Training as Prophylaxis: Preventing Musculoskeletal Injuries

We tend to assume that things like barbell training help us with these things, making us more resilient and less susceptible to injury, but we tend to focus on the more tangible outcomes—better numbers and bigger muscles. While lifting for strength and performance are excellent goals, we shouldn’t overlook the benefits of training for resilience and injury prevention. Knowing a little bit more about how the tissues of the musculoskeletal system get injured, we can draw some conclusions about the values of strength, conditioning, and mobility in injury prevention.

Preventing Musculoskeletal Injury

By: Nick Soleyn, PBC, Editor in Chief

There’s no evidence of the things that don’t happen to us. We may never know, for example, about the close calls and near misses that posed a real danger but left us unscathed and unaware. We tend to assume that things like barbell training help us with these things, making us more resilient and less susceptible to injury, but we tend to focus on the more tangible outcomes—better numbers and bigger muscles, mostly.

While lifting for strength and performance are excellent goals, we shouldn’t overlook the benefits of training for resilience and injury prevention. I’ve argued that training is like small doses of stress that inoculate you from the stress of life and crises. Here, I want to narrow that focus and look specifically at musculoskeletal injuries. Knowing a little bit more about how the tissues of the musculoskeletal system get injured, we can draw some conclusions about the values of strength, conditioning, and mobility as injury prophylaxis.

Economics of Musculoskeletal Injuries

Musculoskeletal injuries are a significant burden on individuals, the health care system, and the military. One paper, looking at injuries severe enough to require medical attention, estimated that, in 2000, Americans experienced more than 50 million injuries, costing about $80 billion in medical treatments and $326 billion in lost productivity (Corso 2006). Fractures alone are estimated at about 1.5 million each year, including 280,000 hip fractures and 500,000 vertebral fractures (Gitajn and Rodriguez 2011).

The additional impact on deployability has made the analysis and prevention of musculoskeletal injuries a top military priority. In 2018, musculoskeletal injuries accounted for eight million limited duty days and roughly 65% of the reasons that soldiers were deemed medically nondeployable. A 2020 paper evaluating the strategic impact of injuries on the United States Army gives us an idea of the severity of the problem: “Despite the lethality associated with combat-related trauma, [musculoskeletal injuries] unrelated to combat (in garrison and deployed settings) are the greatest medical threat to Army readiness” (Molloy et al. 2020).

In addition to these problems, the data rarely capture the additional human cost of severe injuries. Certain injuries do not just go away. They linger in the body and mind of the sufferer, causing lasting pain, leading to prolonged sedentariness, and compounding into an overall downward spiral of health and fitness. A single bad injury can lead to long-term issues with health, mobility, and quality of life.

Modifiable vs. Nonmodifiable Risk Factors

You don’t need me to tell you that injuries are bad or that injuries happen despite our best efforts. Researchers have taken that latter perspective as a necessary aspect of injury prevention. Instead of identifying risky activities, they look at types of risk and those things we can and cannot affect within our activities

Injuries follow risk, and risks come in different flavors that we call risk factors. We are familiar with risk factors from other health settings. We know that people who are overweight, do not exercise, and eat poorly are at a higher risk for hypertension, type 2 diabetes, and other chronic diseases. Those risks are often called “lifestyle risks.” But there are other risk factors, too: age, gender, and demographic put some people at a higher risk for those diseases, generally, but there’s little a person can do about those factors. Instead, higher-risk people have to make choices to mitigate risks where they have control.

Musculoskeletal injuries also have two basic categories of risk: modifiable and nonmodifiable (Lisman et al. 2017; de la Motte et al. 2017; 2019; Cameron 2010). Nonmodifiable risk factors are demographic, environmental, anatomical, and hormonal. From a risk perspective, there is little anyone can do about these things. Modifiable risk factors are often specific to the kind of risk being evaluated: safe playing surfaces, smart training, setting your safeties in lifting, and proper equipment in sports are modifiable “environmental factors.” There are also some anatomical factors that are modifiable. The chart below lists foot pronation, but you might also consider skilled biomechanics for loading and movement as an anatomical factor. Then, there are neuromuscular risk factors such as strength, fitness, and fatigue over which we have some control.

