Power meters are the gold standard for training precision. They're also expensive. If you don't have one, that's not a reason to skip structured training. Heart rate and RPE both work, and several apps are designed around them.
Heart rate is a legitimate training tool
Heart rate monitors cost $30-80 and provide genuinely useful data. Yes, heart rate is affected by temperature, caffeine, fatigue, and stress (more on HR vs power). But it's accurate enough for structured training, especially for Zone 2 endurance rides where pacing by feel is unreliable.
For most recreational cyclists, a heart rate monitor and a good app gets you 80% of the benefit of a power meter setup. The other 20% is precision that matters more at competitive levels.
RPE works too
Rate of Perceived Exertion is a 1-10 scale. It's free, always available, and research shows experienced athletes estimate zones by feel with reasonable accuracy. Less precise than HR, but better than guessing.
Apps that work without power
Nivvy
Built to work with whatever you have. Power, heart rate, or RPE. The app adjusts training plans and Training Score calculations based on your data source.
With heart rate: HR zones for workout targets, estimated training stress from HR data. With RPE: perceived effort zones, slightly lower score ceiling (less data certainty), but all features work.
Leagues, streaks, AI coaching, and the Training Score all function regardless of equipment. You miss some precision but none of the features.
Free (Pro $10/month, Coach Pro $25/month)
Zwift
Works with a smart trainer (virtual power) or basic trainer with speed sensor (estimated power). No standalone power meter needed. Also has heart rate-based workouts.
$15/month
Strava
Records GPS and heart rate. Provides estimated power using grade, speed, and rider weight. The estimates are rough but useful for trends. Relative Effort uses HR data to estimate training load without power.
Free (Summit $12/month)
TrainerRoad
Works best with power but supports heart rate-based training and estimated power from basic trainers.
$20/month
Should you eventually get a power meter?
If you're racing or want to optimize every detail, yes. For fitness, fun, and general improvement? Heart rate is plenty. Don't let equipment be the reason you don't start structured training.
The hierarchy: any data is better than no data. Use what you have. Upgrade when it makes sense.