We love answering the questions we get from our readers via Twitter, Facebook, email, or carrier pigeon. We figure, if one person’s wondering, other people probably are, too. That’s why we’ve started Ask Greatist! Send us your questions anytime, about anything related to health, fitness, or happiness. We’ll answer two each week!

Mary G. (@marygrinton) via Twitter wants to know…

Which type of greens packs the most nutrients per bite?

We’re all about the greens. No, not dolla, dolla bills— leafy green vegetables! This group of veggies can include anything from cruciferous veggies to types of lettuce, to the leafy bits of other favorite veggies (beet or turnip tops, anyone?). Here, we’ll talk about two basic categories: salad greens and cooked greens.

The best greens for salad: While arugula and endive do offer a healthy dose of vitamins, they can’t beat their beefier competition. Romaine is probably the healthiest “traditional” salad green, but it still can’t compete with the more non-traditional spinach salad (OK, so it’s not that uncommon). Spinach provides well over the recommended daily value of vitamin K and plenty of vitamin A, folate, omega-3 fatty acids, and manganese. Plus, it offers more fiber and protein than it’s competition. And, it’s endorsed by Popeye— ‘nuff said.

The best greens for cooking: Sure, some salad contenders are great cooked, too. But if cooking is the method of choice, other options may be better. While mustard greens and Swiss chard both are still seriously stellar greens, they aren’t quite as rich in nutrients as other options for cooking. Overall, collards take the crown, offering more fiber, protein, calcium, and iron than both kale and turnip greens. All are also an excellent source of vitamins E, C, and K. Kale and collards even offer a whopping 1,000+ percent of the daily recommended dose of vitamin K. Talk about power-food!

*Note: all nutrition information in this section is for the greens boiled and without salt

Alex B. (@alexhbryant) via Twitter wants to know…

Which cardio machine at the gym is the best workout: treadmill, stationary bike, or elliptical?

First off, it’s important to remember both cardio and weight training are essential to a well-balanced fitness routine. That said, the answer to this question is a bit subjective. If getting that ticker pumping is the top priority, any of the machines you mention can be effective if used properly (no getting distracted by Rachael Ray or Sports Center on TV!). While not exact, the heart rate monitor featured on some cardio machines can give a ballpark range of how much blood pressure is increasing while using that particular machine The accuracy and reliability of commercial heart rate monitors. Burke, M.J., Whelan, M.V. British Journal of Sports Medicine. 1987 March; 21(1): 29-32. . Similarly, workout intensity on any machine can be altered to increase (or decrease) calorie burn. As a baseline, walking at 3.5 miles per hour burns about the same number of calories as a leisurely bike ride (think under 10 mph).

Elliptical machines with movable ski-pole-like handles might offer a bit more full-body training. On the other hand (err…foot?), the treadmill is tops for tightening up that tush. A jog on the treadmill is the most effective for targeting glutes, followed by the elliptical, a walk on the treadmill, and then the stationary bike. The treadmill is also clutch for anyone training for a running event (like, say, running a 5K). However, adding in cross-training on the elliptical and bike can help prevent injury or, heck, boredom. But beware— the high-impact of treadmills can cause joint troubles. The elliptical is typically a lower-impact alternative, while the bike offers the lowest-impact cardio.

So the real answer? It’s your call. Choose the machine that allows you to stay motivated and up calorie burn and heart rate. Unless, of course, you’re training for a specific event or are injured, in which case, you should defer to a doctor or trainer’s recommendations.

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