[Table. Modifiable and Nonmodifiable Risk Factors for Noncontact Anterior Cruciate Ligament (ACL) Injury Categorized as Intrinsic (I) or Extrinsic (E) and Using the Scheme Described in Several Consensus Statements10,16,17. Allen Press. Original image here (https://meridian.allenpress.com/view-large/figure/6313388/i1062-6050-45-1-58-t01.tif)]

Nonmodifiable factors set a risk baseline. Some of those risks we take on by choice. Extreme sports athletes, for example, are going to be at high risk despite being young, healthy, and active. Other factors, like age, cling to us indelibly. Preventing injuries from this perspective is all about the choices we make. To understand why these risk factors relate to musculoskeletal injuries and, by extension, the impact of our choices, let’s look at the causes of musculoskeletal injuries.

What Are Musculoskeletal Injuries, and How Are They Caused?

“Fracture and musculoskeletal injury occur when local stresses or strains exceed the ultimate strength of bones, tendons, ligaments, and muscles” (Gitajn and Rodriguez 2011).

Mechanical failure occurs when tissues of the system—bones, muscles, tendons, and ligaments—experience stress that causes them to deform, leading to fractures, strains, sprains, or ruptures. Each type of tissue responds to stress differently, according to its function.

Visually, you can see how tissues respond to forces with a stress-strain curve. Stress (on the Y-axis) is the amount of force applied, and strain (on the X-axis) is the relative measure of the deformation as a result of loading.

[The stress-strain curve of skeletal muscle. Note that the muscle does not deform in a linear fashion since its composition and structure allow it to absorb force and change shape long before it experiences failure.]

In general, a tissue’s stiffness and structure will determine the rate of deformation and its model for mechanical failure (Gitajn and Rodriguez 2011). As you might imagine, bones, being relatively stiff, do not deform much under normal loads. We would be inefficient machines if the forces our muscles produced got lost in the skeletal system, bending bones instead of moving weights, like trying to use a crowbar made of rubber. Bones aren’t brittle, however. They are rigid enough to handle loads, transfer force, and maintain their shape, but they “must also be elastic enough to absorb energy when loaded, but not so elastic that they are subject to plastic deformation” (Gitajn and Rodriguez 2011). Stiffer materials like bone have a steeper initial slope on their stress-strain curves, deforming very little under tolerable stresses, before experiencing some kind of damage. Bones will shorten and widen slightly in compression and lengthen and narrow slightly in tension.

[Caption: The stress-strain relationship for bone. The slope of the curve represents the elastic modulus of the bone. Obtained from “Experimental evaluation of new concepts in hip arthroplasty.” Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/The-stress-strain-relationship-for-bone-The-slope-of-the-curve-represents-the-elastic_fig1_224049965 [accessed 1 Sep, 2022]]

Bones also have demonstrated susceptibility to fatigue as well as a response to it, restoring microcracks when we rest. “The phenomenon of fatigue is responsible for stress fractures, which are commonly seen in athletes, like runners, who do not provide frequently loaded bones with the opportunity to repair micro-damage” (Gitajn and Rodriguez 2011). This suggests that injury prevention includes passive activities like recovery.

In comparison, muscles, tendons, and ligaments change their structural and mechanical properties in response to mechanical forces (Wang 2006). These structures change shape readily when experiencing forces. The initial stress causes immediate deformation in what is known as the “toe region” of the curve. They will then resist the stress in an almost linear fashion, deforming (or stretching) in direct resistance to the stress until they reach a failure point, where injury starts to occur. See the example of a tendon stress-strain curve below.

