Stress Fracture and Injury Risk to Military Recruits

Written by Ben Bunting: BA, PGCert. (Sport & Exercise Nutrition) // British Army Physical Training Instructor // S&C Coach.


When personnel enter the military they are put through an intense regime that changes them from a civilian in to a professional soldier. 

This includes lots of physical training that may include load carriage, long distance running, gym work and marching. 

Needless to say, if a person is not prepared or conditioned it could result in injury or illness. 

This article takes a look at the risks to military recruits when going through their initial training.

Soldiers and Energy Intake

A recent study showed that soldiers who took an extra 1,218 kcal per day during a British Army combat course maintained circulating leukocyte counts and increased salivary immunoglobulin A secretion which is important for the immune system. 

Evidence of energy deficiency among military personnel is based on lab studies and cross-sectional comparisons of male and female athletes. However, longitudinal prospective studies of military populations may yield more definitive results. Although military field studies are not specifically designed to assess energy availability, they typically include subjects exposed to multiple stressors such as fatigue, low-calorie diet, and rigorous physical training.

One such study that monitored energy intake among international military forces all reported that recruits were likely to be underconsuming energy with a lack of carbohydrates compared to other macronutrients. It also reported a significant jump in push up performance when protein intake was increased. 

Does Energy Deficiency Increase Injury Risk?

Relative energy deficiency (RED) is an issue for athletes in all sports. A deficiency in energy intake can have a dramatic impact on performance and health. Low energy stores can make it difficult for athletes to recover after rigorous training. If they push themselves too hard without adequate recovery, they may suffer serious musculoskeletal injuries. Furthermore, we should start to consider soldiers as athetes based on their activity levels, plus the stresses they experience under training conditions.

In recent research, a lack of energy intake has been linked to increased cardiovascular disease in male athletes, but the exact mechanisms are not known. Insufficient energy intake may also increase the risk of gastrointestinal problems, bodily aches and head aches.

Another common symptom of energy deficiency in athletes is decreased muscle strength and endurance. Energy deficiency can negatively affect a person's coordination and concentration. This lack of calorie consumption can also affect a person's endocrine and metabolic functions. Low energy intake can also compromise a person's immune system, which could cause a host of medical problems.

Relative energy deficiency in sport (RED-S)

Low Energy Availability (LEA) increases the risk of bone stress injuries, which can lead to recurrent injuries in athletes. The condition also causes chronic fatigue, underperformance, and psychological problems. Therefore, athletes must make sure that they consume adequate calories during training and follow a proper nutrition plan. Their nutrition plans should be monitored regularly and adjusted if necessary based on performance and activity levels.

Another sign of low energy availability in female athletes is irregular menstruation. Female athletes with irregular menstrual cycles have been linked with lower bone mineral density (BMD) and reduced bone strength, which increase their risk of bone stress injuries. The absence of menstruation, inadequate energy and nutrient consumption couples with reduced bone mineral density is referred to as the 'Female Athlete Triad'.

Despite being a common symptom of relative energy deficiency in sport (RED-S), it can be difficult to diagnose in athletes, particularly self-diagnosis. It is important to consult a sports nutritionist if you are experiencing any of these symptoms. If you do not have access to one, your military medical team may be able to assist or your physical training instructor.

By increasing their energy intake, athletes can reduce the time it takes to recover from an injury. The key is to ensure that the body receives adequate carbohydrates and adequate protein.

What is a Stress Fracture?

A stress fracture is a type of bone injury that occurs when a person experiences repetitive stress. It's important to know the symptoms, causes, and treatment options for stress fractures. Treatment for these injuries should be coordinated with a multidisciplinary approach. X-rays are one of the standard tests for diagnosis. However, in some cases, a stress fracture might not be immediately apparent on an X-ray. In this case, bone scans, CT scans, or MRIs may be necessary. These tests usually produce immediate results and can help determine whether a stress fracture has developed in a person's bone.

Often, stress fractures occur in the upper body, affecting the ribs and wrists. They can also develop in the arm or leg bones, especially in individuals with reduced bone density. Elderly people are at risk because they tend to lose their appetite and don't consume enough protein or exercise as much meaning they often fall and can become injured. Soldiers are also susceptible to stress fractures in the lower limbs due to heavy loads being carried over undulating terrain. 

