Sorry if this feels like a slap in the face — I'm a personal trainer and I see many people with the same issue. Spinning, while a viable cardio supplement to strength training, can work against your fitness goals if it's your only source of exercise. Here’s why:
1. You will NOT see an increase in lean muscle mass.
At least not on your own body. Any (competent) fitness professional will tell you that cardio of any kind does not build muscle, and it never will. This basic, undisputable fact, applies to more than just spin class (e.g., most group fitness studios without weights), of course. Furthermore, excessive cardio can decrease lean muscle mass, regardless of how on point your nutrition is.
2. You won't experience a decrease in body fat.
Again, not happening, at least after the first couple of weeks, unless your class is supplementing with resistance-based training. Body-fat loss occurs when your body is challenged to the extent it needs to adapt and, since adaptation intrinsically needs to be continuous, settling into a consistent steady-state cardio routine will not only contribute to a plateau in weight loss, it can cause weight gain.
3. Sitting on a bike for an hour isn't doing your body any favors.
No one ever got a great butt by sitting on it. We spend nearly all of our waking hours on our iPhones, at a computer, behind the wheel, or generally reaching in front of our bodies for various reasons. These repetitive actions and positions reinforce damaging muscle imbalances in both our lower (e.g., tight quads and anterior hips) and upper (e.g., tight pecs, delts) bodies. When the front of your body is tight, you can bet the corresponding muscle groups in the back of your body (e.g., lats, glutes, hamstrings) are weak — both functionally and, as you may or may not have noticed in the mirror, aesthetically.
And you can forget about core activation: When’s the last time you admired your own six-pack (current or potential) while sitting down?
With all that said, I hope that you don’t throw your spin shoes away, but that you instead devise a balanced fitness routine for next week, like this:
Day 1: Take a strength-training class. A minimum (and maximum) of one hour, and be sure to select a studio that warms you up as well as focuses on mobility or at least static stretching at the end (a “cool down”).
Day 2: You will likely be tight and/or sore, so you have two options: a yoga or a flexibility-based class to work out the lactic acid or foam roll on your own before — and after — a cardio class. The worst thing you can do the day after lifting is to put yourself on a spin bike without remobilizing your lumbar spine and/or hip and shoulder complexes. The second worst is to do nothing.
Day 3: If your soreness has subsided (and this will become the case more readily the more you lift), feel free to repeat Day 1. Otherwise, this may be a rest day for you.
Day 4: Repeat either Day 1 or Day 2.
Day 5: Did you lift again yesterday? Guess what! Repeat Day 2. Was it a rest day? Great! Repeat Day 1.
Days 6 & 7: Starting to pick up on the pattern? My personal recommendation — particularly for those of us older than 30 — is to spend more time lifting weights than spinning or performing other cardio-centric activities (jogging/running, rowing, road/mountain biking, swimming, etc.), or approximately 3:2 (provided you take two rest days a week, which is recommended when beginning a new training regimen).
Here are some great strength-training workouts you can find on MBG: