Marathon Series Part 2: Load Progression

Therapist Patrick Lawrence

If you misses Part 1 of Patrick’s Marathon Series, check it out here!

Every activity we do puts a load on our body. Walking puts a downward load through the spine and legs due to gravity, and leg muscles turn on and off to move us forward. For gardening, a body needs to be able to handle repeated stooping, bending, and kneeling. Muscles in the arm need to be strong enough to grip a weight and bend the elbow against that weight to do a bicep curl. And it is not just muscles that get loaded by an activity—every bone, joint complex, and tissue involved needs to be able to handle the amount of load being placed on it to do the activity without pain or difficulty.

But what actually is load? Here’s a hint: it’s more than just resistance. Load can be divided into three main variables: intensity/resistance, duration, and frequency. When load applies to exercise, it is also referred to as exercise volume (for you science lovers, recall that volume is length x width x height… also 3 elements). So, in an equation:

Load = intensity x duration x frequency

Intensity often refers to the amount of resistance involved, like the weight of the dumbbell being used for a bicep curl. Duration can refer to the number of repetitions or the length of time the activity is being performed. Frequency is how many times the activity is being performed in a period of time, usually measured in the span of a day or a week.

So, when applied to a bicep curl, an example would be 5 pounds (intensity) for 3 sets of 10 repetitions (duration) once a day for 3 days per week (frequency).

Let’s apply it to running. Intensity is not just the speed being ran, but also the elevation. Running uphill at a certain speed is much harder than running on flat terrain at the same speed. There can be several other factors, such has how hard the ground is (sand vs asphalt). Duration is often measured as the length of time or number of miles being run. Frequency is often measured as the number of runs in a week. Thus, running load (or volume) = speed x miles x days/week.

Now, if we wanted to get a number to represent running load, we can break it down further and figure out the physical demand of a marathon. While running, the leg and body must handle 2.5 to 3 times one’s body weight with each step. Multiply that by 180 steps per minute during a 3-hour race, and that brings me to a whopping 9,720,000 pounds placed on my body in the course of one marathon!

The amazing thing about our bodies is that it can adapt to handle these loads. This is where the principle of “progressive loading” comes in. We start with a load a person’s body can handle, and gradually build up the load over a period of time, giving the body time to adapt. It can be easy to see it in running and weight lifting where mileage and weight is gradually increased, but it is crucial in rehabilitation after an injury too. As a therapist, my job is to find a safe load for the painful body/limb/joint, assess the demands of the goal activity being pursued (walking stairs climbing, working, etc) and guide the patient through a plan to get back to that activity pain-free. Frequent monitoring and modifying is needed: increase load by too much too quickly, and the risk of injury increases; increase it by too little, and the body won’t experience enough load to stimulate adaptation. There is a sweet range to keep the load in, and it changes as a person’s body becomes more robust. As therapists, my colleagues and I constantly monitor for signs of over-loading and under-loading, and adjust as needed.

So, with this knowledge, my mantra to myself and my patients is: “slow and steady,” and “patience and persistence.” Or, as one patient told me: “Time plus stubbornness equals success.”

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