While some women worry about the size of their hips, belly or thighs, other women feel that they have fat arms. Do your arms look as tight and firm as you'd like them to? If they don't, you're not alone. Almost all women struggle with some degree of flabbiness in their upper body and some of us even spend hours at the gym trying to lose arm fat or flabbiness in the upper back. 
Love 'em or hate 'em, you can't talk about ultra-effective no-equipment exercises without mentioning burpees (especially when there's a push-up incorporated). "The burpee with push-up is a full-body exercise that works your core, arms, quads, glutes, and hamstrings," explains Harbison. "[They also] rapidly increase your heart rate, especially if you add an explosive jump at the end of the movement." Strength, check. Cardio, check.
You probably have a vague sense that exercise is good for you—and you’ve probably heard that it’s “healthy for the heart.” But if you’re like most people, that’s not enough motivation to get you to break a sweat with any regularity. As I report in the TIME cover story, “The Exercise Cure,” only 20% of Americans get the recommended 150 minutes of strength and cardiovascular physical activity per week, more than half of all baby boomers report doing no exercise whatsoever, and 80.2 million Americans over age 6 are entirely inactive.
Scientists don’t know exactly why exercise changes the structure and function of the brain, but it’s an area of active research. So far, they’ve found that exercise improves blood flow to the brain, feeding the growth of new blood vessels and even new brain cells, thanks to the protein BDNF (brain-derived neurotrophic factor). BDNF triggers the growth of new neurons and helps repair and protect brain cells from degeneration. It may also help people focus, according to recent research.
The skin also serves as a release point for heat. (See “Why Does My Face Turn Red When I Exercise?” for more on that.) When you exercise, your muscles generate a lot of heat, which you have to give up to the environment so your body temperature doesn’t get too high, Hackney says. The heat in the muscle transfers to the blood, which shuttles it to the skin; it can then escape into the atmosphere.
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