In fitness, some questions never seem to die. Forget the ‘strength vs. cardio’ debate. The real question is ‘when’ not ‘if’.

Concurrent training—the practice of combining strength and cardiovascular work—remains one of the most misunderstood aspects of program design in the fitness industry. While most fitness professionals recognize the importance of both modalities, the science behind their interaction reveals a far more complex relationship than simply alternating between the squat rack and the treadmill.

The truth is, effective concurrent training requires a nuanced understanding of cellular pathways, energy system specificity, and training timing. Just as we wouldn't expect optimal results from random exercise selection in a strength program, we shouldn't expect optimal results from randomly combining strength and cardio work without considering their biological interactions.

In this article, we'll examine the science behind concurrent training, explore the crucial distinction between optimal and practical application, and provide clear, actionable guidelines for program design. Whether you're working with competitive athletes requiring precise periodization or general population clients seeking overall fitness, understanding these principles will dramatically impact your ability to deliver results.

Let's dive into the research and practical applications that will help you master the art and science of concurrent training.

What is Concurrent Training?

Concurrent training is the practice of combining both resistance (strength) training and endurance (cardiovascular) training within the same periodized program. While this definition seems straightforward, there's often a disconnect between what research tells us about concurrent training and how it's understood in the mainstream fitness industry. Many fitness professionals assume that simply doing strength work and cardio in the same week, or even the same session, constitutes effective concurrent training. However, the science reveals a more nuanced picture that can dramatically impact your clients' results.

The Truth About Training Frequency and Timing

Here's what the research actually shows: strength and cardio can be trained in the same week, and even on the same day, but they're not as effective when trained in the same session. This distinction is crucial for program design. While it's perfectly viable to schedule strength training in the morning and cardio in the evening, or alternate days throughout the week, combining them in a single session creates interference effects that can compromise both strength and endurance adaptations.

The Cellular Competition: AMPK vs. mTOR

The reason concurrent training within the same session is less effective lies in cellular signaling pathways. Strength and cardio training trigger different, and often conflicting, adaptations at the cellular level:

mTOR Pathway (Strength Training)

• Promotes protein synthesis

• Drives muscle growth and strength gains

• Enhanced by resistance training and adequate nutrition

AMPK Pathway (Endurance Training)

• Promotes cellular energy efficiency

• Drives mitochondrial adaptations

• Can inhibit mTOR when highly activated

When both pathways are activated simultaneously through concurrent training in the same session, they compete for cellular resources, leading to what researchers call "interference effects." This cellular competition explains why athletes who try to maximize both strength and endurance simultaneously often see blunted results in both areas.

Cardio vs. Conditioning: Understanding Energy System Specificity

Not all "cardio" is created equal. Understanding the difference between traditional cardiovascular training and metabolic conditioning is essential for effective program design. Traditional Cardio typically refers to steady-state aerobic exercise that primarily targets the oxidative energy system. Think long runs, bike rides, or extended elliptical sessions. Conditioning is more varied and can target different energy systems depending on the work-to-rest ratios and intensity. This is where energy system specificity becomes critical for your training goals.

Energy Systems and Training

Each energy system pairs differently with strength training objectives:

ATP-CP System (0-10 seconds)

• Provides immediate energy for maximum power output

• Pairs excellently with strength and power training

• No oxygen required, no interference with strength adaptations

• Think heavy singles, explosive movements, and short sprints

Glycolytic System (10 seconds - 2 minutes)

• Provides energy for high-intensity, short-to-medium duration efforts

• Pairs well with volume-based strength training

• Can complement hypertrophy-focused programs

• Examples include circuit training and moderate-duration intervals

Aerobic System (2+ minutes)

• Provides sustained energy for longer, lower-intensity activities

• Generally does NOT pair well with strength training due to interference effects However, can complement bodyweight flow work and mobility training

• Best kept separate from strength-focused sessions

Making Concurrent Training Work: Goal-Specific Programming

Concurrent training can be highly effective when properly planned and aligned with specific training goals. The key is understanding which combinations work synergistically rather than creating interference.

For Muscle Gain/Hypertrophy:

• Prioritize low-to-moderate intensity steady-state work

• Time aerobic work 6+ hours from strength sessions

• Focus on short anaerobic sessions post-strength training

For Maximum Strength:

• Emphasize low-impact aerobic work for recovery

• Use alactic conditioning (ATP-CP system) for power development

• Avoid high-intensity cardio on or near strength training days

For Fat Loss:

• Combine HIIT and steady-state work strategically

• Post-workout conditioning can enhance caloric expenditure

• Maintain strength training frequency to preserve lean mass

For Sport-Specific Performance:

• Replicate sport energy demands through specific conditioning

• Periodize training to peak both systems appropriately

• Consider skill/speed work as part of the conditioning component

For Endurance Building:

• Use progressive aerobic base training with intervals

• Maintain some strength work to prevent injury

• Focus on muscular endurance rather than maximum strength

Download the complete Cardio & Conditioning Integration chart below for easy reference in your program design.

Practical vs. Optimal: Real-World Application for General Population

Clients While the science of interference effects is important to understand, it's equally important to recognize the difference between optimal training for competitive athletes and practical training for your typical personal training clients. Most personal training clients exercise 2-3 times per week and are training for overall health and fitness, and NOT competitive performance. These clients aren't training daily where interference effects would significantly impact their progress. For this population, there's nothing inherently wrong with getting "a little bit of everything" in their training sessions.

A Realistic Approach for General Population Clients:

Rather than rigidly separating training modalities, consider an alternating emphasis approach:

• Day 1: Aerobic Emphasis - Primary focus on cardiovascular training with some strength/resistance components

• Day 2: Anaerobic Emphasis - Primary focus on strength/power training with aerobic components (like a cardio cooldown)

• Day 3: Balanced or repeat the cycle

This approach allows clients to develop both strength and cardiovascular fitness within their limited training frequency while still respecting the principles of energy system specificity. The key is having a clear primary emphasis each session rather than trying to maximize both simultaneously. Remember: for general population clients, consistency and adherence often trump perfect optimization. A program they'll actually follow is infinitely better than a theoretically perfect program they'll abandon.

Key Takeaways for Fitness Professionals

1. Context matters - Distinguish between competitive athletes (optimal) and general population clients (practical)

2. Timing matters more than frequency - Same day can work (with AM/PM sessions), same session often doesn't

3. Energy system specificity drives adaptation - Match your conditioning to your primary goal

4. Cellular signaling pathways compete - Understand the AMPK/mTOR interference

5. Goal alignment is essential - Use the framework provided to guide program design

6. Practical adherence beats perfect optimization - Design programs clients will actually follow

Putting It Into Practice

Use the attached Cardio & Conditioning Integration chart as your guide for implementing these concepts with your clients. This reference tool provides specific recommendations for frequency, timing, and exercise selection based on primary training goals. Remember: effective concurrent training isn't about doing more, it's about doing the right things at the right times to maximize adaptations while minimizing interference.

Trainer Edge Newsletter is published by Ideal Strength. For more educational resources for fitness professionals, sign up for the newsletter: Trainer Edge Newsletter