Just about every athlete and weekend warrior relies on strong hamstrings. These muscles are responsible for bending your knees. If they're strong, you can jump high, run fast and accelerate with explosive power. With well-developed hamstrings, you can maintain good posture and prevent leg injuries.
The hamstrings consist of three main muscles that extend from your sit-bones to your knees: the biceps femoris, the semitendinosus and the semimembranosus.

Key Functions
Because your hamstrings cross the knee and hip joints, they bend your knees and draw your hips backwards. Your hamstrings contribute to functional motion, such as walking, and they help you to achieve speed, power and agility in many sports. When executing explosive movement, these muscles play an important part in shifting the load from your knees to your hips. For example, a sprinter's ability to launch off the blocks and accumulate speed depends on strong hamstrings.
They also contribute to your ability to absorb the shock of movements involving high velocity or force.

Deceleration
During the course of a contraction, your hamstrings shorten and lengthen. The concentric, or shortening, phase of a muscular action allows you to bend your knee, the eccentric phase, or lengthening, of the muscle helps you to control the deceleration of your body.

For example, when you're running downhill, the lengthening of your hamstrings helps you to control the speed of the descent. This ability to properly decelerate lowers the amount of pressure on the joints in your lower body and prevents injury.

Posture and Alignment

Strong hamstrings work to stabilize your hips and keep your spine properly aligned. Envision your skeletal system as a connected chain; if one link moves out of alignment, problems ripple through the chain.
If your hamstrings are weak and tight, they'll tug on your hips -- tipping them forward -- and compromise functional movement. A swayback posture, in which your lower back arches, and shoulders round may result.  

Your hamstrings also keep your knee and surrounding connective tissue in alignment.

If there's one fitness myth that just won't die, it's this one: Lifting weights makes women bulky. Full stop! Women will not "bulk up" if they lift weights -- even heavy ones! People often use the term "bulky" in a negative way to describe others, typically women, who have large muscles or well-defined physiques.

As weightlifting gained popularity and edged its way into mainstream culture, many women developed a fear of turning into Arnold Schwarzenegger if they so much as touched a 10-pound dumbbell.

Marketing masterminds caught on and someone, somewhere invented the terms "lean muscle" and "tone up" to target women who wanted to exercise but not get "buff." 

We need to nix all of these terms from the fitness vernacular because first, women won't bulk up if they start lifting weights; second, lifting weights produces so many health benefits; and third, it's blatantly sexist to think women shouldn't look muscular anyway.

​Here are four reasons to stop believing that strength training makes women bulky, plus several reasons to add weightlifting to your workout routine stat. 

It's actually insanely hard to build muscle

This is good news for some, bad news for others -- it's great news for women who are afraid of packing on too much muscle. Building muscle is a long, slow process that requires years of consistency, dedication and effort. 

Most people don't put in enough time or effort to create the kinds of physiques they're scared of. It takes several years to put on the kind of mass that bodybuilders have, and there's a reason professional bodybuilders are an elite few: They put in work that most people won't.

Women don't have enough testosterone to get bulky

In general, women don't produce as much testosterone as men. Testosterone production is a huge factor in your capacity for muscle growth, so this should automatically tell you that you won't turn into Wolverine overnight. 

Of course, there are always exceptions: Some women have higher testosterone levels than other women, but even those with higher-than-average testosterone likely don't have enough to produce bulky muscles. 

Many women don't eat enough to build big muscles

To build muscle, you must eat more calories than you burn. You can't grow new tissue out of nothing, so don't expect muscle growth if you're eating in a calorie deficit or even at maintenance. Many women don't eat enough calories or enough protein to support significant muscle growth. 

For reference, the recommended calorie intake for a healthy woman is between 1,800 and 2,400 calories. If you exercise, you probably need to meet the higher end of that range, and potentially more if you're tall or very active. Unless you're eating more than your maintenance intake each day, don't worry about getting bulky. 

Many women don't lift heavy (or often) enough to get bulky

Muscles don't grow in response to tasks they're used to. Your muscles need a challenge: If you're not progressively overloading your lifts on a regular basis, you're not encouraging your muscles to grow. They have no reason to get bigger if there is no demand. 

To add more muscle mass, you need follow two primary rules with your workouts: 

• Lift in the correct rep range (eight to 15 reps per set)
• Lift until you reach fatigue

What's more is that those two techniques only work for so long -- eventually, as you get stronger, you'll also need to add in techniques like drop sets, super sets, pyramid sets and repping to failure to send stronger muscle-building signals to your brain. 

Frequency is another key factor in building muscle. Studies show that when you train a muscle more often, it grows more in a shorter period of time. As with volume, however, there are caps on this concept. The stronger and fitter you get, the less of an impact frequency has on muscle growth.

Why women should lift weights 

Women won't bulk up when they start lifting weights. What they will do, though, is lose body fat and earn the "toned" appearance so many people are after. Beyond aesthetics, women who lift weights will experience the numerous health benefits of resistance training. 