[Caption: A typical stress-strain curve for tendons showing defined toe, linear, and failure regions. Obtained from “Mechanoresponsive musculoskeletal tissue differentiation of adipose-derived stem cells.” Scientific Figure on ResearchGate. Available at: https://www.researchgate.net/figure/A-typical-stress-strain-curve-for-tendons-showing-defined-toe-linear-and-failure-regions_fig3_301580443 [accessed 1 Sep, 2022]]

The so-called soft tissues of the body have a number of factors that might prevent or contribute to injuries: strength, pliability, previous injury (scar tissues), pain, and support from other soft tissues (muscles taking over some of the load from tendons and tendons helping to keep the bones and muscles knitted together).

Evidence of Injury Prevention

There are many studies evaluating fitness and injury prevention; few of them are very good. Injury prevention is, unfortunately, a difficult area to study. The studies that do exist tend to compare relative performances of a given task with incidences of injury during a specified time frame. While this seems straightforward, there are a number of challenges to this type of study.

First, who is the study population? Unsurprisingly, most of these studies use military populations, which is actually pretty good. People who join the military tend to be from diverse backgrounds with varying fitness levels, but their daily tasks are relatively homogenous compared to the general population. Some studies, for example, have evaluated groups of runners and measured the injury incidence among them. Runners in the same area are not the most diverse crowd. Moreover, the people who are better at a sport might be better because they train harder, and training harder is itself a risk factor for injury. One study found that within their group of runners, fitter folks were the more likely to get injured. The researchers suggested this was because the fitter individuals participated in riskier activities (Lisman et al. 2017).

Even if you have a good population for the study, however, measuring any aspect of fitness is challenging, and measuring strength is particularly difficult. Lifters know that there is significant skill in demonstrating your maximal strength for any of the main lifts. Researchers are not coaches, and a study consisting of experienced lifters wouldn’t give good data. Instead, studies that evaluate strength often do so through single-joint exercises such as a leg extension or through isometric or isotonic holds. Those are simple enough not to mess up without practice.

If you consider the modifiable risk factors listed above, the ability to exert whole-body strength, particularly while maintaining balance and bracing your trunk, would seem to be more relevant to injury risks than a simple hold or single-joint exercise. And while a strong lifter probably has a strong leg extension, few lifters would consider the leg extension representative of useful strength, especially if the context is injury prevention in the real world.

Despite the challenges, there have been plenty of studies on fitness and injuries. One series of articles attempted to evaluate the research, separating existing studies by the fitness aspect they measured: cardiorespiratory endurance, strength and muscular endurance, and mobility. In general, poor performances tended to predict musculoskeletal injuries, with the strongest predictors being run times over a set distance (cardiovascular endurance) and push-up tests (muscular endurance), with only moderate evidence that flexibility tests could predict injuries (sit-and-reach, straight-leg raises, or ankle flexibility). Strength indicators were isokinetic ankle and knee flexion movements, isometric holds for the back, elbows, or knees, and a pull-up test. Each showed only moderate or limited evidence that poor performance predicted injury. Given the challenges listed above, it is not surprising that we don’t have definitive answers in the data. But outside of the cases where fitter people also engage in higher-risk activities, the trend seems clear. Better fitness, generally, means a reduced chance of injuries, which further suggests that fitness is a modifiable risk factor that most people can control.

Training as a Modifiable Risk Factor

The brief overview of musculoskeletal injuries should give us some confidence in the preventative power of strength training. Stronger bones and muscles are more difficult to injure. Stronger muscles also help protect our joints by limiting movements that would stress the tendons and ligaments that knit our musculoskeletal system together. By getting better at lifting weights, we do make ourselves more resilient in many ways.

