By Tammy Kovaluk, MTI Contributor
Tactical athletes need to perform high level tasks while carrying additional load. Law enforcement personnel, search and rescue, and firefighters all carry loads that are typically 20kg, typically as high as 40kg (5). Military soldiers bear the highest loads, well over 45kg (100+ pounds), a likely cause of the increased injury rates (2, 5).
There is considerable data on load carriage related injury rates, particularly in military soldiers, perhaps partially because of the cost associated. The average cost of musculoskeletal injury amongst military soldiers is $2.5 billion per year, with estimates as high as $3.6 billion per year (9). This amount includes all cost-associated injuries, however, research indicates a large percentage of these injuries are from load carriage, accounting for 45% of injuries amongst US combat forces during a 12-month deployment (7). According to Szivak, load carriage is the largest contributor to musculoskeletal injury, exceeding injuries due to enemy contact (10).
Military soldiers undergo load carriage for extended periods of time, along with intensive anaerobic periods, as they do not have the relatively close support networks as with the police or fire service (5). This is likely another reason the injury rates are relatively higher. It also affects combat capability. During WW2 for example, significant numbers of American troops deaths occurred in the water during landing at Omaha Beach due to carrying high loads (5). In 1983 in Grenada, large numbers of US soldiers were so overloaded they were unable to continue fighting, left on the roadside (5).
I would argue that both search and rescue and wildland firefighters often undergo extended load carriages. However, research is lacking in these areas and is largely focused within military soldiers.
This purpose of this article is to:
a) Share some common research findings for load-carriage related injuries and risk factors.
b) Share a critical analysis of some literature for minimizing risk of load-carriage related injury through strength and conditioning. This is an area of specialist interest of mine, as I personally know many veterans who suffer long term load carriage related injuries, have heard amongst recruiters that injury rates are increasing in boot camp, and sustained a back injury myself, attributing this largely due to training errors.
Summary: Load Carriage Common Injuries and Injury Risk
Common Injuries
Research indicates the leading causes of load-carriage injuries include the lower extremity (knee, ankle, and foot, at 40.3%) and the spine (at 39.0%) of all injuries, with 82.3% of all injury types being “overuse injuries” (1, 5). These injuries are the number one reason both male and female soldiers have not been able to complete a march (5). Females experience twice the rate of foot injuries and suffer significantly more severe back injury (5).
Fatigue increases injury risk.
Commonly reported in research, fatigue associated with load carriage leads to increased energy cost, and biomechanical alternations. Gait patterns, ground impact forces, and spinal load alterations are all factors that increase risk of injury, especially during prolonged and/or high intensity load carriage. (1,2,5). Walking with a backpack load increases forward lean, generating vertebrae stresses, intervertebral discs, muscles, and other spinal structures (1,5). Both heavier loads and time on feet are related to increased fatigue and risk of injury. Research has not indicated the difference in intensity (ie walking vs running) with load carriage and injury rates. I would think this would be important factor consider, as running alone increases compressive forces.
Sufficient physical fitness is important.
All research found indicates that underlying fitness, in terms of both aerobic and strength, is important. For example, a study observed musculoskeletal injury rates amongst 67,525 recruits between 2012 and 2014 during Basic Training at San Antonio (1). They concluded that lower levels of fitness amongst the arriving recruits, particularly aerobic fitness, correlated to increased injury rates and severity (1).
Prior injury increases risk of future load carriage injuries.
It appears a previous load carriage-related injury increases future injuries by approximately 50%. In a study by Orr et al., for example, 34% of 338 military soldier respondents reported at least one load carriage-related injury, and 52% of those experienced repeated load carriage injury after suffering a previous load-carriage injury (7).
Other reported factors
- BMI (body mass index). Molloy and colleagues found that a lower BMI had increased risk of injury, as the load is relatively high compared to body weight, as well as those with a combination of a higher BMI and low physical fitness (1).
- Muscular deficiencies. Certain muscular deficiencies – particularly decreased trunk flexion strength, decreased trunk extension strength, and decreased knee extension strength – have been correlated with increased injury amongst load carriage of lower extremities and spinal injury (1).
A critical analysis of some literature related to minimizing risk of load-carriage related injury through strength and conditioning.
Since TSAC (Tactical Strength and Conditioning Facilitator) has become a specialist branch within the NSCA (National Strength and Conditioning Association), strength and conditioning considerations for tactical athletes have been of greater interest. The NSCA now has a “TSAC” report, with primary and secondary articles, TSAC conferences, and a specialized certification available.
However, despite finding ample research on load-carriage injury rates with promising article titles, the literature on strength and conditioning approaches for minimizing risk of injury was extremely limited. According to Orr, what is lacking are practical guidelines on how to effectively condition military personnel for load carriage tasks: A translation of research findings into practice (2).
That said, the following is a critical review of three literature papers I was able to find.
Soldier Load Carriage, Injuries, Rehabilitation and Physical Conditioning: An International Approach: 2021 (5)
Type: Secondary source article in a peer-reviewed publication.