Women are especially at risk for stress fractures due to the female athlete triad. Additionally, lack of calcium and vitamin D can lead to weaker bones and muscles among all members of society.

Stress Fractures in Military Recruits

The 2022 study published in the International Journal of Environmental Research and Publih Health study analyzed medical records of military recruits and coded them according to ICD-9 or ICD-10 codes. It identified fatigue fractures and stress fractures. Each visit was reviewed, and radiographs were obtained in all but one case. In addition to plain radiographs, scintigraphy and magnetic resonance imaging were performed to confirm a stress fracture diagnosis. Both modalities were consistent over the study's duration.

The study also identified risk factors for stress fractures. It found that those who sustained a stress fracture during basic military training were four times more likely to be discharged. These injuries also result in higher work days lost due to injuries, increasing the financial burden for the military. The findings indicate that training regimens should be revised to reduce the likelihood of stress bone injuries.

Studies also reveal that the adaptation of bone formation can be optimized through a range of training and nutritional strategies. This can lead to a stronger, more resilient skeleton and protect recruits from stress fractures during their service. However, more evidence is required to determine if these treatments are effective in reducing the risk of stress fractures in military recruits.

Strength and Conditioning

Although age and gender are not modifiable factors, a recruit's fitness levels and weakness can be addressed early in training. Training strategies through a structured training program can help prevent stress fractures. The authors recommend that all military recruits start an injury prevention program at the start of their training. This program should be mandatory, but should not be limited to recruits with risk factors.

Moreover, the type of military training has a profound impact on the risk of stress fractures. For instance, the Royal Marines of the United Kingdom undergo a gradual increase in mileage during their first few weeks, which allows the body to undergo remodeling processes. Then, when recruits progress from infantry training to commando training, their mileage suddenly increases.

Observations of the recruits from the USMC also found that those who reported prior regular physical activity were less likely to suffer from bone fatigue fractures, whereas those that had fractures reported no prior training. Regular physical activity is essential in preventing stress fractures. The authors recommend that recruits seek medical advice when they experience musculoskeletal pain and consider these risks when planning their physical training programs. 


This study showed that military recruits who have multiple metatarsal stress fractures were likely to require 12 to 14 weeks of rehabilitation, whereas those with single metatarsal fractures took up to 21.1 weeks. These stress fractures are also responsible for the majority of the time that recruits undergo rehabilitation.

While stress fractures are caused by repetitive, cumulative micro trauma to bone, they are a growing concern. Increasing rates of this type of fractures may increase morbidity, lead to long absences from training, and result in substantial economic losses. For this reason, the study sought to estimate the incidence and distribution of stress fractures in Border Security Force cadets in Bangalore.

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Gender Differences in Muscle and Bone Susceptibility Factors

Men and women differ in their response to health conditions and treatments. Women are more likely to suffer from osteoporosis, a condition that causes brittle bones and puts individuals at risk of fracture. For instance, more than a third of women over the age of 50 in Australia are diagnosed with osteoporosis, compared with 6% of men.

The differences between men and women in their bone and muscle mass are most apparent during puberty. Boys' peak bone mass is higher than that of women, while men's bone growth rate is slower. The latter is due to hormonal differences that limit bone growth. Women's peak bone mass is lower than that of men, and is a function of estrogen levels.

Men had greater bone area in the tibia and femur, and greater bone mineral density (BMD) and bone mineral content (BMC) at the hip. In contrast, females had a smaller femur and tibia. Additionally, males had more cortical thickness in their tibia and greater tibia BMD. Nevertheless, these differences were not significant.

As women have a smaller bone mass than men, they are more susceptible to bone injuries, including stress fractures and breaks. Because of this, female athletes should pay special attention to bone health. This includes proper nutrition and core strengthening. Furthermore, women should also structure their exercise routines to help minimize the risk of bone injuries.

Gender differences in muscle and bone susceptibilities have been studied in collegiate athletes. A study by Huston and Wojtys examined 100 female and male athletes. The researchers observed significant differences in muscle response times. In particular, female athletes had slower peak knee flexion torques, while male athletes experienced faster peak knee extension torques. Female athletes were also slower in the hamstring than their male counterparts.

