Swimsuit season can be frustrating if your body isn't quite ready for a bikini. It's possible, however, to build an athletic physique by following a workout program designed to help you build muscle and burn fat. Increasing lean muscle helps fire up your metabolism and burns fat to give your body a more toned appearance. Building a bikini body in just 20 days isn't necessarily practical if you have a significant amount of weight to lose, but committing to exercise can have you on the beach looking leaner, tighter and healthier.

Strength Training

Strength or resistance training can build muscle and increase your metabolism so your body burns more calories, even at rest. Engage in strength-training workouts four days a week, and work opposing muscle groups on the same day. For example, train your chest and back on Monday, quadriceps, hamstrings, glutes and calves on Tuesday, biceps and triceps on Thursday and abs on Friday. Incorporate a variety of compound exercises into your workout that activate multiple muscle groups at the same time and burn more calories per movement, such as bench presses, lunges, squats, pushups, overhead shoulder press and triceps dips. Work out with moderate resistance and perform four sets of 12 to 15 repetitions of every exercise.

Aerobic Activity

Aerobic exercise increases your cardiovascular fitness and burns fat. Participate in an aerobic activity such as walking, jogging or biking for 40 to 50 minutes, five days a week. Exercise in your fat-burning zone, which is 70 percent to 80 percent of your maximum heart rate. Calculate your target heart rate by subtracting your age from 220 and multiplying the number by 0.70 or 0.80. Wear a heart rate monitor when engaging in aerobic exercise to track the pace of your workout.

Nutrition

A healthy diet plays an important part in providing fuel for your workouts. Lean proteins such as chicken, low-fat dairy foods, fish, lean cuts of steak, ground turkey and legumes can help your muscles repair between workouts. Complex carbohydrates such as whole grain bread, whole wheat pasta, brown rice, quinoa, oatmeal, bran cereal, vegetables and fruits can help increase your energy levels. Include healthy fats such as nuts, seeds, coconut oil, olive oil and avocado as additional fuel sources to help improve your heart's health. Avoid fast foods, frozen dinners, potato chips, crackers and packaged desserts.

Considerations

Consult your physician before starting your new workout plan and always take one day off from exercise to give your body a chance to recover from your workouts. Performing high-intensity workouts daily can lead to over-training and injury, which might make your workouts counterproductive. Track your progress by having a fitness professional take your weight, body fat and measurements weekly.