Issue #30: Why Your Calves are Your Distance Engine

🧃 1st Phorm Phormula-1 Clear

📈 Training Update – Building fitness back up

These last few weeks I have been really pushing training volume, primarily through more mileage but also in cross training (bike, row, ski). Training load is something I think about pretty often when I’m planning out my workouts for the week or the current cycle. More time doesn’t always mean more stress on the body → a 45 min intense session is likely more stress than a 75 min easy bike ride for example.

Having metrics besides just “total time” or “total mileage” is important to me because I want to ensure I’m going through phases where I am progressively stressing the body a little but more over time. This chart below is from my coros dashboard and something I regularly check in on. The green line is my base fitness, which is more of a long term view (how much work have you done in the last 42 days). The blue line is how much work you have done in the last 7 days, so more of a “what have you done for me lately” metric.

In a season with many races, it’s nearly impossible to make the green line just keep going up all the time. Tapering for races puts a dent in training progress. I had a long offseason of fitness building (steady increase in the green line), a two-part racing block in the fall (down, then up, then back down), and now it’s almost like I’m right back into an offseason of fitness building. The goal is to get this green line as high as possible about 10 days before HYROX World Championships in June, with a couple sharp drop-offs along the way in January (Phoenix Elite 15 doubles major) and March (DC North American regional Elite 15).

An important reminder: Fitness builds over time. Crushing one workout doesn’t mean that much, but doing it twice a week for 50 straight weeks matters a lot.

🏃 Muscular strategy shift in human running

This paper, "Muscular strategy shift in human running: dependence of running speed on hip and ankle muscle performance" by Dorn et al. (2012), provides critical insights for runners by identifying a specific "crossover point" in how our muscles produce speed → full text paper.

The study used musculoskeletal modeling to determine how individual muscles contribute to running at speeds ranging from a slow jog to a maximal sprint. Here is a summary of the findings and their practical importance to us.

The Core Finding: The "7.0 m/s" Threshold

The researchers found that humans use two distinct muscular strategies to increase speed, and the transition happens at approximately 7.0 meters per second (around a 3:50 minute/mile pace or 15.6 mph).

1. Speeds < 7.0 m/s (Distance Running Range): Speed is primarily increased by increasing stride length. This is driven by the ankle plantar-flexors (soleus and gastrocnemius). These muscles provide the vertical support and "push-off" force needed to propel the body forward.

2. Speeds > 7.0 m/s (Sprinting Range): The ankle muscles reach a physical limit → they cannot contract fast enough to provide more force as ground contact time shrinks. To go faster, the body shifts strategy to increase stride frequency. This is driven by the hip muscles (iliopsoas, gluteus maximus, and hamstrings), which work harder to swing the legs through the air more rapidly.

Importance to us

For probably every single person reading this, race paces, or even any pace we’re running in a workout, are way slower than 3:50/mile.

This means that… the role of the calf is critical! Both the Soleus and Gastrocnemius. For people focused on in improvements in the 5k distance and above, the calves are our speed engines.

• Performance: Improvements in your 5k or marathon time at these paces come from increasing your stride length via better force production in the stance phase (foot on the ground).

• Training Tip: Strengthening the soleus is paramount. The study highlights that the soleus provides the bulk of vertical support. Heavy calf raises (seated for soleus, standing for gastrocnemius) can improve the force-generating capacity needed to maintain a longer stride over long distances.

And while you’re here, check out this cool chart on IG that shows the differences in muscles used at these two drastically different paces.

📈 Work with the Threshold Lab