal and not suggesting a repair process, it further shows that women have a different profile of tendon and ligament expression than men (Sullivan 1985).
The rate of collagen synthesis is lower in women than in men, which may contribute to a lower rate of tissue repair after exercise. A comparative study showed that weight-normalized patellar tendon and achilles tendon cross-sectional areas and stiffness were similar in trained and untrained female runners, yet the findings in males, trained subjects demonstrated larger stiffer tendons than untrained males. Thus, the authors suggest that the ability of achilles and patellar tendons to adapt in response to habitual loading such as running is reduced in women compared to men (Westh 2008).
The hormones impact on injury prevention
Estrogen was found to inhibit the acute exercise-related increase in tendon collagen synthesis. However, at rest, Estrogen does appear to have a stimulating effect on collagen synthesis. During prolonged inactivity women are more resistant to losing their supportive tendon structure (Kjaer & Hansen, 2008). Practically, this may mean that building in specific rest after workouts geared toward tendon traning augments tendon integrity to a greater degree in women.
Right before ovulation, women have high levels of estrogen causing the stiffness of the ligaments to decrease, the enzyme that causes cross links is limited. This time in a womens Tcycle has been linked to greater increase in ligament injuries. Testosterone does the opposite in that it increases stiffness. Increase stiffness also correlates increase rate of force development. We see men have lower rates of ligamentous injury and higher rates of force development. Yet, there are 80% fewer groin and hamstring injury in women than men in colligate soccer players. The relatively high stiffness in ligaments and tendons of men, result in the force being absorbed by the muscle resulting in more muscle injuries in men than women. Â The impact of stiffness on collegen impacts all tissues in the body that are made of collegen including blood vessles. Estrogen has a protective effect for cardiovascular disease. The aorta is made of collagen, if the aorta does not expand and stretch, it leads to higher blood pressure. The greater extensability of collegen due to the impact of estrogen leads to generally lower blood pressure protecting us from cardiovascular disease until menopause when estrogen drops. This impect of Estogen on increasing the pliability of tissue neither good nor bad but understanding the impacts gives us more power to prevent injury. One last note, Estrogen has pain inhibiting effects. Many studies acorss very diffent topics have found that women do have higher pain thresholds then men.
How does the Pill or Hormone Replacement therapy impact collagen?
Research comparing females using oral contraceptives to females not on the pill, found further insights on the impact of estrogen. Women on the pill typically maintain estradiol levels at ∼25 pg/ml without the ovulatory rise in estrogen (Mishell et al., 1972). This daily dose of estrogen and or progesterone also eliminates the cyclic rise in luteinizing and follicle stimulating hormones. However, during the early follicular phase of the menstrual cycle women have significant drop in estrogen to levels, lower than the continuous doses of estrogen offered by oral contraceptives. The women in the non-pill group tested during this phase of the menstrual cycle responded to the acute bout of exercise with an elevated collagen synthesis compared to the group taking oral contraceptives. These data furthers the idea that estradiol can influence collagen metabolism by reducing the acute exercise induced response of collagen synthesis. It also may indicate that females should train relatively more during this phase of their cycle and rest more just prior to ovulation when their estrogen levels are at a peak (Chidi-Ogbolu & Baar, K. 2019).
Long term estradiol administration (hormone replacement therapy) in post-menopausal women compared to post-menopausal women without hormone replacement found that the group receiving estradiol had higher tendon synthesis but a lower relative stiffness (resistance to strain). Animal studies found lower maximal load at tissue rupture in ACL from rabbits, which had been exposed to high estrogen levels for 1 month compared with controls. The suggestion is that estrogen therapy does impact collagen and that with estrogen in the system, tendons appear to have a lower stiffness and lower load tolerance to rupture (Slauterbeck 1999; Hansen 1985).
This discussion is to highlight that men and women are different and most of the current literature centers on men. Thus, the conclusions from much of the research may or may not be fully applicable to females. There is no value judgement as what is better, the profile of men vs women’s collagen characteristics. This is also not intended to inform anyone on the pros or cons of contraceptives or hormone replacement therapy. What it does show us is that women do differ from men and sex hormones influence our colleen and therfore our injuries.
Key Tips for injury prevention in women
Considering that women may sustain more tendon and ligament injuries, we all want to know how train to improve stiffness for injury prevention of our tendons and ligaments. Tendons adapt through mechanical stress; in other words, we need to load them. However, tendons do not respond and adapt as readily as muscles to mechanical loading. There is a sweat spot for training and though this is individual, there are differences between men and women. One study found significant increase in the mechanical and morphological properties of the muscle tendon complex of the patella tendon in both men and women training training with resistance, compared to the non-training control group. Improvements included both patella tendon volume and tendon stiffness. The difference found between sexes was the force level needed to promote these changes. For males, 90–100% maximum voluntary contraction (MVC) showed greater gains in tendon stiffness and collegen production. However, much less load what shown to generate mechanical changes in tendon stiffness for women. ~55% MVC appeared to be the cutoff point where below this level females demonstrated greater improvement in stiffness than men and above that point men had greater improvement in stiffness than women. Resistance training is the key to improving tendon integrity. When then intent of the resistance program is to prevent tendon injury by building stiffness, the exercise should be focused on a single muscle with simple movements rather than complex muli- joint exercise. Duration of loading in lab experaments has found 10 minutes is the effectve dose, after that no further stimulus is achieved. Loading programscan be done more than once a day but sessions do need to be separated by 6-8 hours.  For protective effects in healthy tendons, I recommend tendon training 3 times a week. If you are contending with an injury, multiple sessions daily may be helpful. Hoever, the loading intensity may need to be modifed to protect the injured tissue.
Check out this blog for further information on training tendon integrity
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