But also consider some of those other modifiable risk factors. Anatomical and mechanical factors matter, too. One of the most common ways people injure their backs is by lifting real-world objects in funny ways. Flexing their spines, twisting while holding loads in their hands, trying to “lift with their legs and not their backs.” Knowing how to use your body is also an important anti-injury tactic. And it is something you learn a lot about in barbell training. You learn that your back is an important part of the kinetic chain that is unavoidably part of lifting objects. (See, e.g., “Deadlift Form Fixes: Becoming a Deadlift Machine.”)  You also learn the importance of midfoot balance and bracing properly. You build your grip and your work capacity, either of which presents injury risks if they fail prematurely.

Smart training, including good form, warm-ups, and mobility training (where appropriate) will also help prevent injuries. Barbell training’s big movements improve mobility and act as a gateway to other activities, which may improve mobility and fitness generally.

Finally, and often overlooked as a benefit of training, is the practice of recovering from bouts of stress or hard effort. The body is continually healing itself. Bones and muscles sense fatigue and use the body’s resources to repair the kinds of minor damage that occurs as a natural part of productive training. Not only does the body get better at doing this the more you train and recover, but you also get better at recognizing fatigue and engaging in good recovery practices. Good sleep, plenty of water, decent nutrition, and managing fatigue will help your training and, since fatigue is a modifiable risk factor, will help you prevent injuries outside the gym.


References

Cameron, Kenneth L. 2010. “COMMENTARY: Time for a Paradigm Shift in Conceptualizing Risk Factors in Sports Injury Research.” Journal of Athletic Training 45 (1): 58–60. https://doi.org/10.4085/1062-6050-45.1.58.

Corso, P. 2006. “Incidence and Lifetime Costs of Injuries in the United States.” Injury Prevention 12 (4): 212–18. https://doi.org/10.1136/ip.2005.010983.

Gitajn, IL, and EK Rodriguez. 2011. “Biomechanics of Musculoskeletal Injury.” Biomechanics in Applications, 36.

Lisman, Peter J., Sarah J. de la Motte, Timothy C. Gribbin, Dianna P. Jaffin, Kaitlin Murphy, and Patricia A. Deuster. 2017. “A Systematic Review of the Association Between Physical Fitness and Musculoskeletal Injury Risk: Part 1—Cardiorespiratory Endurance.” Journal of Strength and Conditioning Research 31 (6): 1744–57. https://doi.org/10.1519/JSC.0000000000001855.

Molloy, Joseph M., Timothy L. Pendergrass, Ian E. Lee, Michelle C. Chervak, Keith G. Hauret, and Daniel I. Rhon. 2020. “Musculoskeletal Injuries and United States Army Readiness Part I: Overview of Injuries and Their Strategic Impact.” Military Medicine 185 (9–10): e1461–71. https://doi.org/10.1093/milmed/usaa027.

Motte, Sarah J. de la, Timothy C. Gribbin, Peter Lisman, Kaitlin Murphy, and Patricia A. Deuster. 2017. “Systematic Review of the Association Between Physical Fitness and Musculoskeletal Injury Risk: Part 2—Muscular Endurance and Muscular Strength.” Journal of Strength and Conditioning Research 31 (11): 3218–34. https://doi.org/10.1519/JSC.0000000000002174.

Motte, Sarah J. de la, Peter Lisman, Timothy C. Gribbin, Kaitlin Murphy, and Patricia A. Deuster. 2019. “Systematic Review of the Association Between Physical Fitness and Musculoskeletal Injury Risk: Part 3—Flexibility, Power, Speed, Balance, and Agility.” Journal of Strength and Conditioning Research 33 (6): 1723–35. https://doi.org/10.1519/JSC.0000000000002382.

Soleyn, Nicholas. 2022. “What Is Flexibility? And Should You Stretch?” Barbell Logic (blog). July 29, 2022. https://barbell-logic.com/flexibility-and-stretching/.

Wang, James H.-C. 2006. “Mechanobiology of Tendon.” Journal of Biomechanics 39 (9): 1563–82. https://doi.org/10.1016/j.jbiomech.2005.05.011.

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