The muscles used in cycling: indoors vs outdoors

It’s a well-worn complaint amongst cyclists of all abilities that it’s impossible to put out the same power indoors on the trainer as outside on the road. In one study published in the Journal of Strength and Research, moderately trained cyclists were asked to ride 40 km at a fast pace, both indoors and outdoors, without knowing their speed or heart rate. The subjects almost unanimously delivered less power indoors. 

So, if you do find it harder to lay down the power indoors, you’re far from alone. In fact, you’re in the overwhelming majority. A range of explanations are offered for this phenomenon: from cooling and ventilation to the constant distraction of the road flying by. They may play their part but, in this article, we dive deeper and look at the muscles used in indoor and outdoor cycling and ask whether that could explain why it’s just so difficult to drop those watt bombs indoors.  

On the surface, indoor cycling and outdoor cycling are incredibly similar. They both engage and train the cardiovascular system in a comparable way and to roughly the same extent. However, where they differ is in the pedaling dynamics and muscle engagement required by each mode. Understanding these differences could help you optimize your training for better performance and injury prevention.

Muscles engaged in cycling

Obviously, cycling predominantly works the lower body muscles, with significant engagement of the core and, to a lesser extent, the upper body. 

  1. The quadriceps are the primary movers during the pedal stroke, especially during the downstroke (push phase). They extend the knee and provide the bulk of the power.
  2. Hamstrings are crucial during the upstroke of the pedal cycle (pull phase). They work to flex the knee and help lift the pedal.
  3. The glutes are heavily engaged during the downstroke, providing power and stability.
  4. Calves (the gastrocnemius and soleus) assist in the push-off phase and help stabilize the ankle.
  5. The iliopsoas and other hip flexors are essential for lifting the pedal during the upstroke.
  6. A strong core is vital for maintaining proper posture and balance, especially during long rides.
  7. While not as heavily engaged as the lower body, muscles in the shoulders, arms, and back help maintain stability and handle the bike.

How indoor differs from outdoors

Another study published in the Journal of Applied Biomechanics asked riders to cycle at certain intensities both indoors and outdoors. Unsurprisingly, subjects consistently reported that the effort felt significantly more strenuous riding indoors. However, researchers also discovered that the cyclists’ force profiles differed significantly riding indoors compared to riding outdoors. How could that be?

Outdoors: The dynamics of outdoor cycling, including the momentum and natural resistance provided by the terrain and environment, can result in a more fluid pedal stroke. When you ride outdoors you activate your muscles in a very distinct pattern as shown on the left force circles in the image below. Most of your power is put in through the big muscles in your legs: your glutes first, and then your quadriceps. These are very big and strong since you constantly use them for standing, walking and running.

Indoors: Current indoor trainers use a flywheel to represent the inertia of your body (and bike) weight that you experience outdoors. In reality, flywheels are usually a factor of 10-20 too light, resulting in pedal forces that look much more like the force circles on the right. Little force can be put into the lightweight flywheel because it accelerates quickly as you start pushing. This is the whining sound you hear with every push: the speed of the flywheel increases. As a result your glutes and quads cannot push as hard as they want which leads to a higher perceived exertion and more sustained muscle engagement, particularly the hamstring. 

In addition to pedaling dynamics, the varying terrain, road surface and wind resistance you encounter riding outdoors will subtly shift which muscles are being used and the extent to which they’re being used at any given time. These constant adjustments also require you to engage your core muscles and upper body more than riding indoors.

How to train indoors to maximize success outdoors

In light of all this, it’s little wonder that studies suggest that, while both indoor and outdoor cycling provide substantial cardiovascular benefits, the varied resistance and dynamic conditions of outdoor cycling might offer superior muscle engagement and endurance benefits.

So, should we only ever train outside? Obviously, that’s not practical for most of us – for reasons of family, work, time, weather or road conditions. Happily, you can tweak your indoor training to better imitate outdoor cycling and more accurately engage the muscles used riding outdoors. In short, you can train with more specificity.

  1. Get a TrueBike or TrueTrainer. OK, we were bound to say this, right? But the TrueBike and TrueTrainer are the only smart bikes and smart trainers available that use a motor and robotics instead of the flywheel. They create a realistic riding experience and engage the leg muscles in the same way as riding outside. Learn more here.
  2. Alter the torque and cadence regularly to simulate changing terrain and make micro adjustments to the muscles being recruited.
  3. Doing regular high intensity intervals and sprints on the smart bike or smart trainer will help you strengthen those all-important core muscles you use to balance outside.

Both indoor and outdoor cycling offer unique benefits and challenges. While the primary muscles engaged remain consistent, the differences in muscle utilization, especially in the pedal stroke dynamics, can significantly impact your training and performance. 

By understanding the muscle dynamics of both indoor and outdoor cycling, you can create a balanced training plan that enhances strength, endurance, and overall cycling efficiency and decide whether your current indoor bike or trainer needs upgrading to a TrueBike! 

But this is really only half the story. Next week, we’ll look at the role that neural programming plays in cycling and how you can use your brain to become a better cyclist.