Answer :
I'd say rowing since it would mostly affect upper-body strength.
Rowing can help her to improve her muscular fitness. As long as the intensity is the same, then 20 minutes of rowing will burn the same number of calories as 20 minutes of walking or climbing strairs.
And if we talk about Deep Breathing, it is not engaging any muscles so obviously it can't help in any muscular fitness obiusly
What is the meaning of muscular fitness?
Muscle fitness means having muscles that can lift heavier objects or muscles that will work longer before becoming exhausted. Muscle fitness improves when a person does activities that build or maintain muscles (strength) or that increase how long a person can use his or her muscles (endurance).
How long should I row for to build muscle?
"Spend 40 to 60 minutes rowing at a tough intensity that you can maintain for the whole period. This is a great way to work on your pacing, and it also requires a great deal of mental strength to stay consistent and focused!” It can be helpful to work with a heart rate monitor for this kind of steady state session.
Learn more about Rowing (for Fitness) here
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