Published 31 May 2020 Luke Kane Founder & CEO, Exercise Physiologist

Reviewed by Antonia Kendrick Allied Health Team Leader & Head Physiotherapist

Predicting Intensity of Resistance Training

Question: “How does that weight feel?”

This is a frequent question you will hear our practitioners asking. If the weight is too easy for certain exercises it means the intensity of effort will be too low, and consequently the adaptation you are trying to achieve will suffer. Intensity is one the most important variables to improve body composition, strength and overall health and fitness. Research investigating the individual responses to resistance training in terms of effort has shown that exercise practitioners and strength and conditioning coaches can predict how hard clients and athletes are working and can in fact avoid the risk of overtraining and musculoskeletal injuries.

What is intensity of effort and how is it measured?

Intensity of effort literally refers to how hard you are working during exercise. It is often measured subjectively using a scale called rate of perceived exertion (RPE), which is a 6-20 scale or 10 scale assessing fatigue during exercise. The 0-10 scale is often used for assessing resistance training intensity. Unfortunately, this scale is not very sensitive to assessing fatigue during strength training sessions, as noted in a paper by Hackett et al., 2012: “…RPE scores at volitional fatigue were less than maximal for bench press and squat exercises”.

Research / Evidence

The paper by Hackett et al., 2012 looked at using a new scale to assess the intensity of effort / muscular fatigue in strength trained men.

Purpose: “To determine the validity of a novel subjective estimated-repetitions-to-failure for predicting muscular failure during resistance exercise. To do this we compared estimated-repetitions-to-failure (ERF) with actual-repetitions-to-failure and related both to RPE across multiple resistance-exercise bouts in experienced resistance-trainers”

The authors gathered 17 strength-trained (bodybuilders) men (age 32.3 ± 4.7 years) and they underwent a training protocol which involved 2 sessions of 5 sets x 10 reps at 70%1RM* with 5 minutes rest between sets for the bench press and squat exercises. After each set was performed participants were shown the both the RPE and ERF scales and asked to score each. After the participants rated each scale they performed repetitions to failure and this was referred to actual-repetitions-to-failure (ARF).

Results

There were “high positive correlations between ERF and ARF for all subjects” and during the later sets (3, 4 and 5), the ERF “accurately predicted the number of ARF” for both exercises.

Essentially, as the training session progressed, the accuracy of participants estimating their reps to failure increased.

What does this mean for you?

With this information, trainers can accurately predict a level of fatigue in clients for certain exercises based on their estimated reps to failure in the later sets of an exercise. This will allow the modification of training loads to ensure that fatigue is not reached prematurely and that optimal adaptation can occur without overtraining. Therefore, if a weight is too light or heavy, let the trainers know because the intensity of effort will be affected and you might fatigue too quickly and start to overtrain, which can affect the rest of the session or be working at too low an intensity. Most of the time the trainers will know what weights you are capable of and if technique starts to deteriorate in the early sets it is usually a sign that the weight is too heavy and can be reduced.

How to Use ‘Estimated Reps to Failure’

Estimated reps to failure is an incredibly useful guide to indicate the right intensity to be used for resistance to stimulate hypertrophic adaptations. The main advantage of using this scale is increasing the awareness of the lifter on the importance of lifting at a submaximal intensity. If you haven’t had a look at our extensive series on strength, we suggest that you do in order to get a comprehensive understanding as to why this sub max intensity so important. It often flies in the face about what most people think about when they go to the gym (i.e. heavier & harder is better always), but that’s what intelligent training is all about.

A general guide

• When you finish an exercise give yourself an estimate as to how many more repetitions you thought you could’ve performed at that weight if you had to go ALL OUT (this may require some experimentation to see how close your estimates are to actual ability).
• When you estimate that you can do more than 5 reps with a weight, it’s a sign that you might want to increase the weight being lifted in order to maximise the hypertrophic benefits.
• If you feel you could get less than 2 reps with that weight, then you may want to look at using a lighter weight.
• When observing the exercise being performed, pay attention to the speed at which it is being performed. This will give another clue as to how much you might be able to lift.
• This tool is mainly useful for hypertrophic adaptations and is a simple guide to ensure intensities are right without needing to record weights week to week. 

Reference: Hackett, D. A., Johnson, N. A., Halaki, M., & Chow, C. (2012). A novel scale to assess resistance-exercise effort. Journal of Sports Sciences, 30(13), 1405. doi:10.1080/02640414.2012.710757

*1RM = 1 repetition maximum

About the authors

Written by

Luke Kane

Founder & CEO, Exercise Physiologist

Exercise physiologist and Founder & CEO of MTP Health, which he established in 2012, with a career built around movement, rehabilitation and healthcare.

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Reviewed by

Antonia Kendrick

Allied Health Team Leader & Head Physiotherapist

Head Physiotherapist and Allied Health Team Leader at MTP Health, with a genuine, patient-focused approach to physiotherapy, rehabilitation and patient education.

View profile