How Common Are Stress Fractures in the Military?

Stress fractures occur more frequently in men than in women, according to a 2014 study in the US Army. This study focuses on the frequency of stress fractures in the lower extremities, and the cause of them. The researchers also determined whether trauma to the body is more likely to lead to stress fractures than in the general population.

While stress fractures can develop at any time during combat training, the majority of these injuries occur during the first two to three weeks of training. However, these injuries can also occur later in the military career. Although the number of stress fractures decreased with time, their incidence persisted into the sixth month of service.

The incidence of (stress fractures) SF was higher in the initial training period, and reached its highest point at about 12 weeks. The majority of SFs were treated conservatively, with only eight fractures requiring surgical treatment. However, early detection and treatment of SFs can help in early recovery and early return to full activity.

Stress fractures are common overuse injuries. They typically affect the lower extremities, but have also been reported in the upper body and in the ribs. The most common bones affected are the tibia, fibula, and metatarsals. Less commonly, they occur in the pelvis and femur.

Stress fractures occur when the body cannot heal itself quickly enough to heal the damage caused by physical activities. According to a new military report, recruits experience stress fractures 18 times more often than non-recruits, and a study from 2014 recorded a 2.4% stress fracture rate among recruits. 

A study of Israeli recruits saw a 31% incidence of stress fractures with 80% of the fractures being located in the tibial or femoral shaft.

One study of Indian recruits saw that the average age of injured recruits was 20 and the most common sites of fractures were seen in the tibia tibia (52.11%), fibula (23.59%), femur shaft (9.50%), femur neck (7.74%)and metatarsals (7.04%). 

What happens if you get a stress fracture in basic training?

In such cases, the injured soldier will seek medical treatment. While this may cause a delay in training, the US military will provide health care during the recovery process. In some cases, the patient may not be able to return to his or her original platoon but be moved to a different class. The injured soldier may need weeks to recover with a report published in the Military Medicine journal stating it could take up to 62 days.

This study reported an average recovery time of 5 weeks with a full return to activity within 18 weeks.

According to various studes, stress fractures tend to occur during the first six weeks of service and during unit physical training. The study found that the stress fracture rate increased gradually over these eight weeks. The increased workloads may result in an increased risk of stress fractures.

Nutrients Required For Military Training

If you are a member of the armed forces, you should know that you need to include certain nutrients in your diet to help you prepare for military training. For example, you need to consume a certain amount of carbohydrates each day to keep you energy and mood-stable, as well as a certain amount of protein and healthy fats. While the military provides meals, you need to choose the right kinds of foods to make sure that you get the nutrients your body needs.

A typical recruit needs to consume about 3,250 calories a day. However, there are some circumstances where this may need to be higher. For example, military personnel who train for long periods may such as the Royal Marines require 4200 calories a day. The amount of food that a typical service soldier needs is higher if they are part of a special forces unit.

In addition to vitamins and minerals, optimal nutritional status is critical for a Soldier's health and performance. Research has shown that specific micronutrients can influence their physical performance. For example, iron deficiency can impair a soldier's ability to process oxygen if their red blood cell count isn't optimal. Another example is calcium, which is essential for bone health. Moreover, intense physical activity can increase the release of parathyroid hormone, which regulates calcium metabolism.

Despite the importance of a balanced diet for a soldier, dietary intake of vitamin D, calcium, and iron has been found to be low in British Army recruits. Compared to modified dietary variety score (MDRVs), British Army recruits consume only half the recommended daily intake of these nutrients, which is not optimal for their overall health. It is important to consider this as an opportunity to improve the outcomes of military training.

The British Army's standard Phase One training consists of a variety of physical exercises, military-specific skills training, and field exercises. These types of training involve large amounts of energy expenditure, daily training loads, and high risk of injuries. Inadequate dietary intake of these nutrients can negatively impact mood, physical performance, and musculoskeletal injury.

While the recommended protein intake for endurance athletes is 1.6-1.8 g/kg/d, military training requires higher intakes. This is because military training is more strenuous than endurance training, which stimulates muscle protein synthesis at a much higher rate. These higher protein intakes are important for a military trainee to remain fit and healthy and recover after intense training.

