Exercise Intensity Guide: How Hard Should You Train?

Intensity is one of the most important—and most misunderstood—training variables. Training too easy won't produce results; training too hard leads to burnout and injury. This guide explains how to calibrate intensity for different goals and track it effectively.

Understanding Intensity

What is training intensity?

In strength training:

• How heavy the weight is relative to your max
• Measured as % of 1RM (one-rep max)
• Also measured by RPE (rate of perceived exertion) or RIR (reps in reserve)

In cardio:

• How hard you're working
• Measured by heart rate, pace, or perceived effort
• % of max heart rate or VO2 max

Common confusion:

• "Intense" doesn't mean "exhausting"
• High intensity = heavy or fast
• High effort = working hard (can be any intensity)

Intensity Measurement Methods

Percentage of 1RM (Strength)

What it is: Weight as percentage of your max lift

Example: If your squat max is 200 lbs:

• 80% = 160 lbs
• 70% = 140 lbs
• 60% = 120 lbs

Guidelines: | % of 1RM | Typical Reps | Training Effect | |----------|--------------|-----------------| | 90-100% | 1-3 | Max strength | | 80-90% | 3-6 | Strength | | 70-80% | 6-10 | Strength-hypertrophy | | 60-70% | 10-15 | Hypertrophy | | 50-60% | 15-20+ | Endurance |

RPE (Rate of Perceived Exertion)

What it is: How hard the set felt, 1-10 scale

Scale:

• RPE 10: Maximal effort, no more reps possible
• RPE 9: Could do 1 more rep
• RPE 8: Could do 2 more reps
• RPE 7: Could do 3 more reps
• RPE 6: Could do 4+ more reps

Advantages:

• Accounts for daily variations
• No need to know 1RM
• Adjusts automatically

RIR (Reps in Reserve)

What it is: How many reps you could have done

Example:

• "3 RIR" = stopped 3 reps before failure
• "1 RIR" = could have done 1 more
• "0 RIR" = went to failure

Same concept as RPE, different framing:

• RPE 10 = 0 RIR
• RPE 9 = 1 RIR
• RPE 8 = 2 RIR

Heart Rate (Cardio)

Zones based on max heart rate (220 - age = rough estimate):

| Zone | % Max HR | Feel | Use For | |------|----------|------|---------| | 1 | 50-60% | Very easy | Recovery | | 2 | 60-70% | Easy, conversational | Base building | | 3 | 70-80% | Moderate, harder to talk | Tempo work | | 4 | 80-90% | Hard, minimal talking | Threshold | | 5 | 90-100% | Very hard, unsustainable | Intervals |

Talk Test (Cardio)

Simple assessment:

• Can hold conversation = easy/moderate
• Sentences only = moderate/hard
• Few words only = hard
• Can't talk = very hard

Intensity for Different Goals

For Strength

What research shows:

• Need to train heavy (>75% 1RM) for max strength
• Sets of 1-6 reps most effective
• RPE 7-9 typical (not always to failure)
• Quality > quantity

Example workout:

• Squat: 5x3 at RPE 8
• Bench: 4x4 at RPE 8
• Row: 4x5 at RPE 7

For Hypertrophy (Muscle Size)

What research shows:

• Wide range of intensities work (40-80% 1RM)
• Key is taking sets close to failure (1-3 RIR)
• 6-20 reps most common
• Volume matters more than exact intensity

Example workout:

• Leg press: 4x10 at RPE 8
• RDL: 3x12 at RPE 8
• Leg curl: 3x15 at RPE 9

For Endurance

What research shows:

• Most training should be easy (Zone 2)
• Some high-intensity work (Zone 4-5) is beneficial
• 80/20 rule: 80% easy, 20% hard

Example week:

• 3 easy runs (Zone 2)
• 1 tempo run (Zone 3-4)
• 1 interval session (Zone 4-5)

For Power

What research shows:

• Moderate loads (50-70% 1RM) moved fast
• Full recovery between sets
• Quality and speed, not fatigue
• Stop before form degrades

Example:

• Box jumps: 5x5 with full recovery
• Power cleans: 6x3 at 60-70%
• Medicine ball throws: 4x6

How Hard Should You Train?

The effective intensity zone:

Too easy (RPE <6):

• Insufficient stimulus
• Won't produce adaptation
• Wasted time

Productive range (RPE 6-9):

• Challenging but sustainable
• Drives adaptation
• Where most training should be

Maximum/failure (RPE 10):

• Use sparingly
• Very fatiguing
• Increases injury risk
• Has diminishing returns

Recommended intensity distribution:

Most sets: RPE 7-8 (2-3 RIR) Some sets: RPE 9 (1 RIR) Occasional sets: RPE 10 (failure)

Why not always train to failure?

• Excessive fatigue
• Impairs recovery
• Reduces total volume capacity
• Increases injury risk
• Diminishing returns per set

Autoregulation

What it is:

Adjusting intensity based on how you feel that day.

How it works:

• Plan target RPE, not exact weight
• If feeling good, lift more
• If feeling bad, lift less
• Meet the RPE, adjust load as needed

Example:

Plan: Squat 4x6 at RPE 8

Good day:

• Warm up feels great
• Work sets at 165 lbs = RPE 8

Bad day:

• Warm up feels heavy
• Work sets at 155 lbs = RPE 8

Same productive stimulus, different loads.

Signs of Intensity Errors

Training too light:

• Not challenging
• No progression
• Easy recovery
• No soreness ever
• Not achieving goals

Training too hard:

• Always exhausted
• Frequent injuries
• Performance declining
• Dreading workouts
• Sleep problems
• Always sore

Just right:

• Challenging but doable
• Progressive improvement
• Recovering between sessions
• Enjoying training
• Some soreness, not excessive

Periodizing Intensity

Why vary intensity:

• Prevents staleness
• Manages fatigue
• Allows different adaptations
• Reduces injury risk

Simple periodization example:

Week 1: RPE 7 (building) Week 2: RPE 7-8 Week 3: RPE 8 Week 4: RPE 8-9 (peak) Week 5: RPE 6-7 (deload) Repeat

Within a workout:

• Main lifts: Higher intensity (RPE 7-9)
• Accessory work: Moderate intensity (RPE 7-8)
• Final exercises: Can push harder (RPE 9)

Practical Application

Calibrating your RPE:

Week 1: Estimate your RPE Week 2: Record whether you hit target reps Week 3: Adjust based on results

If you planned RPE 8 and got all reps easily → Was actually RPE 7 If you planned RPE 8 and barely got reps → Was actually RPE 9

Building RPE awareness:

Practice:

1. After each set, rate RPE before looking at results
2. Compare to what happened (did you hit reps?)
3. Refine your internal calibration

Over time: Your RPE estimates become very accurate

Key Takeaways

1. Intensity ≠ effort: They're related but different
2. Most training: RPE 7-8: Challenging but sustainable
3. Failure is a tool, not the goal: Use sparingly
4. Autoregulate: Adjust to how you feel that day
5. Track and calibrate: Learn your body's signals
6. Vary intensity: Periodize over weeks and months
7. Match intensity to goals: Strength needs heavy, endurance needs easy base
8. Recovery matters: Intensity you can't recover from is counterproductive

The best training intensity is the one that challenges you enough to adapt while allowing you to recover and come back stronger. Learn to read your body, track your performance, and adjust accordingly.