Key Points:
- 70 young women were assigned to a 10-week training program with either constant or varied exercises.
- The constant exercise group trained the leg press and stiff-legged deadlift every session, while the varied exercise group rotated between three different quad and hamstring exercises.
- After ten weeks, there were no differences in quad or hamstring growth, or strength gains in the leg press (trained) and leg extension (non-trained).
***
When I first got into strength training two decades ago, exercise variation was kind of a big deal.
The exact reasons were a bit unclear, but it mostly had something to do with “keeping the muscles guessing”.
In recent years, the exercise variation hype seems to have cooled off a bit. Still, I don’t feel like we can close the book on it yet. And neither did a research team in Brazil, that recently published an excellent study of the matter, which I’ll be going over today.1
Which Is Better for Strength and Muscle Growth: Varied or Constant Exercises?
The researchers wanted to investigate if varied exercises were superior to constant exercises in terms of strength and muscle gains.
Here’s what they did.
Participants
90 young (mostly early 20s) women were enrolled in the study, and 70 completed it. The women were of normal weight and height and had not done resistance training for at least six months prior to the study.
The Training
The participants were randomized into one of two groups: constant exercises (CON) or varied exercises (VAR).
Both groups would train their lower body three times per week for ten weeks, with one quadriceps and one hamstring-dominant exercise.
But while the CON group would use the same two exercises (one for the quads and one for the hamstrings) in every workout, the VAR group rotated between three different exercises for each muscle group.
Here are their training programs.
| Monday | Wednesday | Friday | |
|---|---|---|---|
| CON | 1. Leg Press 2. Stiff-Legged Deadlift | 1. Leg Press 2. Stiff-Legged Deadlift | 1. Leg Press 2. Stiff-Legged Deadlift |
| VAR | 1. Leg Press 2. Stiff-Legged Deadlift | 1. Hack Squat 2. Lying Leg Curl | 1. Smith Machine Squat 2. Seated Leg Curl |
In every workout, they did 2 sets x 10–15 reps, and increased the weight when they could do more than 15 reps. They rested for two minutes between sets, and three minutes between exercises.
All training sessions were supervised by an instructor.
Also, before starting the ten-week training program, they did two weeks of familiarization training to learn the exercise technique and establish training weights. After the two weeks of familiarization, they underwent testing and then began their training programs.
Testing
The researchers conducted two different tests of max strength and took several measurements of muscle thickness using ultrasound.
The strength tests were a one-rep max in the leg press (which they trained) and in the leg extension (which they didn’t train).
They measured muscle thickness at three sites on the front and lateral sides of the quadriceps (at 30, 50, and 70% of the femur length), and at two sites on the hamstrings (50 and 70% of femur length).
The tests were performed before and after the ten weeks of training.
The Results
After ten weeks, here are the improvements.
Let’s begin with the front of the quadriceps muscle, which would be mainly the vastus intermedius.
Muscle thickness increased to a similar extent at all three sites in both CON and VAR.
Then on to the lateral (outer side) of the quadriceps, which would be the vastus lateralis – the biggest head of the quadriceps.
Same story here, with similar muscle growth across all measures:
And then finally the back of the thigh, the hamstrings. Once again, muscle growth was similar at both measurement sites.
Last but not least, the strength gains:
Here, too, gains were similar between groups in both the trained (leg press) and non-trained (leg extension) exercises.
My Thoughts on the Results
It’s always difficult to tell after you’ve learned the results, but I think these results were a mix of what I expected and what I didn’t expect.
Let’s review the results in sections of quadriceps, hamstrings, and strength.
Quadriceps
We already know that the leg press is a good exercise for developing the quads.2 However, depending on your foot placement, you might shift much of the work to your hip extensors (glutes and adductors).
The hack squat and the Smith machine squat, on the other hand, tend to be a bit more quad-focused with the standard exercise technique.
But the difference isn’t big, and in this case, it evidently didn’t make a statistically significant difference in terms of quad growth.
Hamstrings
The similar hamstring growth between the two groups is probably the part I least expected.