In addition, military training requires soldiers to meet rigorous standards for competence and efficiency. Consequently, the nutritional requirements of an special operations forces (SOF) soldier are high and his baseline healthy eating index (HEI) score is high. Thus, the dietary patterns for SOF Soldiers must be optimal for this level of physical training. They also need to meet rigorous assessment requirements during training exercises.

General daily macronutrient recommendations for people engaged in high to very high activity levels:

  • Carbohydrates: 6-12 grams per kg of bodyweight
  • Protein: 1.2-2 grams per kg of bodyweight
  • Fats: No less than 20% of total calorie intake

Calories Required For Combat Soldiers

The military has a complex dietary plan for combat soldiers that includes more calories than the average American. This diet is meant to provide soldiers with the essential nutrients they need to stay active and alert during intense combat. The calorie intake needs for soldiers vary according to their lean body mass. Those with high lean body mass require more calories per day than smaller individuals.

The military recommended daily allowances (MRDA) is meant to be used by professional military personnel for menu planning, dietary evaluation, and food research and development. These dietary guidelines are based on estimates of nutritional requirements for healthy military personnel. In addition, these guidelines are intended to be an essential basic tool in nutrition education. Therefore, it is important to follow these guidelines carefully to ensure that military personnel are receiving the proper nutrients.

Insufficient calories and essential nutrients have been known to cause the body to malfunction. Nutritionists in the U.S. erred on the side of caution and set minimum nutrient requirements for soldiers that were 30% higher than the average American. 

As we have seen the Royal Marines require over 4000 calories per day during their intial 32 week training period and similar requirements have been published for those who enrol the intial 14 week infantry basic training within the British Army.

Important Micronutrients For Physical Training

Various vitamins, minerals, and other micronutrients are necessary for optimal fitness and performance. They help to protect the body against exercise-induced oxidative stress and promote recovery after long workouts. Some of the most important micronutrients for athletes include vitamin C, vitamin D, and folic acid.

These vitamins and minerals are essential for the body's energy metabolism. In addition, they promote muscle recovery and delay fatigue during workouts. In addition to regulating energy metabolism, they also improve the body's ability to use free fatty acids and glycogen. Vitamin C increases absorption of iron, whereas vitamin D increases the metabolism of calcium.

Vitamin D is obtained from sunlight and is stored in the body. Plants cannot absorb vitamin D, so the best sources of vitamin D are meat and fortified foods. Inadequate vitamin D intake is associated with higher risk of upper respiratory infections, which can be particularly harmful for endurance and high intensity athletes.

Other important micronutrients for physical training include zinc and magnesium. These minerals are essential for muscle repair and energy metabolism and are vital for immune health. However, too much zinc and magnesium can cause adverse effects. As a result, athletes should make sure to consume the recommended amounts. Vitamins C and E should be consumed in appropriate amounts to support optimal health and performance.

Vitamin B is another important micronutrient for athletes. It is necessary for optimal bone health and reduces the risk of osteoporosis and arthritis. It also ensures that the joints are lubricated, which is essential for optimum joint function. These nutrients are vital for promoting bone health during physical training.

Iron is a trace mineral that plays a vital role in energy production. A deficiency can lead to weakness and fatigue. Moreover, inadequate iron intake can result in the breakdown of iron-related enzymes in the body, which affects energy production. Iron is an important ingredient in hemoglobin and myoglobin, which carry oxygen to the cells.

Magnesium is also important for physical activity. It helps to prevent cramps and improves muscle recovery. It is part of over 300 enzymes in the energy metabolism of the body and also helps form bones. It improves bone density, which protects against stress fractures. But it can be easily lost during strenuous activity, so it is important to eat foods rich in magnesium before hard workouts.

However, knowledge of the required nutrients seems to be lacking amongst recruits, this study of British Army recruits demonstrated a lack of nutritional knowledge. The concluding remarks advised improved nutritional intervention to optimise career behavior


Stress fractures and injuries are a risk to all military recruits. This can be due to a number of factors such as prior sport participation, training methods, lack of recovery and low energy intake coupled with inadequate macroand micronutrient intake. 

Some militaries report very high incidences of injury relating to the lower limbs that can take up to 18 weeks of rehabilitation.

However, injury risk can be prevented with improved training and nutritional strategies as well as educating soldiers to make better and more informed choices. 


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