Recommendations:
- Load carriage sessions should be performed once every 10-14 days. This recommendation is based upon prior researching suggesting load carriage training be performed every 7-14 days. And secondly, neuromuscular function in the trunk and limbs takes 48-72 hours to recover following a load carriage bout.
- Training programs should include manipulation of load weight, speed, distance, and grade and type of terrain.
- Resistance training should be included within the training program, as well as overall aerobic fitness. Increases in musculoskeletal and aerobic fitness are essential in injury resilience, as lower levels are associated with an increased risk of load-carriage related injury.
- Upper body strength is perhaps more important, as improvements in load carriage performance is more correlated to upper body strength than lower body strength. This recommended is based on a study by Robinson et al: “Aerobic Fitness is of Greater Importance than Strength and Power in the Load Carriage Performance of Specialist Police” (8). The Robinson et al study tested 5km time trials amongst police officers, with 25kg packs. They found the greatest correlation of 5km performance with aerobic conditioning. In terms of strength training, the highest correlations were between 1RM pullups and 1RM bench press, greater than 1RM squat and deadlift (8). 1RM pullups had the greatest correlation, with the authors suggesting that posture maintenance may increase load carriage efficiency (8).
- Immediately following injury, emphasis should be in diagnosis and treatment, with a return to function.
Positive Take Aways and Limitations:
Positives:
- The paper did go through the background of load-carriage related injuries, including common factors increasing injury risk and injury rates.
Limitations:
- Despite the title of the paper, it did not provide any specific recommended strategies in term of injury prevention, nor rehabilitation. Rehabilitation protocols, for example, simply stated early diagnosis and treatment, as well as a sound return to function. These things are obvious to me.
- Simply recommending aerobic and resistance training is completely generalized, with little benefit to a strength and conditioning professional or tactical athlete. In addition, stating that upper body strength is more important did not mention the specific exercises of the Robinson study, I found those from looking at the Robinson study itself. Just stating ‘upper body strength’ could be taken out of context, with athletes doing useless ‘beach body’ exercises, wasting their time. These blanket statements are first, in my opinion, obvious to any competent strength and conditioning coach. And second, could steer practitioners and tactical athletes in the wrong direction, programming useless exercises and rep sequences.
- I was surprised and disappointed that, despite the title of this paper, it is of no real practical value. Reading this, I thought “is that all they have to contribute?” It was as if part of the paper was missing.
Load carriage: minimizing soldier injuries through physical conditioning – a narrative review (6).
Type: Secondary source article in a peer-reviewed publication. This paper summarized research papers and articles, following key search terms related to training and conditioning for load carriage gathered from numerous sources. The sources included original research papers, conference papers, and secondary source articles (journal articles, relevant subject reviews and military reports).
Recommendations (6):
- Combination of resistance training and aerobic training (concurrent training). Studies by Kraemer et al (2001, 2004) suggested that load carriage performance and injury resilience can be improved with concurrent training. Those with lower levels of fitness and exercise will likely make greater initial gains regardless of the type of training, after which specific training is needed to improve performance for a specific task.
- Specificity. The conditioning program must consider the task intensity and requirements. Shorter duration, high intensity to adequately condition the athlete to move under direct fire, for example, and longer durations to adequately develop physical and mental stamina during dismounted patrols, for example.
- Training frequency. Two to four evenly spaced load carriage per month (~7-14 days). However, the authors cautioned that frequency should vary depending upon training intensity (load and speed) and volume (time or distance). They suggest beginning with lighter loads, then progress in weight to match what is required for occupational tasks.
- Recovery. To allow the body to adapt from training stimulus, as well as prevent overload and injury. Inadequate programming of recovery within the training program has been identified as a causal factor in high injury rates among military personnel. This can be achieved by reducing volume throughout long term load carriage training programs. Periodically reducing volume has been shown to drastically reduce injury rates amongst recruits, without negatively affecting fitness. Coined ‘orthopedic holidays,’ strategically placed recovery periods should be long enough for some musculoskeletal recovery, yet short enough to avoid detraining.
- Detraining. Be cautious when prescribing recovery periods to avoid detraining. Lengthy breaks in load carriage conditioning have been shown to increase injury and reduce performance when soldiers resume heavy load carriage training and tasks.
- Conclusion. “A structured and progressive conditioning program with built in recovery periods is recommended.”
Positives:
- The paper did go through the background of load-carriage related injuries, including common factors increasing injury risk and injury rates.
- They at least made some recommendations, addressing the main training factors.
Limitations:
- Again, less generalized than “Solider Load Carriages” paper but was still quite generalized.
- Zero specifics in terms of resistance training.
Resistance Exercise Considerations for Load Carriage (10)
Type: Secondary source.
Recommendations:
- Resistance Training must address three main areas: strength and power development, work tolerance and fatigue resistance, and injury risk mitigation via dynamic trunk stability. Fatigue will set in more quickly without adequate training in these areas, increasing risk of injury.
