The Great Cardio Debate

Few topics in fitness generate more debate than cardio. Does it kill gains? Is HIIT superior to steady-state? Should you do it fasted? The evidence paints a clearer picture than social media would have you believe.

Understanding Cardiovascular Training

Cardiovascular training is any sustained activity that elevates your heart rate, improving the efficiency of your heart, lungs, and circulatory system. The benefits extend far beyond fat loss:

• Reduced all-cause mortality — A 2019 meta-analysis in the British Journal of Sports Medicine found that any amount of running was associated with a 27% lower risk of death from all causes
• Improved heart health — Lower resting heart rate, reduced blood pressure, improved cholesterol profile
• Better recovery between sets — A stronger cardiovascular system clears metabolic byproducts faster
• Enhanced mental health — Regular cardio reduces symptoms of anxiety and depression (Schuch et al., 2018)
• Improved insulin sensitivity — Better glucose uptake and nutrient partitioning

The Heart Rate Zones

Understanding training zones helps you target the right adaptations:

Zone	% Max HR	Feel	Primary Fuel	Purpose
Zone 1	50–60%	Very easy, conversational	Fat	Recovery, warm-up
Zone 2	60–70%	Comfortable, can hold a conversation	Mostly fat	Aerobic base building
Zone 3	70–80%	Moderate, can speak in short sentences	Fat + carbs	Tempo/threshold training
Zone 4	80–90%	Hard, can only say a few words	Mostly carbs	VO2max improvement
Zone 5	90–100%	Maximum effort, can’t speak	Carbs (anaerobic)	Peak power, sprints

Estimating max heart rate: The simplest formula is 220 − your age, though individual variation can be ±10–15 bpm. More accurate testing requires a graded exercise test.

LISS: Low-Intensity Steady State

What it is: Sustained exercise at Zone 2 (60–70% max HR) for 30–60+ minutes. Examples: brisk walking, easy cycling, swimming at a moderate pace, light jogging.

Benefits:

• Burns a high percentage of fat relative to carbohydrates
• Minimal impact on recovery from weight training
• Low injury risk and accessible to all fitness levels
• Builds aerobic base — the foundation for all other training
• Can be done daily without significant fatigue

Drawbacks:

• Time-intensive for significant calorie burn (~300–500 kcal/hour)
• Can become monotonous
• Less EPOC (excess post-exercise oxygen consumption) compared to HIIT

Who should prioritize LISS:

• Anyone building an aerobic foundation
• Lifters wanting cardio that doesn’t interfere with recovery
• People with joint issues or those new to exercise
• Anyone doing 4+ strength sessions per week

HIIT: High-Intensity Interval Training

What it is: Short bursts of near-maximal effort (Zone 4–5) alternated with recovery periods. Example: 30 seconds all-out sprint, 60 seconds walk, repeated 8–10 times.

Benefits:

• Time-efficient — significant cardiovascular benefits in 15–25 minutes
• Higher EPOC — elevated metabolism for hours after the session
• Improves VO2max more rapidly than steady-state cardio
• Preserves muscle mass better than long-duration steady-state (when volume is controlled)

Drawbacks:

• Highly fatiguing — competes with recovery from strength training
• Higher injury risk, especially for beginners
• Requires sufficient fitness base to perform safely
• Can’t be done daily — 2–3 sessions/week maximum

A proper HIIT session:

• Warm-up: 5 minutes easy pace
• Work interval: 20–40 seconds at 85–95% max effort
• Rest interval: 40–120 seconds at easy pace
• Rounds: 6–10 total
• Cool-down: 5 minutes easy pace
• Total time: 20–30 minutes

LISS vs HIIT: What the Science Says

A 2017 meta-analysis by Keating et al. found that when total calorie expenditure is matched, LISS and HIIT produce virtually identical fat loss. The real-world difference comes down to time: HIIT achieves similar benefits in less time, but at the cost of more fatigue.

For lifters specifically, the interference effect matters. A landmark review by Wilson et al. (2012) in the Journal of Strength and Conditioning Research found that:

• Running-based cardio causes more interference with leg hypertrophy than cycling
• Higher cardio volumes (>3 sessions/week) reduce strength and hypertrophy gains
• Separating cardio and strength sessions by at least 6 hours minimizes interference
• Cycling is generally preferable to running for lifters (less eccentric muscle damage)

The Optimal Cardio Plan for Lifters

Based on current evidence, here’s a practical framework:

Primary goal — Muscle building:

• 2–3 sessions of Zone 2 LISS per week (20–30 min each)
• Walking is ideal — 8,000–10,000 steps daily
• Limit HIIT to 1 session/week if desired
• Separate from leg training by 24+ hours

Primary goal — Fat loss:

• 3–4 sessions of LISS per week (30–45 min each)
• 1–2 HIIT sessions per week
• Prioritize daily step count (10,000–12,000 steps)
• Keep total cardio moderate to preserve muscle

Primary goal — General health:

• 150 minutes of moderate-intensity cardio per week (WHO guidelines)
• Or 75 minutes of vigorous-intensity cardio per week
• Mix of LISS and HIIT based on preference
• Include 2+ strength sessions per week

Fasted Cardio: Myth vs Reality

Fasted cardio (exercising before eating) has been promoted as a fat-burning hack for decades. However, a 2014 study by Schoenfeld et al. in the Journal of the International Society of Sports Nutrition found no difference in fat loss between fasted and fed cardio when total daily calories were controlled.

Your body compensates over 24 hours — burning more fat during a fasted session means burning more carbs later, and vice versa. Total daily energy balance is what determines fat loss, not the fuel source during a single session.

Common Cardio Mistakes

1. Doing too much — Excessive cardio increases cortisol, suppresses testosterone, and eats into recovery capacity
2. Only counting gym cardio — Daily NEAT (walking, stairs, general movement) often burns more calories than formal sessions
3. Using cardio to “undo” bad nutrition — You cannot outrun a bad diet. A 20-minute run burns roughly one cookie’s worth of calories
4. Skipping it entirely — Cardiovascular health is essential. Even dedicated lifters need some cardio for longevity and heart health
5. Going too hard too often — Most cardio should be easy (Zone 2). Save high-intensity work for 1–2 sessions per week

References

• Keating, S.E., et al. (2017). A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity. Obesity Reviews, 18(8), 943–964.
• Wilson, J.M., et al. (2012). Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293–2307.
• Schoenfeld, B.J., et al. (2014). Body composition changes associated with fasted versus non-fasted aerobic exercise. Journal of the International Society of Sports Nutrition, 11(1), 54.
• Schuch, F.B., et al. (2018). Physical activity and incident depression: a meta-analysis of prospective cohort studies. American Journal of Psychiatry, 175(7), 631–648.