Lifting weights can:

• Improve your bone density and help prevent osteoporosis, a degenerative bone disease common in older women
• Aid in weight loss (if you want to lose weight)
• Improve your body composition (increase lean mass and reduce fat mass)
• Reduce your risk of chronic diseases
• Benefit your mental health 
• Improve your flexibility and mobility
• Make you feel strong, empowered and confident 

If those reasons aren't enough to pick up a pair of dumbbells and start strength training, I don't know what is. 

Strength training is an important part of an overall fitness program. Here's what strength training can do for you — and how to get started.

Want to reduce body fat, increase lean muscle mass and burn calories more efficiently? Strength training to the rescue! Strength training is a key component of overall health and fitness for everyone.
Use it or lose itLean muscle mass naturally diminishes with age.
Your body fat percentage will increase over time if you don't do anything to replace the lean muscle you lose over time. Strength training can help you preserve and enhance your muscle mass at any age.
Strength training may also help you:

• Develop strong bones. By stressing your bones, strength training can increase bone density and reduce the risk of osteoporosis.
• Manage your weight. Strength training can help you manage or lose weight, and it can increase your metabolism to help you burn more calories.
• Enhance your quality of life. Strength training may enhance your quality of life and improve your ability to do everyday activities. Strength training can also protect your joints from injury. Building muscle also can contribute to better balance and may reduce your risk of falls. This can help you maintain independence as you age.
• Manage chronic conditions. Strength training can reduce the signs and symptoms of many chronic conditions, such as arthritis, back pain, obesity, heart disease, depression and diabetes.
• Sharpen your thinking skills. Some research suggests that regular strength training and aerobic exercise may help improve thinking and learning skills for older adults.

Consider the optionsStrength training can be done at home or in the gym. Common choices may include:

• Body weight. You can do many exercises with little or no equipment. Try pushups, pullups, planks, lunges and squats.
• Resistance tubing. Resistance tubing is inexpensive, lightweight tubing that provides resistance when stretched. You can choose from many types of resistance tubes in nearly any sporting goods store or online.
• Free weights. Barbells and dumbbells are classic strength training tools. If you don't have weights at home, you can use soup cans. Other options can include using medicine balls or kettle bells.
• Weight machines. Most fitness centers offer various resistance machines. You can invest in weight machines for use at home, too.
• Cable suspension training. Cable suspension training is another option to try. In cable suspension training, you suspend part of your body — such as your legs — while doing body weight training such as pushups or planks.

Getting startedIf you have a chronic condition, or if you're older than age 40 and you haven't been active recently, check with your doctor before beginning a strength training or aerobic fitness program.
Before beginning strength training, consider warming up with brisk walking or another aerobic activity for five or 10 minutes. Cold muscles are more prone to injury than are warm muscles.
Choose a weight or resistance level heavy enough to tire your muscles after about 12 to 15 repetitions. When you can easily do more repetitions of a certain exercise, gradually increase the weight or resistance.
Research shows that a single set of 12 to 15 repetitions with the proper weight can build muscle efficiently in most people and can be as effective as three sets of the same exercise. As long as you take the muscle you are working to fatigue — meaning you can't lift another repetition — you are doing the work necessary to make the muscle stronger. And fatiguing at a higher number of repetitions means you likely are using a lighter weight, which will make it easier for you to control and maintain correct form.
To give your muscles time to recover, rest one full day between exercising each specific muscle group.
Also be careful to listen to your body. If a strength training exercise causes pain, stop the exercise. Consider trying a lower weight or trying it again in a few days.
It's important to use proper technique in strength training to avoid injuries. If you're new to strength training, work with a trainer or other fitness specialist to learn correct form and technique. Remember to breathe as you strength train.
When to expect resultsYou don't need to spend hours a day lifting weights to benefit from strength training. You can see significant improvement in your strength with just two or three 20- or 30-minute strength training sessions a week.
For most healthy adults, the Department of Health and Human Services recommends these exercise guidelines:

• Aerobic activity. Get at least 150 minutes of moderate aerobic activity or 75 minutes of vigorous aerobic activity a week, or a combination of moderate and vigorous activity. The guidelines suggest that you spread out this exercise during the course of a week. Greater amounts of exercise will provide even greater health benefits. But even small amounts of physical activity are helpful. Being active for short periods of time throughout the day can add up to provide health benefits.
• Strength training. Do strength training exercises for all major muscle groups at least two times a week. Aim to do a single set of each exercise, using a weight or resistance level heavy enough to tire your muscles after about 12 to 15 repetitions.

As you incorporate strength training exercises into your fitness routine, you may notice improvement in your strength over time. As your muscle mass increases, you'll likely be able to lift weight more easily and for longer periods of time. If you keep it up, you can continue to increase your strength, even if you're not in shape when you begin.