You jump on the trainer, lock into a sweet spot session, and suddenly those target numbers feel like grinding through wet cement. Yet out on the open road, that exact same wattage feels fluid, natural and completely manageable.
If you find it harder to lay down power indoors, you're far from alone. In fact, you're in the overwhelming majority.
In one study published in the Journal of Strength and Conditioning Research, moderately trained cyclists were asked to ride a 40 km time trial at a fast pace both indoors and outdoors without seeing their speed or heart rate. The results were clear: subjects almost unanimously produced less power indoors.
People often blame poor airflow, overheating or the sheer boredom of staring at a wall. While those factors play a role, the real answer lies much deeper in your physiology.
The way your muscles fire changes significantly when you step off the tarmac and onto a turbo trainer.
Muscles engaged in cycling: the basics
On the surface, indoor and outdoor riding look identical. Both engage your cardiovascular system in the exact same way. However, pedalling dynamics and muscle recruitment profiles tell a completely different story.
To understand why indoor riding feels harder, let me first break down the primary muscles involved in a pedal stroke:
- Quadriceps: The main power generators during the downstroke (push phase) as they extend your knee.
- Glutes: Heavily recruited alongside your quads to drive power and stabilise your pelvis during the downstroke.
- Hamstrings: Essential during the upstroke (pull phase) to flex the knee and lift the pedal through the bottom of the stroke.
- Calves (gastrocnemius and soleus): Assist in the push-off phase and stabilise your ankle joint.
- Hip flexors: Pull the pedal back up during the recovery phase of the stroke.
- Core and upper body: Stabilise your torso, maintain posture and transfer force from your lower body into the pedals.
Why indoor pedalling physics hit differently
A separate study published in the Journal of Applied Biomechanics asked cyclists to ride at identical power outputs both indoors and outdoors. Unsurprisingly, riders reported that indoor efforts felt significantly more exhausting.
When researchers looked at the force profiles, they found something fascinating: the pattern of force application across the pedal stroke was drastically different.
Outdoors, real-world momentum, wind resistance and micro-adjustments in terrain create a natural flywheel effect. As you push down, you activate your largest, strongest muscles – your glutes and quads – in a smooth, powerful arc. These big muscle groups are built for heavy lifting because you use them constantly for walking, running and standing.
Indoors, standard smart trainers use a metal flywheel to simulate that outdoor inertia. The problem is that most physical flywheels are simply too light to replicate your real-world body and bike weight.
Because the flywheel accelerates rapidly the instant you apply force, pedal resistance drops off unnaturally at the peak of your downstroke. Your glutes and quads can't push as hard as they want to, forcing your hamstrings, hip flexors and stabilizing muscles to work far longer through the stroke to keep the flywheel spinning.
That shift in muscle recruitment pattern creates higher perceived exertion, quicker localized muscle fatigue and a frustrating drop in overall power.
How to train indoors to maximise outdoor speed
Does this mean indoor training is a waste of time? Absolutely not. For busy age-group athletes juggling work, family and life, the indoor trainer remains one of the single most efficient tools in your arsenal for getting maximum bang for your buck.
You just need to train smarter to bridge the gap between the pain cave and the road:
- Vary your cadence and torque: Don't just sit at 90 rpm for an entire workout. Mix low-cadence torque work (60 – 70 rpm) with high-cadence spinning (100+ rpm) to train your neuromuscular system across different force profiles.
- Focus on core stability: Without the natural tilt and sway of an outdoor bike, your core works differently indoors. Incorporating targeted off-bike strength work ensures your stabilisers don't fail when you transition back to the road.
- Use high-intensity intervals strategically: Hard, short bursts force motor unit recruitment across all muscle groups, helping bridge the gap between indoor mechanics and outdoor power output.
Stop guessing, start performing
Indoor and outdoor cycling both build a massive aerobic engine, but understanding the difference in muscle dynamics allows you to structure your training with real intent. When you fuel properly, target the right energy systems and respect how your muscles fire on the trainer, every indoor watt translates into real-world speed.
Tired of generic turbo plans that leave you feeling broken without making you faster on race day? Come say hi to the TricoachMatt coaching family. I build smart, personalised endurance coaching around your real life so you can perform at your best, stay healthy and actually enjoy the journey.
