Spinning Classes: What Indoor Cycling Really Gives You

Spinning is the training stimulus almost everyone has met and almost nobody can place. One hour of music, sweat and instructions — but how much of it is training and how much is just effect? The short answer: a well-ridden class is a solid threshold and base stimulus, a workable cross-training session and an acceptable substitute for an easy ride. It is not a run, not a substitute for volume, and not a measuring instrument.

What spinning is — and what it is not

Spinning, indoor cycling, RPM, Les Mills Cycle: the same format behind different names. Forty-five to sixty minutes on a fixed bike with a heavy flywheel, guided by music and instructions, with changing positions (seated, standing, in the drops) and changing resistance. The decisive difference from a smart trainer: you do not control intensity through a watt target but through resistance and cadence — and you are being led from outside.

That is the real value of the format. Anyone who cannot face prescribing themselves a structured session after a long working day gets fifty minutes of work handed to them here, without having to make decisions. But that is also its weakness: the class does not know your training plan. It does not know you have a 28-kilometre run on Saturday, and it will not take any account of it.

The stimulus: what a class actually sets

A typical 60-minute class sits between 75 and 85 percent of maximum heart rate for long stretches, with several short excursions above it. Expressed as training load that is roughly 50 to 80 TSS — about what an hour of easy riding with a few tempo efforts costs. Energy expenditure realistically lands at 450 to 700 kilocalories, depending on body weight and actual power.

What matters is the distribution. Many class formats use interval blocks of 30 seconds to four minutes. That hits an area endurance athletes often neglect: the threshold. Anyone who only runs easy and does one interval session a week picks up a second usable stimulus here — though without the precision of a planned session.

• Base share: The warm-up and cool-down phases are usually too short to build real aerobic base. Ten to fifteen minutes inside a class is no substitute for 90 minutes of easy riding.
• Threshold share: This is where the strongest benefit sits. The intervals are long enough to provoke lactate production and short enough not to overload.
• Neuromuscular share: High cadences (110–130 rpm) and surges out of the saddle train coordination and strength endurance — things an ergometer session often lacks.
• Missing share: Long-duration load. No class lasts three hours, and that is exactly where marathon and gran fondo are decided.

The instructions: what to take and what to ignore

Class instructions are written for a mixed group, not for you. That is not a flaw of the format, it is its logic — but it means you have to listen selectively. Three patterns recur almost everywhere:

• "Resistance up, stand up now!" Sensible in moderation, but too frequent in most classes. Too many standing phases at high resistance push cadence below 60 rpm and load the knee. If you have knee issues: stay seated and back the resistance off slightly.
• "Fast, faster, faster!" High cadences are valuable — but only with clean technique. The moment you start bouncing in the saddle, the cadence is too high. Bouncing is a technique fault, not an achievement.
• "Thirty seconds left, give it everything!" Good for the stimulus, expensive for recovery. Three of those sprints in the final quarter mean two days of elevated fatigue — and if a key session is scheduled the next day, that was a bad trade.

The practical handling: ride the class, but steer by your own plan. If your plan calls for an easy day, keep the resistance low and the heart rate in zone 2 — even while the group sprints. That is not weakness, it is the only way to integrate a group format into an individual plan.

Spinning in the training plan: four concrete use cases

There are four situations where a spin class is more than killing time. In every other case a smart trainer is the better choice, because you can hold intensity exactly.

• Winter base with structure. November to February, two 60-minute classes per week plus one long ride at the weekend. The class supplies the intensity that is hard to dose outdoors in the cold and dark. How that fits into total volume is covered in indoor trainer training.
• Cross-training during running injuries. With a bone stress injury, stress fracture or plantar fasciitis, spinning is one of the few loads that challenges the cardiovascular system without loading the foot. Important: no standing, low resistance, high cadence — and clearance from your doctor.
• Second session on a double day. Anyone running 80 to 100 kilometres a week can ride the second session of a double day as 40 minutes on the trainer. A full class with music is too hard for that; the first 40 minutes of a class work well.
• Triathlon bike training indoors. For Olympic distance, a 60-minute class with two blocks at target intensity is genuinely race-like. For long distance the duration is simply missing. How those bike legs are built is covered under triathlon training.

Sample week: 45 running kilometres plus two classes

A realistic week for someone holding 45 running kilometres through the winter while spinning twice a week. The class replaces the second quality session, it does not come on top of it:

• Monday: Rest day or 30 min mobility.
• Tuesday: 60 min spinning, moderate resistance, two 8-minute blocks at threshold. About 65 TSS.
• Wednesday: 10 km easy run, zone 2.
• Thursday: 8 km with 5 × 3 min at threshold pace. The run supplies the running-specific stimulus.
• Friday: Rest.
• Saturday: 18 km long run, easy.
• Sunday: 45 min easy spinning, zone 2, no standing — active recovery instead of a stimulus.

That is 36 running kilometres plus two classes — and in total closer to 45 km of running equivalent than it looks. Anyone who adds the classes on top of an unchanged running plan jumps from 60 to 90 TSS per week, which is the range where injuries happen. How to judge such jumps is covered in the acute:chronic workload ratio.

