What is the difference between intervals and tempo runs?

Tempo runs and intervals train different energy systems and produce different adaptations. Tempo runs are sustained continuous efforts — typically 20-40 minutes at 'comfortably hard' pace (85-88% of max HR), which is near your lactate threshold. The goal is teaching your body to clear lactate at faster speeds, raising the pace you can hold without blowing up. Intervals are short, hard repetitions at 5K pace or faster (90-95% of max HR), typically 400m to 1600m in length, with active rest between. The goal is to improve VO2max (oxygen uptake) and running economy. Example tempo session: 20 minutes at half-marathon pace, continuous. Example interval session: 5 x 1000m at 5K pace with 90 seconds jog recovery. You feel different during each: tempo is hard-but-controlled breathing; intervals leave you gasping for the first 30 seconds of each recovery. Most training plans for 10K-marathon distances include one tempo and one interval session per week during the build phase. Do both, not just one. Tempo alone makes you durable but capped; intervals alone make you fast but fragile. The combination is what lifts race times meaningfully.