Bosu Ball exercises can be used to work certain muscles. Sometimes to a larger extent than the regular version of the exercises.
You can describe the Bosu Ball as the top of a stability ball attached to a flat surface. What muscles a Bosu Ball works depends on the Bosu Ball exercises you do with it.
For example, Bosu Ball crunches will mainly work your ab and oblique muscles. On the other hand, Bosu Ball squats will focus more on your quadriceps, glutes, hamstrings, and calves.
That being said, in general using a Bosu Ball often makes it so you work your core muscles, ankle muscles, and thigh muscles slightly more compared to doing the same exercise with the same resistance on a flat surface.
Something important to keep in mind is that this does not mean the Bosu Ball is always more effective for building muscle. Many exercises become less effective for muscle growth by adding a Bosu Ball.
This is because to grow and strengthen muscles you need to use enough resistance, often in the form of weights like for example a loaded barbell.
There are exceptions in the form of exercises for weaker muscles like core muscles. However, heavy weights usually do not combine well with a Bosu Ball because of the balance challenge and weight limit.
- Related: 7 Of The Best Bosu Balls Reviewed
One study compared the difference in core muscle activation between sit-ups on a flat surface, sit-ups with a Bosu Ball under their feet, sit-ups with a Bosu Ball under their lower back, and sit-ups with both a Bosu Ball under their feet and back.
Additionally, they measured these differences with just body weight and a 10 repetition maximum resistance.
They measured that in bodyweight sit-ups, external oblique muscle activation was decreased by both variations with the Bosu Ball under the lower back (1).
In the sit-ups with extra resistance, putting a Bosu Ball under the back of the participants lead to increased muscle activation in the upper and lower rectus abdominis.
In the sit-up versions with the Bosu Ball under the feet, they measured no significant differences compared to the flat surface sit-ups.
So if you like the difference in muscle engagement, you can do Bosu Ball sit-ups with the ball under your back.
The next study compared muscle activation during half back squats on a flat surface, foam surface, Bosu Ball up, and Bosu Ball down with the same weight.
They measured an increase in muscle activity in the vastus medialis, vastus lateralis, and biceps femoris (quadricep and hamstring muscles, aka front and back thighs) (2).
Another study again measured muscle activation in multiple leg muscles in both a floor squat and Bosu Ball squat.
This time they measured a significant increase in gastrocnemius (calves), biceps femoris (hamstring muscle), and quadriceps activity (3).
Keep in mind that these things do not mean Bosu Ball squats are better for muscle growth. To achieve muscle growth and strengthening you have to use enough weight during an exercise. You can squat a lot more weight on a flat surface.
Additionally, a different study measured a higher EMG activity in the rectus femoris in isometric squats on the floor compared to isometric squats on a Bosu Ball (4). They did not observe any significant differences in the other muscles measured.
Core muscles during compound lifts
A study measured the differences in muscle activity in a variety of core muscles during compound exercises like back squats, deadlifts, overhead presses, and curl lifts.
They measured this with 50% of a one-rep-max resistance on the Bosu Ball and 50% and 75% of a one-rep-max resistance on a stable surface.
They did not find any significant differences in core muscle engagement between the 50% 1-RM on the Bosu Ball vs on the ground (5).
As is somewhat expected, they did find an increase in activity of certain core muscles in the 75% 1-RM on the floor vs the 50% 1-RM on the Bosu Ball.
Erector spinae during deadlifts
The erector spinae are a group of muscles that help you keep your spine straight. One study measured the activity in these muscles while doing deadlifts with 70% of maximum isometric force on a flat surface vs doing deadlifts with the same resistance on a Bosu Ball.
They measured higher muscle activity in the erector spinae during the regular deadlifts on the floor (6). Unfortunately, the activity in other core muscles was not measured.