Previous research has shown that different exercises can activate different regions of the hamstrings. One study found that leg curls resulted in higher muscle activity in the lower hamstring region compared to stiff-legged deadlifts. In the high hamstring region (close to the hip), both exercises resulted in similar muscle activity.3
Another study found higher hamstring muscle activity from the Nordic hamstring curl and seated leg curl, than the stiff-leg deadlift, good morning, and back squat.4
Lastly, one study compared hamstring muscle growth from Nordic hamstring curls (with assistance) to stiff-legged deadlifts.5 Elite rugby players were assigned one of the exercises and trained twice weekly for five weeks. After five weeks, the biceps femoris thickness had increased by 8% in the Nordic hamstring group and only 4% in the stiff-leg deadlift group.
Moreover, the seated leg curl has previously been proven to be a very effective exercise for increasing thickness of the hamstring.6
Based on this, I would have expected the training program that included both seated and lying leg curls to outperform the program only containing stiff-leg deadlifts in terms of hamstring growth, but that wasn’t the case.
Now, this study only looked at muscle thickness and only on two sites; it’s possible that a MRI scan of the entire muscle length would tell another story.
Still, as far as this study goes, both training protocols were equally effective.
Strength
The strength outcomes were pretty much what I expected. Sure, I could imagine the slight extra quad focus from the other two quad exercises benefitting the non-trained leg extension a bit more. Still, we saw no statistically significant difference in this study.
The strength gain in the leg press is in line with what I would expect: Training a simple exercise like the leg press once a week is probably enough to get a high degree of proficiency in it, and then it doesn’t matter too much if you get the rest of your leg training from hack squats or Smith-machine squats; they’re quite similar movements.
Take-aways and Practical Recommendations
The main thing I think you should take away from this study is that if you select good exercises for your training program, you don’t seem to need a whole lot of variation to get great results.
Both the leg press and the stiff-legged deadlift are classic exercises that work many of your lower body muscles through a long range of motion in a stable and effective manner.
If you want more variation, that seems fine as well, and there might be benefits that weren’t covered in this particular study.
For lifters who want to get as strong as possible in specific lifts such as the squat, bench press, and deadlift, I believe this study strengthens the case that you can go two routes:
- Either the specialized route where most of your training is the lift itself, or
- The more varied route where the lift makes up some of your volume, but you also do a lot of accessory lifts that hit similar muscle groups.
Both seem like viable options.
The most important part is probably to pick a few decent exercises, and then train them hard and progressively.
For that, our app StrengthLog is a great tool.
It is completely free to track unlimited workouts in and has zero ads. There is a premium version with more features, but all your basic needs are met in the free version.
Download StrengthLog for free with the links below:
I hope you learned something from this article, and wish you the best of luck with your training!
More reading:
- Leg Press vs Squat: Which is Better For Muscle & Strength?
- Front Squat vs. Back Squat for Strength & Muscle Growth
- Smith Machine vs. Free Barbell Squats?
References
- Muscle Hypertrophy and Strength Adaptations to Systematically Varying Resistance Exercises. Kassiano, W., Costa, B., Kunevaliki, G., Nunes, J. P., Castro-e-Souza, P., de Paula Felipe, J., … Cyrino, E. S. (2024). Research Quarterly for Exercise and Sport, 1–11.
- Burke, R., Piñero, A., Mohan, A.E. et al. Exercise Selection Differentially Influences Lower Body Regional Muscle Development. J. of SCI. IN SPORT AND EXERCISE (2024).
- Regional differences in muscle activation during hamstrings exercise. J Strength Cond Res. 2015 Jan;29(1):159-64.
- Hamstring activation during lower body resistance training exercises. Int J Sports Physiol Perform. 2009 Mar;4(1):84-96.
- Muscular adaptations to training programs using the Nordic hamstring exercise or the stiff-leg deadlift in rugby players. Sport Sci Health (2021).
- Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths. Med Sci Sports Exerc. 2020 Oct 1.
