Every runner hits this crossroads eventually: Should you focus on speed or training volume? Is it better to push the pace or stay out longer? It’s a choice that can mean the difference between steady progress and a frustrating plateau.
Here’s how to decide when to run harder, when to go longer, and what each approach does to your body.
Contents
What happens when you run harder?
Running harder—meaning at higher intensities like tempo runs, intervals, or hill sprints—has a measurable impact on your cardiovascular system and muscle efficiency.
High-intensity runs improve your VO₂ max, or the maximum amount of oxygen your body can use during exercise. That means you can run faster at the same effort.
These workouts also raise your lactate threshold, helping you tolerate and clear fatigue-causing byproducts more effectively.
You’ll also burn more calories per minute. According to the Harvard Medical School calorie chart, a 155-pound (70 kg) person burns about 298 calories in 30 minutes of running at a 10-minute-per-mile pace (around 6:12 min/km). Increase the pace to 6 minutes per mile (about 3:44 min/km), and that same runner burns approximately 562 calories in the same amount of time.
But intensity comes at a cost. Running harder stresses the musculoskeletal system and nervous system more. Without enough recovery, this can lead to overtraining or injuries like shin splints and tendonitis. That’s why most experts limit hard sessions to one, maybe two, times a week—max.
What happens when you run longer?
Long, slow runs are the foundation of endurance training. They increase mitochondrial density (your cells’ energy producers), expand your capillary network (better oxygen delivery), and teach your body to burn fat more efficiently.
They also toughen up your mental game. Spending 60–90 minutes on your feet requires patience, mental stamina, resilience, and focus—skills that translate directly to race day.
Compared to speed work, longer runs come with a lower per-minute injury risk due to reduced impact forces. But they still stress the body—especially joints and tendons—so volume should be increased gradually.
Related: At What Pace Should You Run Easy and Long Runs
Match your training to your goal
Your ideal focus depends on what you’re training for:
- Chasing a faster 5K or 10K? You’ll need targeted speedwork: intervals, hill repeats, tempo runs, fartleks. Shorter races rely heavily on your ability to buffer lactate and maintain top-end pace.
- Training for a half or full marathon? Time on your feet matters more than raw speed. Long runs teach your body to stay efficient under fatigue, and midweek mileage builds resilience.
- Running for weight loss or general fitness? Studies suggest a mix of high and low-intensity runs is most effective. Longer runs burn more total calories, but hard efforts elevate post-run calorie burn through EPOC (excess post-exercise oxygen consumption), often called the afterburn effect.
Why most runners need both
Speed and endurance are training partners. Endurance training helps you go longer; speedwork helps you go faster with less effort. Most PRs happen when both are in place—not just one.
Incorporating both keeps training fresh and prevents plateaus. Runners who skip speedwork tend to stall at a comfortable pace. Runners who avoid long runs may struggle with late-race fatigue.
Even elite marathoners like Eliud Kipchoge combine weekly long runs with track intervals and tempo workouts. Recreational runners should too—but with less volume and more recovery.
How to balance hard vs. long
One proven framework: the 80/20 rule. That means about 80% of your weekly mileage should be at low intensity, while the remaining 20% can be moderate to hard. This principle is backed by research on both elite and amateur runners, showing improvements in performance and lower injury risk.
For example, if you run 25 miles (40 km) per week, only about 5 of those miles (8 km) should be “hard”—the rest should feel easy or moderate. Running hard too often leads to stagnation or breakdown.
Also, don’t combine intensity and volume. For example, a 15-mile (24 km) tempo run might sound impressive—but it’s a recipe for burnout. Keep hard runs shorter and focused, and let long runs stay mostly easy.
Space out hard efforts with at least 48 hours of recovery in between.
Common mistakes to avoid
Too many runners fall into one of two traps: going hard every day or running long without variation.
Other mistakes:
- Skipping recovery: Progress happens when you rest.
- Ignoring fatigue: If your legs feel heavy day after day, back off.
- Copying others: Just because your friend runs 40 miles (64 km) a week doesn’t mean you should. Training is individual.
Use Rate of Perceived Exertion (RPE) or a heart rate monitor to stay honest about intensity.
Related: 35 Common Running Mistakes and How to Avoid Them
Focus on the big picture
You don’t have to choose between running harder or longer, but you do need to train with purpose and align your training with the type of performance or result you want to see.
Use your weekly long run to build endurance, and include one hard session (like intervals or a tempo run) to develop speed and efficiency. Keep the rest of your runs easy enough that you can hold a conversation.
Follow the 80/20 rule: most of your weekly mileage should feel manageable. Space out your harder days with recovery runs or cross-training.
Get the balance between speed and endurance right, and the results will follow.
