This article by Dr. Ian Nurse originally appeared in the Sept/Oct 2014 issue of our magazine. 

Over the past few years we have examined a wide spectrum of running related injuries ranging from iron deficiency anemia to IT band syndrome. This month, I want to examine why injury occurs in the first place by exploring the idea of load vs. capacity, a concept that was introduced to me by my mentor, Dr. Grace Steinley. It’s easy as runners to attribute any injury we suffer solely to mistakes we made in our training: too many miles, racing too often, too many hill repeats, not enough rest days, wearing the wrong shoes. In reality, injury occurs due to many factors beyond training regimen when there is an imbalance between load and capacity. What does that exactly mean? This article will try to explain.

First, let’s start with load. Every day we are placing stress on our body both in terms of training and the everyday challenges of life. This is the load.  Injury occurs if the load is greater than capacity. Injury prevention thus means decreasing your load or increasing your capacity.

Examples of load as explored by Dr. Steinley:

Exercise.  The health benefits of exercise outweigh the negative effects of load as long as the intensity (how hard you exercise), frequency (how often you exercise), and duration (how long you exercise) are managed.  For example, exercising seven days a week at high intensity for several hours will quickly overload the body’s ability to recover resulting in injury. Bear in mind that not every body is created equal. Some people will need to modify their schedules to prevent injury.

Job Duties.  Sustained or repeated postures load particular structures in the body.  You will become injured if the load exceeds the structure’s capacity.   For example, repeated cradling of a phone on one shoulder may lead to headaches or damage in the muscles and/or discs in the neck.

 Weight.  Additional weight to carry around means additional load on the body’s joints, bones and soft tissue (muscles, ligaments, tendons and fascia)

Training Errors. Worn out shoes increase the load on your body.  Running on concrete vs. a dirt trail adds to excess load on your body.  Running only on one side of a cambered road unevenly distributes the load to your body.  Running with biomechanical problems and muscle imbalances increase load, and, unfortunately, are difficult to discover before an injury occurs without professional help. Sporadic training (i.e. skipping weekday runs and only completing long runs or vice versa) doesn’t allow the body to adapt to the stresses and leads to injury.

Now, let’s explore capacity which is your body’s ability to recover.  Injury is prevented if capacity is greater than load. Injury prevention means increasing your capacity:

 Fitness.  Increasing overall fitness increases the body’s capacity to withstand load.

 Strength.  Similar to fitness, by increasing strength, your body is more equipped to handle the load you place on it.  For example, by having strong stability muscles in the deep neck you will be at less risk for postural related overuse injuries, such as headaches. As a runner, your endurance will continue to grow, but this actually leads to a decrease in muscle strength. This needs to be counteracted to prevent injury.

Muscle Balance.  Not only is it important to be strong, but to have the proper balance of strength.  Next to producing movement, a muscle’s largest job is to stabilize joints.  To effectively do this, a proper strength ratio is required of all muscles around a particular joint.  If your muscle isn’t doing the job it’s supposed to do, the joint will sustain injured.

Nutrition. Food provides your body building blocks for energy and muscle repair.   If what you put into your body is lousy, the repair and energy you receive will be lousy as in return. Eat high quality carbohydrates, proteins, and fats.

 Sleep.  Fact: a sleep-deprived person doesn’t heal as well as someone who’s well rested.  Sleep deprivation creates a hormonal imbalance which delays or even prevents recovery.

 Stress.  What’s going on in your life beyond training can greatly affect your capacity and therefore increase your risk for injury. Work, family, and friendship responsibilities can take a physical and mental toll causing a similar hormonal imbalance that again causes a delay or even prevents tissue repair and recovery.

As you can see, several factors go into keeping the balance between load and capacity and staying injury free. If you find yourself stuck in the injury cycle, it might be worthwhile to put your training log aside and start examining your own load vs. capacity to see if an imbalance may reside. If so, adjust according and keep on running!

Dr. Ian Nurse has recently started his own sports chiropractic practice, Wellness in Motion Boston. More information can be found at www.wellnessinmotionboston.com.

If you would like to read more from the Sept/Oct 2014 issue, click here.