How to Stretch Your Knee
To stretch your knee, stand on one leg as you pull your other foot back towards your rear end. Hold the position for 30 seconds, and use a chair or a wall for support if you have poor balance. Then, repeat the stretch 2 to 4 times for each leg. Alternatively, sit on the ground with your legs straight out in front of you, and stretch your hands as far as you can towards your ankles for 20 seconds.
Use dynamic stretches to strengthen and stretch your muscles. By targeting the muscles surrounding your knee, you can relieve your stiff knee. Before you do dynamic stretches, you should get your blood pumping with a few range of motion activities. However, save your static stretches until you have completed your dynamic stretches. If you suspect an injury, be cautious in your range of motion and focus on strengthening the muscles more than stretching. Do 3 sets of 10 squats. This exercise works your thighs and supports good body mechanics - including how your knee moves - if it's done properly. Start with a smaller range or motion and keep your movements within your pain-free zone. Stand tall with your feet shoulder width apart, and rest your hands on your quads or extend your arms in front of you. Keep your back straight, bend your knees, and lower your hips as if you were sitting in a chair. Put your weight on your heels, hold the squat for 5 seconds, then bring yourself back into a standing position. When you bend your knees, keep them in line with your ankles and don't bend them past your toes. Letting your knee go past your ankle can hurt your knee worse. You can increase difficulty by adding hand weights or lifting one foot off the ground to do a single leg squat. Do 3 sets of hamstring curls per leg. Stand tall and hold the back of a chair or a wall for balance. Lift one foot back behind, keeping your knee pointing down and your thighs vertical and parallel to each other. Hold it for 5 seconds, lower your foot back to the ground, then repeat to complete a set of 10 repetitions. Do 3 sets of 10 curls for each leg. Do 2 sets of calf raises per leg. Hold the back of a chair or the wall for support, and raise your right foot slightly off the floor. Raise your left heel as high as you can so your toes support your weight. Hold it for 5 seconds, lower your heel to the ground, then repeat to complete a set of 10 lifts. If you have a step-up exercise platform or a stair, you could also work your calves by standing with your toes on the platform, then lowering your heels toward the floor. Do seated straight leg lifts. Sit up straight on the edge of a chair with your knees bent at 90 degree angles. Your thighs should be mostly off the seat. Raise and straighten your right leg as much as you can without causing pain in your knee and point your foot slightly outward. Engage your thigh muscles as you hold the position for 5 seconds. Bring your foot back to the floor, then repeat to complete a set of 10 lifts. Do 3 sets of 10 lifts per leg. Try 3 sets of dynamic lunges. Start by standing with your right leg out in front of you and your left leg behind you. You should step out as far as you can while remaining in your pain-free range of motion. Bend your knees and lower yourself into a lunge with your left knee pointing toward the floor, right thigh parallel with the floor, and your right foot firmly planted on the floor. Keep your weight on your right heel and push yourself back into the starting position. Keep your back straight throughout your lunge. Bend your knees in line with your feet, and don't bend your knee past your toes. Do 3 sets of 5 lunges per leg. Increase to sets of 10 reps when you feel ready. You can increase difficulty by doing walking lunges. Take a step each time you move in and out of the lunge position. Start with simple calf stretches. Stand in front of a wall with your left leg extended behind you and your right leg slightly bent at the knee. Place your hands flat against the wall with your elbows slightly bent. Keep your back leg straight and plant that heel on the floor as you push against the wall. You should feel a good stretch in your left calf. Hold the stretch for 20 to 30 seconds, then switch legs. Repeat the pose 2 to 4 times per leg. Do standing quadriceps stretches. Stand tall and engage your abdominals so you don't arch your back during the stretch. Bend your left knee back and bring your left foot around your rear end. Grab your left ankle with your left hand to gently bring your foot closer to your body. Push your left hip forward and tuck your tailbone under to increase the stretch. Your stretching knee should be pointing straight down or as close to straight as possible. If you have poor balance or flexibility, you can hold onto the wall or a chair for balance. You should feel a stretch in your quadriceps, or the front of your thigh. Hold the stretch for 20 to 30 seconds, switch legs, then repeat the stretch 2 to 4 times per leg. Open your hips with static lunge stretches. Start by kneeling on your left knee with your right knee bent at a 90-degree angle and your right foot planted flat on the floor. Alternatively, you could sit sideways with your hips turned in the chair. Tighten your glutes and raise your left arm straight in the air as you lean forward. Stretch your hips toward the floor as you lean, and hold the pose for 20 to 30 seconds. Switch sides, then repeat the stretch 2 to 4 times for leg. Do seated hamstring stretches. Sit on the floor with your back straight and both legs extended in front of you. Relax your knees slightly instead of locking them. Keep your feet neutral (instead of pointed or flexed) as you reach for your ankles. Try to keep your chest open and back straight instead of rounded and hunched. If you're flexible, touch your ankles or the soles of your feet. Otherwise, place your hands on the floor and slide them toward your feet as far as you can. Hold the stretch for 20 to 30 seconds, then repeat 2 to 4 times. This stretch can also be done by sitting on the edge of the seat of a chair, extending one leg at a time out in front of you, pointing the toes of the extended leg up to the sky and then hinging forward in the torso until you feel the pull down the back of the leg. Hold for 20-60 seconds, breathing deeply, and repeat with the other leg. Try a figure 4 stretch. Lie on your back with your knees bent, then bring your right ankle to your left quad just below your knee. Keeping your head and upper body on the floor, hold your left thigh with both hands and gently lift it toward your chest. Stop lifting when you feel a stretch in your glutes and hips, then hold the stretch for 20 to 30 seconds. Switch sides then repeat the stretch 2 to 4 times per leg. Warm up for at least 5 minutes before stretching. Getting your blood flowing before stretching can decrease the risk of injury. Aerobic activities like walking, running, or cycling are great warmups. Do range of motion activities and dynamic stretches before other exercises. Before you do conditioning exercises or a workout, get your blood pumping with range of motion exercises. Once your heart rate is up, do dynamic stretches. You can then perform your regular exercises or aerobic activity. When you finish your workout, do your static stretches. Static and dynamic stretches work differently and have unique benefits, so you should do both. Stretch regularly at work. Sitting in a chair or doing repetitive motions at work can be rough on your lower back, hips, and knees. You don't need to lie on the office floor to stretch. Try to find some time and space to do static quad, calf, and hamstring stretches. Dynamic stretches and conditioning exercises don't take much room, so you should be able to do them at work, too. Stretch after you run. Go for your run, then do static and dynamic stretches. Sticking to a post-run stretching routine can keep your knees from getting sore due to muscle tightness. Avoid stretching before you run, which can lead to strained muscles and lower performance. Talk to your doctor if you feel pain or have an injury. Avoid stretching if you're in pain or think you might have a strained muscle. If you're having knee issues, talk to your doctor or physical therapist before stretching or exercising. You should also consult a doctor before starting any exercise routine if you have a history of heart, bone, or joint issues. 
Use dynamic stretches to strengthen and stretch your muscles. Do 3 sets of 10 squats. Do 3 sets of hamstring curls per leg. Do 2 sets of calf raises per leg. Do seated straight leg lifts. Try 3 sets of dynamic lunges. Start with simple calf stretches. Do standing quadriceps stretches. Open your hips with static lunge stretches. Do seated hamstring stretches. Try a figure 4 stretch. Warm up for at least 5 minutes before stretching. Do range of motion activities and dynamic stretches before other exercises. Stretch regularly at work. Stretch after you run. Talk to your doctor if you feel pain or have an injury. 