The following set of yoga poses can be used as hamstring strengthening exercises. They work the hamstrings in a variety of different positions for developing all round hamstring strength. This may help improve hamstring flexibility.
The first exercise is extended cat pose.
While on all fours, reach one leg back with the knee straight and pointing downwards.
Pull the sacrum forwards (to arch the lower back) and then slowly lift the back leg higher.
This actually strengthens all the posterior chain if you focus on using the spinal erectors to bend the spine backwards and in addition use both the butt muscle and the hamstrings to lift the leg higher.
To activate the spinal erectors (and thus strengthen the "posterior chain"), start by lifting the sacrum so that your lower back arches. From there, bend your thoracic spine backwards also.
Make both actions active. So rather than sinking due to gravity, focus on feeling your spinal erectors activate.
Work at lifting slowly and hold for a breath or two then lower and do the other side, repeating both sides 5 or more times.
An option to add a balance component is to shift weight to the same side arm and leg so that you can lift the arm on the same side as the lifted leg.
A possible counterpose for extended leg cat pose is to tuck the toes under and lift the knees the knees off of the floor. Note, you only have to lift the knees a slight amount!
Bend your spine forwards.
For a fun challenge see how little you can lift the knees as an exercise in body awareness. Try for a 1mm lift.
You can use reverse plank as a hamstring strengthening exercise.
To begin with, start with your hands on the floor behind you and your legs straight. Press your heels down to activate your hamstrings. (Do this without allowing your hips to lift). Then, keep the hamstring (and glute) activation and lift your hips.
To begin with, try lifting your hips a slight amount while maintaining muscle activation. Then lower, and repeat.
Each time you repeat, you can work at lifting your hips gradually higher. As an added bonus exercise, try pointing your feet forwards.
While in a seated forward bend, with hands on the floor, allow your spine to round.
From there, open your chest. Press your legs down so that your arms relax. Then lift your hands.
Keep your legs "strong" and your chest open, reach your arms forwards. Make your spine feel long and make your arms feel long also. Reach forwards with your eyes.
Put your hands back down, and relax. Then repeat, lengthening and relaxing slowly and smoothly.
To turn table top into a hamstring strengthening exercise, sit with your hands on the floor behind you and with knees bent and feet flat on the floor.
Repeat a few times, noticing the feeling of increased pressure in your feet as you lift and also the increase in tension in your thighs.
Each repetition lift a little higher and as you do so retract your shoulder blades and reach your chest up (out of the shoulders) and back, away from the knees.
Hold for the final rep, looking for space to push your hips and ribcage higher.
Sitting with legs open wide to 90 degrees, bend forwards.
Position your hands in front of you but close to your pelvis so that they can easily support the weight of your ribcage.
Press your legs down so that your hands relax. Then lift your hands.
Hold, for a few breaths and then put your hands down and relax.
Once you are comfortable with your hands lifted (i.e. you feel safe) work at reaching the arms forwards slowly. With arms at full reach, make your spine feel long and make your arms feel long also.
Keep your legs feeling "strong" and reach forwards with your eyes.
Put your hands down to relax, and then repeat.
You can gradually tilt your pelvis forwards during the relaxation phase so that you stretch your hamstrings as well as strengthen them.
This hamstring strengthening exercise can be used in any forward bend where at least one leg is straight. (Press the knee down and then reach the arms forwards.)
You can use bridge pose as a glute or butt strengthening exercise. Because the knees are bent in this pose, it's a bit harder for the hamstrings to activate effectively.
While laying on your back with knees bent and feet flat on the floor:
To increase the workload in this butt astrengthening exercise:
A variation of the above hamstring strengthening exercise is to lay on the floor with legs straight.
Push the heels down to lift the hips.
You may have to walk the feet back slightly so that you have room to lift the hips off of the floor.
For both bridge options you can press the shoulders down into the floor and work at opening the front of your ribcage.
This hamstring strengthening exercise works the hamstring of the standing leg both on the way down and on the way up.
To begin with, balance on one foot with your standing knee straight.
Lift the other leg and pull the knee forwards slightly, allowing it to bend as you do so.
If you reach the lifted leg back, your hips will move forwards relative to the standing leg meaning that the hamstring of that leg does less work when you stand back up.
If you find strong pulling sensations or extremely strong lines of tension in your legs or hips, you need to adjust the way that you do the the above standing hamstring strengthening exercise.
It is a sign that something isn't working properly within your body.
And so the sensible thing to do is slow down.
Rather than trying to force yourself, notice what you do on the good side (hopefully one side is "good") and try to find the same feeling on the "not so good" side.
For more detailed instruction on feeling your body, in particular your hamstrings, check out the Hamstring Muscle control course.