We may question the efficacy of dedicating extra hours to intense workouts. Does this lead to overtraining and impede progress, or will the additional time dedicated to lifting promote further muscle development?

Exercise scientist Dr. Mike Israetel, Ph.D., addressed these queries on July 30, 2024. He introduces the concept of the stimulus-to-fatigue ratio (SFR), which is pivotal in hypertrophy training and cardio.

In hypertrophy training, SFR measures the balance between muscle growth and the level of fatigue incurred. For cardio, it assesses the efficiency of fat burning relative to fatigue. Dr. Israetel recommends leveraging this ratio to optimize overall effort.

[Related: The 9 Best Exercises for Weight Loss]

Working Out Too Hard: Fact or Fiction?

Dr. Israetel provides an example of muscle-growth training, highlighting the journey from beginner gains to advanced challenges. Initially, beginners experience significant increases in strength and muscle size due to heightened stimulus levels.

However, as individuals approach their systemic adaptation limits, the rate of gains diminishes, and fatigue accumulates from the increased effort required. Dr. Israetel identifies three distinct approaches people take towards their training regimens in this context:

Tier 1: Training lightly yields minimal gains and negligible fatigue. Dr. Israetel recommends avoiding training at such a low intensity.

Tier 2: Training at 80 to 90% of capacity can lead to significant improvements, albeit accompanied by increased fatigue. The progression allows ample recovery time.

Tier 3: Training at full capacity yields minimal gains, accompanied by significant fatigue that might hinder progress the following week.

Per Dr. Israetel, training at 80 to 90% capacity yields the best results for optimal long-term growth.

Any less…you’ll get great results, but [not] the best results. Any more, it’s too much fatigue for too little extra stimulus.

Israetel recognizes that reaching failure during exercise is plausible, yet he points out that the stimulus-to-fatigue ratio is not optimal. “Mostly, you should train between three repetitions in reserves, two reps, and one rep in reserve,” says Israetel. “That’s the golden range that gives you your average best stimulus-to-fatigue ratio.”

Image via Shutterstock/PeopleImages.com – Yuri A

There are factors to consider when training to failure. “You can grind to 100% on occasion to test yourself. You can only really see how strong you are for reps if you push to failure…but most training sessions should be submaximal.”

Dietary Considerations

According to Dr. Israetel, aiming for 80 to 90% of the maximum sustainable calorie deficit is more effective for long-term leanness than striving for 100%. “Instead of going 100% maximum deficit, go to 80 or 90%,” said Israetel. “You’ll burn a ton of fat relatively sustainably because the fatigue will still be relatively low; thus, your stimulus-to-fatigue ratio is the highest.”

Wrapping Up

Dr. Israetel suggests challenging oneself through activities with a high stimulus-to-fatigue ratio.

Get as much out of it…relative to how much fatigue you accumulate relative to the cost.

Performing consistently long-term at 90% with a small fatigue cost “beats those who go 100% but burns out in a few weeks.”

Featured Image: PeopleImages.com – Yuri A / Shutterstock

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