If you're still doing crunches and sit ups to achieve that six-pack, you could be wasting your time. Fitness experts say that it's important to strengthen your core muscles with a variety of isometric exercises that encourage deep muscle contractions in your abs and obliques, and these can help to improve your posture while giving you a killer workout. If you need to ramp up your ab routine, here are some essential exercises for a svelte midsection:

Oblique Twists
Oblique twists, also known as oblique crunches, are better than the standard crunch because they target the core muscles around your waist. You will need to perform these on both the right and left sides, and hold for a count of two to five seconds depending on your strength level. These exercises are among the easiest and most effective ways to achieve that streamlined midsection.

Renegade Rows
This routine involves lifting weights up off the floor while keeping the body in a push-up position with feet spread apart. The idea is to keep the hips as stable as possible while contracting the biceps and triceps during the lift. You'll feel the contraction in your midsection and sides, and a few sets of these each week can help you get those rock-solid abs you crave.

Planks
Plank routines, also known as hover exercises help build strength and stability in your core muscle groups and will also elongate your midsection. These can be performed on a workout mat with your forearms and toes on the floor. Your torso needs to be straight and rigid, and you will need to raise yourself up on your elbows slowly for a count of 10, 20 or 30 seconds depending on your strength level.

Medicine Ball Sit Ups
If you like doing sit ups but want to get better results, use a medicine ball. You can perform these crunches on a basic workout mat or yoga mat with or without shoes, and will need to hold at least a 5-pound ball between your legs and slowly lift it to your chest. The weight from the ball will encourage a deep contraction of your oblique and stomach muscles.

The late summer and early fall months are a great time to head outdoors for your fitness routine. But how do you make sure you're really getting in a great workout without the help of resistance equipment and mile-counters on the machines? Whether you choose to go swimming or head outside for a long jog, the heat may get to you faster than it would at the gym--which means you don't always know if you're pushing yourself hard enough. Here are ways to make the most of your workouts during late summer:

1. Wear the right clothing. Make sure your workout gear is well-suited for the weather or you risk dehydration and discomfort from the heat and humidity. You'll need lightweight, light-colored clothing made with moisture-wicking fabric so that your skin can breathe.

2. Throw on a visor. Pull your hair back in a ponytail if you have longer hair, and brush it back neatly if you have shorter hair so that you can wear a visor comfortably. A visor will help to block out the powerful sun rays of the late summer months and help you stay focused.

3. Wear sunglasses. Your eyes need to be protected from damaging UV rays, so make sure you're wearing a pair of well-fitting sunglasses that cover the entire eye area. Wraparound sunglasses and oversized sunglasses that reach your eyebrows are your best bets for an outdoor workout.

4. Carry a pedometer. Keep track of the miles you've covered so you're not pushing yourself beyond your limit. Set a goal and monitor your heart rate at regular intervals throughout the session so you don't injure yourself in the heat.

5. Don't forget the water bottle! Nothing will make you tired more quickly than being dehydrated. When you're working out under the hot sun, you need to prevent dehydration, so take along a large water bottle and keep it topped off from a water fountain whenever possible.

Working out outdoors is a great way to make the most of the nice weather during the late summer months and enjoy a change of scenery. Make sure you're well-prepared for the climate and protect yourself with these essential tips...and don't forget the sunscreen!