Ask a Personal Trainer: “Selecting The Right Weight”


The Evidence


Research by Hacket et al. (2016) tested a group of 53 men and 28 women, with different levels of resistance training experience, to see how accurately they were able to predict the number of reps they could perform with a given weight on both a leg press and chest press resistance machine.


The participants were asked to perform multiple sets of 10 reps, with 70% and 80% of their maximum, on each resistance machine respectively. After completing each set the participants were asked how many more reps they believed they could perform. Participants continued performing sets until they couldn’t complete a full set of 10 repetitions.


Results revealed that all participants were more accurate as they came closer to maximum (with only 3 more reps being possible). However, in sets where more than 5 reps were still possible, participants were significantly inaccurate in approximating how many reps they could still perform. Participants significantly underestimated their ability by 3-5 reps per set on average. For example, a participant would report that they believed another 4 reps. When tested, they went on to perform another 10 reps! Accuracy for the leg press machine was found to be worse than for the chest press machine.


The Meaning


Stress (even eustress) and physical discomfort, as experienced through resistance training, blur our ability to accurately judge our capability. Performing sets of 10 reps on a leg press machine induces far greater discomfort than 10 reps on a chest press machine. This is demonstrated in the results as participants’ accuracy worsened when performing the exercise that induced greater discomfort. More discomfort + more effort = less accuracy!



The Application


Our personal training clients, and those I coach online, often find self-selecting the correct weight for each exercise challenging. I’ve been training myself for around ten years and still find myself attempting exercises with weights I can’t lift for the reps I planned… Although, perhaps this is simply my ego!


There are several key points we can take and apply from this study:

1.     Understanding that effort/stress seems to blur our ability to achieve our potential, it makes sense to assume we’re typically capable of more than we believe/feel. This might be especially true if looking objectively at how we feel/think as we enter the gym. If you’ve had a tough day, step back and acknowledge how this might affect your ambition going in to your workout.

2.     Even if you don’t use a program written for you by a professional, it’s worth considering booking a session periodically to “re-evaluate” your understanding of what you are truly capable of in terms of effort and accuracy. After all, the correct weight means better results.

3.     With those I coach online, I occasionally add an AMRAP (As Many Reps As Possible) Set to a key exercise in the program. Typically, this will be a compound movements near the beginning or middle of the workout program. This will allow immediate insight as to the number of reps you were truly capable of. You can then be brave and adjust the weights you use accordingly for the next workout in your program.


Thank you so much for reading.

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