Finding Your Limiting Factor in Running

How to determine what variable is your weakest link in training

Spring training season has officially started, and my Fleet Feet Carrboro/Durham training group kicked off our half and full marathon training plan with one of my favorite workouts: a gear-shifting workout. The gist is a pretty straightforward track workout: you do laps around the track with different speeds. You might split up a lap around the track so that you do different speeds on the same lap or you might do multiple laps at different speeds. Either way you start with a nice easy run, ramp it up to a moderate pace, and then crank it to hard effort. Repeat with recovery shuffles or walk breaks as needed.

The workout:

For a workout that incorporates gear-shifting work on a single lap, your workout might look like this:

In 1 lap (aka 400 meters):

  • 100m of easy effort (40-50% of your max) run
  • 100m of moderate effort (60-70% of your max) run
  • 100m of hard effort (80-90% of your max) run
  • 100m of recovery run/shuffle/walk


For some reason I adore this workout. Maybe it's from all my years of soccer - sprint, walk, jog, repeat for 80 minutes. Maybe it's because I love running fast even if I don't have the stamina for it for long races, but for that short stretch of track I feel like I'm flying. It's like my toes touch that rubber track and I could race even wing-footed Hermes.

The gear-changing workout is all about listening to your body - knowing when to push it and what you need to do to recover. It's knowing your limiting factor.

A little chemistry lesson

A limiting factor is a fairly simple concept that I calculated countless times in chemistry classes throughout high school and college. It's basically your weakest link, or what is consumed first and limits your reaction.

For example, say your chemistry reaction is 2X + 3Y → 1A. To consume all of your X and Y reagents then you need a ratio of 2:3. If we were working in milligrams then you'd (theoretically) consume all of your X and Y reagents with 200mg of X and 300mg of Y to make 100mg of A. But what if you had 200mg of X and only 275mg of Y? Then Y is your limiting factor or limiting reagent - it's used up before all of X is used up, so it limits your reaction and how much of A you produce. Your output is directly affected by how much of Y you have.

Our bodies as a system of variables

Our bodies are essentially a system of variables whose output is our body's overall health and performance. When I prep for a training run I usually think about the variables going into that run to judge my personal performance:

  • Musculoskeletal variables - any performance related to muscle, tendon, bone, or ligament conditions
  • Cardiovascular variables - any performance related to heart or circulatory system
  • Pulmonary variables - any performance related to the lungs
  • Other physical systems variables - any performance related to gut, neurological, immunological, or other systems
  • Mental variables - any performance that is strictly mental and not physical

Of course you could expand this list of variables, but it's a start for checking in and trying to figure out your limiting factor. 

When I first started training for half marathons my limiting factor was fitness - cardiovascular and pulmonary fitness. I simply didn't have these systems built up to support the physical effort that comes with training for a half marathon. Other training cycles my limiting factor was pulmonary - after a couple bouts of nasty pneumonia it was tough to breathe. My leg muscles were ready, my heart was ready, but I just couldn't seem to catch my breath. 

This year my limiting factor is definitely my sore Achilles tendon: it's a slow recovery from that random injury, but at least it's a recovery. But I can't help but wonder if I didn't have this injury, what would be holding me back? Would it just be psychological? And if so, how do I break through that? A half marathon and full marathon can be a daunting thing, and sometimes mental training is the hardest training. Therefore knowing your limiting factor on your runs - whatever that thing is that holds you back from running faster or farther or whatever - is important to know how to train for a successful season.

Do you know your limiting factor when it comes to training, or even other aspects of your life? Let me know in the comments!


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