“Body fat is structurally important,” explains Stefanie Mendez, R.D., co-founder of Matriarch, a women's fitness and nutrition service. “It cushions our organs and insulates our body for temperature control and also is our body’s source of energy reserves. Beyond that, fat is needed for the production of hormones and reproduction functions.” And that fat can show up in your thighs, your belly, and, yes, your upper arms. Where it goes is partly due to genetics; if your mom has arm fat, science says you have a 62 percent chance of inheriting that trait.

What you can do is remove body fat from your entire body. Basically, you have to decrease your overall body fat composition if you want to lose weight from any specific place on your body. When you do that, you are going to eventually target the part of your body you want and you're going to lose body fat there. You can't just do 1000 push-ups every day and lose arm fat. Instead, you have to lose body fat in your entire body while building those arm muscles. You build up those muscles so that when your body fat percentage is low enough, they can show through.
The workout includes a dynamic warm-up to get your blood flowing and prep your body for the rest of the work ahead, and a cool-down to help you slow back down and wrap it all up. If you want to make the workout more challenging—maybe you've done it a handful of times and are ready to turn things up a notch—add weights to the lunge and squat movements. You can also, like Sims said, add another round of the main strength circuit.
McAlpine's favorite on-the-go exercise is a classic for a reason: Push-ups are one of the most effective bodyweight exercises around. "Primarily, this move will target your chest, triceps, and your anterior deltoid muscles (the front of your shoulders)," says McAlpine. It also seriously works your core. Plus, there's something that just feels badass about working on push-ups and seeing yourself improve over time. "I personally love that feeling of strength that comes from this simple move," says McAlpine.
Whether it’s a pick-up game of soccer, a group class at the gym, or just a run with a friend, exercise rarely happens in a bubble. And that’s good news for all of us. Studies show that most people perform better on aerobic tests when paired up with a workout buddy Aerobic exercise is promoted when individual performance affects the group: a test of the Kohler motivation gain effect. Irwin, B.C., Scorniaenchi, J., Kerr, N.L. et al. Kinesiology, Michigan State University, East Lansing, MI. Annals of Behavioral Medicine 2012;44(2):151-9.. Pin it to inspiration or good old-fashioned competition, nobody wants to let the other person down. In fact, being part of a team is so powerful that it can actually raise athletes’ tolerances for pain Rowers’ high: behavioural synchrony is correlated with elevated pain thresholds. Cohen EE, Ejsmond-Frey R, Knight N, Dunbar RI. Institute of Cognitive and Evolutionary Anthropology, University of Oxford, Oxford, UK. Biology Letters 2010 February 23;6(1):106-8.. Even fitness beginners can inspire each other to push harder during a sweat session, so find a workout buddy and get moving! Two-playered partner exergame for obesity prevention: using discrepancy in players’ abilities as a strategy to motivate physical activity. Feltz, D.L., Irwin, B., Kerr, N. Department of Kinesiology, Michigan State University, East Lansing, MI. Journal of Diabetes Science and Technology 2012; 6(4):820-7.
Harrison is also a hardcore burpee devotee. "It's a full-body exercise that will get your heart rate up, and it can be progressed and regressed in a variety of ways," she explains. (Psst—here are nine ways to do a burpee, no matter what your level is.) But her go-to burpee has a twist: "I also really love mountain climbers for some of the same reasons, so why not combine them?" The combo of the two will skyrocket your heart rate for a major cardio challenge.
If you struggle with a touch of fatigue, exercise might be just what the doctor ordered. According to a study from the University of Georgia, the blood flow benefits from exercise help carry oxygen and nutrients to muscles, which helps them produce more energy. They found that even low-to-moderate intensity exercise for just 20 minutes a day, three days a week for six weeks can help with that can't-keep-my-eyes-open feeling.
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.
Ever hit the hay after a long run or weight session at the gym? For some, a moderate workout can be the equivalent of a sleeping pill, even for people with insomnia Effects of moderate aerobic exercise training on chronic primary insomnia. Passos GS, Poyares D, Santana MG, D’Aurea CV, Youngstedt SD, Tufik S, de Mello MT. Department of Psychobiology, Universidade Federal de Sao Paulo, Sao Paulo, Brazil. Sleep Medicine. 2011 December;12(10):1018-27.. Moving around five to six hours before bedtime raises the body’s core temperature. When the body temp drops back to normal a few hours later, it signals the body that it’s time to sleep Effects of exercise on sleep. Youngstedt SD. Department of Exercise Science, Norman J. Arnold School of Public Health, University of South Carolina, Columbia, SC, USA. Clinical Sports Medicine. 2005 April;24(2):355-65..

Reduce your risk of heart diseases. Exercise strengthens your heart and improves your circulation. The increased blood flow raises the oxygen levels in your body. This helps lower your risk of heart diseases such as high cholesterol, coronary artery disease, and heart attack. Regular exercise can also lower your blood pressure and triglyceride levels.
Here's some quick physics fun: A body at rest tends to stay at rest. That's the fitness version of Newton's First Law, and it means that humans will find literally any excuse to not work out. I don't have time.... I felt a slight ache in my knee and don't want to make that worse... It's high tide. Somewhere. Probably. This happens to everyone—even the most dedicated, ruthless, disciplined gym-goers among us. (Like we said, it's science)
McAlpine's favorite on-the-go exercise is a classic for a reason: Push-ups are one of the most effective bodyweight exercises around. "Primarily, this move will target your chest, triceps, and your anterior deltoid muscles (the front of your shoulders)," says McAlpine. It also seriously works your core. Plus, there's something that just feels badass about working on push-ups and seeing yourself improve over time. "I personally love that feeling of strength that comes from this simple move," says McAlpine.
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