For individuals who put forth an effort to regularly engage in physical exercise, it can be vexing and perplexing when everyday tasks prove to be physically demanding. Case in point: You frequent the gym, but when you ascend the stairs at work, you find yourself completely breathless. If you’re exerting substantial effort at the gym, why does something so ordinary feel so arduous?

First and foremost, it’s important to understand that feeling breathless when you reach the top of the stairs is not a cause for alarm regarding your health. “If you’re in good condition but feel out of breath when traversing a few flights of stairs, don’t fret!” advises Jennifer Haythe, M.D., a cardiologist and co-director of Columbia University’s Women’s Heart Center located in the department of medicine. “You’re not alone. Ascending stairs entails a burst of activity and engages multiple muscles in your body. Your body requires a sudden surge in oxygen, hence heavy breathing is normal,” she explains. Phew.

Now that we have that clarified, here are some of the reasons why stairs can be so challenging even if you’re physically fit, as well as how you can alleviate that breathless sensation. (If you’re experiencing persistent tightness in your chest, here’s a possible explanation.)

You fail to warm up before ascending the stairs.

Think about it. When you engage in a workout session, it typically takes a few minutes to get things in motion, correct? “A standard 60-minute cardiovascular class, by design, incorporates a 7- to 10-minute warm-up that gradually elevates your heart rate and enhances blood circulation, effectively preparing your body for the forthcoming cardiovascular demand,” explains Jennifer Novak, C.S.C.S., a performance recovery coach and founder of PEAK Symmetry Performance Strategies. When you bound up the stairs, you neglect to engage in any preparatory exercises to warm up beforehand. Consequently, instead of gradually elevating your heart rate and increasing your oxygen requirements, you’re suddenly exerting yourself, which presents a greater challenge for your body.

Stairs activate numerous muscle groups.

“My runners consistently inquire why they can successfully complete a marathon but find themselves breathless after ascending just one flight of stairs,” shares Meghan Kennihan, a NASM-certified personal trainer and USATF run coach.

Simply stated, it’s because ascending stairs requires a significant amount of your muscles. “Ascending a set of stairs engages more muscles compared to walking,” clarifies Kennihan. “Essentially, you are performing uphill lunges and battling against the force of gravity. If you are already engaging in intense physical training for a challenging event such as a triathlon or a marathon, then maneuvering up a flight of stairs only adds to your demanding workload, prompting your legs and respiratory system to provide feedback,” she observes. (Is anyone else going to refer to it as “performing uphill lunges” instead of “ascending stairs” from now on?)

Stairs necessitate a distinct form of energy.

Ascending stairs also utilizes a different energy system than typical aerobic exercise, which can render it considerably more challenging, asserts Novak. “The phosphagen energy system is what the body employs for rapid bursts of power and for brief episodes lasting under 30 seconds. The molecules employed to supply the energy for this variety of physical activity (referred to as creatine phosphate) are in limited reserve,” she clarifies. That implies that you possess diminished energy for abrupt spurts compared to what you possess for steady-state cardiovascular exercise, therefore, the fact that you experience fatigue more rapidly is not at all surprising when you acknowledge the source of the energy. (If you desire to specifically train stairs, attempt these stair-climber exercises from Blogilates creator Cassey Ho.)

TL;DR: There exist superior indicators of your physical fitness.

The essential point? You will probably always experience at least a bit of fatigue ascending stairs in your daily life, and it does not signify anything significant regarding your level of fitness. What is more meaningful, according to experts, is the duration it takes for you to recover. The fitter you are, the shorter the time it will require for your body to revert to its normal state after expending energy. “As you enhance both cardiovascular muscle and skeletal muscle through exercise, you will observe a reduction in your heart rate recovery time,” states Kennihan. “Your heart becomes more efficient, and your muscles acquire an increased supply of oxygenated blood with each contraction, thus your heart does not necessitate as much effort. As you augment the duration and intensity of your workouts, it translates to a healthier heart during periods when you are not exercising,” she adds.

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