- Dynamic Trunk Stability. Load carriage results in biomechanical and kinematic changes – increased forward trunk lean, increased hip flexion, and forward positioning of the head and neck – all of which increases injury risk, especially back related injuries. With this in mind, traditional trunk stabilization exercises, such as planks and side bridges, are still valuable, particularly during rehabilitative or when pain is present . However, trunk stability should be focused on dynamic movements. Olympic lifts, squats, and farmer’s walks are some examples by the authors.
- Resistance training at higher load intensities will result in the highest activation of higher threshold motor units, greatest hormonal stimulus, and greatest translation of forces onto the associated muscles, connective tissue, and bone. Higher load training should be in combination of resistance training with moderate loads and shorter rest periods to improve fatigue resistance.
Positives:
- Although recommendations were still more generalized, there was greater specificity, providing useful information that has some practical value.
- The purpose of recommendations was addressed, based on prior research and took into account biomechanics, kinematics, and exercise physiology. This relates to “dynamic correspondence exercises,” exercises that transfer to the tasks, rather than wasting time and energy performing useless exercises.
- The dynamic trunk stability recommendation was solid, in my opinion. As the authors noted, these exercises transfer to a greater ability in handling the load versus doing isolated movements. They did not use the term “core bracing” – but that is commonly how I think of these exercises.
Limitations:
- A few exercises were mentioned. But again, this article does not provide any specifics (ie reps, sets, sample program). They could have included a sample program for one week, and simply provided a caveat.
Conclusion
There appears to be ample research discussing injury rates amongst tactical athletes. However, practical recommendations are lacking, much greater than expected. Further, almost all studies are specific to military soldiers. I have found more studies than the ones mentioned above, but they all essentially say the same thing, providing similar generalized conclusions.
Besides the frequency of load carriage, everything is generalized. The papers did not provide any examples in terms of rehabilitation or resistance training exercises, for example. This was surprising, as you will typically see an example program with other sports such as hockey or football. When I write for the NSCA for example, they always ask for a sample ‘Day 1’ or a sample week program, including specific exercises, reps, sets, rest periods etc. When doing so, I simply include a caveat of it being a sample program only, and that the athlete specific needs, strengths and weaknesses, history, training status etc be addressed. It is like nobody is willing to put their neck out and is simply stating the obvious, using base principles.
That said, anecdotally, I am aware that competent and comprehensive strength and conditioning programs are being implemented, at least amongst the special forces have worked with when preparing for the selection process. This is based upon athletes sharing some of the training they undergo. It is just not being shared amongst the research literature, or even at the TSAC branch of NSCA, at least from what I could find.
As well, physical fitness tests amongst military, firefighters, and police officers are typically based off standard pushups, situps, a run test, and sometimes pullups. Much of this is not specific enough to the actual field, especially when carrying loads under intensive situations. The U.S. Army Physical Fitness Test has shown progress, recently being replaced by the ACFT, with many movements being more applicable to the actual physiological demands. That said, going down this road is a different topic for another article.
Tammy is a professional strength and conditioning coach currently coaching in Arizona as well as an accomplish endurance, obstacle race and fitness athlete.
Want to be a paid, MTI contributor? Email rob@mtntactical.com a current resume and three topic ideas.
References
- Fox, B., Judge, L., Dickin, D., and Wang, H. Biomechanics of military load carriage and resulting musculoskeletal injury: A review. Journal of Orthopedics & Orthopedic Surgeons, 1(1): 6-11, 2020.
- Hauschild, V. Foot marching, load carriage, and injury risk. Technical Information Paper (Army Public Health Center), 12-954-0616. 2016. DOI:10.13140/RG.2.2.25160.52483
- Mala, J., Szivak, T., and Kraemer, W. Improving performance of heavy load carriage during high-intensity combat related tasks. Strength and Conditioning Journal, 37(4): 43-52, 2015.
- Nindl, B. Physical Training Strategies for Military Women’s Performance Optimization in Combat-Centric Occupations. Journal of Strength and Conditioning Research, 29: S101-S106, 2015.
- Orr, R., Pope, R., Lopes, T., Leyk D., Blacker, S., Bustillo-Aguirre, B., and Knapik, J. Soldier load carriages, injuries, rehabilitation and physical conditioning: An international approach. International Journal of Environmental Research and Public Health, 18(8): 4010, 2021.
- Orr, R., Coyle, J., Johnston, V., and Pope R. Load carriage: Minimizing soldier injuries through physical conditioning – a narrative review. Journal of Military and Veterans’ Health, 18(3): 31-38, 2010.
- Orr, R., Coyle, J., Johnston, V., and Pope R. Self-reported load carriage injuries of military soldiers. International Journal of Injury Control and Safety Promotion, 24(2): 1-9. 2016
- Robinson, J., Robers, A., Irving, S., and Orr, R. Aerobic fitness is of greater importance than strength and power in the load carriage performance of specialist police. International Journal of Exercise Science, 1(11): 987-988, 2018.
- Shumway, J. Injury prevention for tactical personnel – Compiling the evidence and lessons learned. TSAC Report, (52)1, 2019.
- Szivak, T. Resistance exercise considerations for load carriage. TSAC Report, (56)1, 2020.