Technique: five points that get lost in class

Class bikes adjust in broad steps, and most participants set them wrong. That is the most common reason for knee and back pain after classes — not the load itself. Five points to check before your first pedal stroke:

• Saddle height: With the leg extended at the bottom of the stroke, the knee should be almost straight without the pelvis rocking. Too low is the standard error and loads the kneecap.
• Saddle fore-aft: With the crank horizontal, the kneecap should sit vertically above the pedal axle. Too far forward presses into the knee; too far back, into the lower back.
• Handlebar height: At or above saddle height for beginners. A low bar looks sporty but forces a position most people cannot hold for 60 minutes.
• Cadence: 80 to 100 rpm as the base cadence. Grinding at 60 rpm with heavy resistance is strength work at the knee, not endurance training. "More resistance" from the instructor does not mean "pedal slower".
• Foot position: Cages or clipless pedals, ball of the foot on the pedal axle, knee in line with the foot. No inward collapse — that is the second most common knee killer after a saddle set too low.

One point that often gets missed: the flywheel. A heavy flywheel (18 to 22 kg) feels closer to riding outdoors, a light one responds more directly to surges. For runners using spinning as cross-training, a light flywheel at high cadence is the better choice — it resembles the running movement pattern more than a heavy, slow grind.

What spinning does not deliver

Three limits worth knowing before you put classes into your plan. They are not arguments against spinning — they are arguments against wrong expectations.

• No running-specific adaptation. Running is impact loading with passive energy return from tendons and fascia. Cycling is pure compressive movement without impact. Two months of spinning alone costs running economy and load tolerance in the support structures — even if the form curve looks good. Details in running economy.
• No substitute for volume. The decisive adaptation for marathon and gran fondo is the ability to stay economical for two to five hours. That needs duration, not intensity. A 60-minute class cannot trigger that adaptation, however hard it is.
• No reliable numbers. The calorie and distance displays on class bikes are modelled estimates without power measurement. Anyone steering energy balance with them works with a 10 to 20 percent error. For steering, the Training Stress Score is the more dependable figure — even though it too is calculated from estimated intensity and duration.

Common mistakes

• Adding classes instead of swapping them in. The classic error: the running plan stays unchanged and two classes go on top. That is a 30 to 40 percent load jump — exactly the range where overuse injuries appear.
• Racing every class. Anyone who always rides in the top third of heart rate turns a base format into a permanent intensity session. Four weeks later the form curve is flat and recovery is permanently incomplete.
• Setting the bike up wrong. Saddle too low, bars too low, foot too far forward — and three weeks later comes the knee pain. Setup matters more than the class.
• Introducing it during race preparation. New stimuli belong in the base phase. Starting spinning four weeks before a marathon brings unfamiliar muscular fatigue exactly when it costs most. How the final weeks should look is covered in tapering.
• Underestimating dehydration in class. In a heated room with music you sweat considerably more than outdoors at 12 degrees. 500 to 900 ml per hour is realistic — see hydration for running.
• Booking spinning as strength training. Heavy resistance at 60 rpm is no substitute for squats and deadlifts. Tendon stiffness and bone density need axial load — see strength training for runners.

How Peakora places indoor sessions

In the Peakora engine a spin session is not a special case but a bike session with an estimated intensity. You enter duration and perceived exertion, the engine derives a TSS value and books it into the load curve. That answers the question classes cannot answer themselves: how much does this hour cost inside my week?

Concretely: a 60-minute class lands at 50 to 80 TSS in the curve — roughly the same as a 12-kilometre easy run. Anyone who sees that stops adding two classes on top and starts swapping them in. The form curve (TSB) shows within two weeks whether the combination of running and indoor cycling works out or whether recovery stays permanently negative. And because the engine carries the session as a bike stimulus rather than a running stimulus, the weekly distribution stays honest: running kilometres are not replaced by class minutes, only supplemented. How bike and run stimuli are combined is covered in the glossary entries on TSS, CTL and TSB.

Frequently asked questions about spinning

Are spin classes good endurance training?

Yes, but only for base and threshold work. A 45 to 60 minute class equals roughly 50 to 80 TSS and sits at 75 to 85 percent of maximum heart rate for much of it. That is a useful additional stimulus, but no replacement for long easy sessions.

Can spinning replace a run?

No, not completely. Cycling is not running-specific: impact load, foot strike and the passive support structures are not trained. As cross-training during injury or as a second session on a double day, spinning works well.

How many calories does an hour of spinning burn?

Realistically 450 to 700 kilocalories for 60 minutes at an average of 150 to 200 watts. The displays on class bikes are modelled estimates and typically run 10 to 20 percent high.

Why do I get sore after spinning but not after running?

Because classes mix high cadence at high resistance, long standing phases and repeated surges — loads that running does not produce. The soreness reflects unfamiliar local strain, not better fitness.

How often per week should I spin?

Once or twice a week as a supplement. If you race bikes or do triathlon, two classes per week work as the winter intensity stimulus — on top of one long easy ride, not instead of it.