Excluding gym instruments, best exercise to strengthen and make them look good and healthy?
Your thighs will benefit most from focusing on two separate muscle groups which will require separate exercises to target. These two groups are going to be your quadriceps ("quads") which are the four muscles on the front side of your thigh, and your hamstrings which are a group of muscles and tendons on the back side of your thigh. As a bonus, the glutes are often involved in many hamstring exercises. In order for your muscles to grow you should work them to (or close to) failure within a set, and 2-3 sets a day 2-3 times a week should be plenty to see results.
Best Exercises for Your Quads
- Pistol Squats: Because this exercise only utilizes one leg at a time, it can give your quads a good challenge and stimulus for growth. Easier variants include the "Bench Bottom Pistol Squat", and the "Levitation Squat".
- Split Squat Hops: This would be the more dynamic option for your quads. It will help to train for explosiveness more than shape.
Best Exercises for Your Hamstrings
- Glute Ham Raise: The only trick to doing this exercise without equipment is finding a way to anchor your ankles into place. Be it a friend, furniture, or whatever happens to be around, this will be your best bodyweight option for training your hamstrings.
- Slick Floor Bridge Curl: This one also comes with a catch, you'll need to find both a slick floor and be wearing socks. Otherwise, it's a very accessible exercise.
- Hip Bucks: These are a final option, though less challenging than the others. It should also be noted that these are also primarily a glute exercise, but the hamstrings are certainly worked here as well. You might try doing a single leg variation to make them to reach failure within a more appropriate range.
JustSniloc had a good answer, but let me expand on that.
First, if you want bigger looking thighs, you need to be targeting your glutes and hamstrings. Why glutes and hamstring and not quads? Well first, a lot of knee problems stem from weak hamstrings and underactive glutes, so you'd be injury proofing yourself as you age. Two, Glutes are the one of the largest muscle groups in the human body and developing that region on it's own will yield a larger looking set of thighs. Look at an American football player, some of the largest and athletic men in sports; They have massive thighs, but if you see them in shorts, it's hardly the quads that stick out. They have massive butts as well as hamstrings and because these muscle groups are so large and critical to performance, it overshadows the quads.
The pistol squat is good, however, before you can reap the size benefits, there is a huge learning curve to that movement.
Instead of pistol squats and split squat hops, I'd look into: - Reverse Lunge: this is a very knee friendly option and it's extremely easy to learn. This excercise will hammer your Glutes better than any squat or deadlift. You can do this for high volume. Maybe start with 3 sets of 10 (10 reps each leg) and work your way up to higher sets and reps. As you get better at these movement, you'll notice depending on how you lean forward on the way down, you can emphasize different parts of your thighs. - Walking Lunge: less knee friendly than the reverse lunge, but once you get the hang of it, it's a great variation so you don't get bored. - Bulgarian Split Squat: very similar to the reverse lunge, but works your glutes, hamstrings, and quads in a different manner with more stabilization. - Glute Ham Raise: as JustSnilloc mentioned, it's a PHENOMENAL movement, but you will need a partner. Look up 'Nordic Curl', it's the same movement but without machines. - Hip Thrusts: fantastic glute and hamstring builder. Start with the glute bridge and once you can perform 100 reps (3x33, 4x25, 2x50 many ways to get 100), i'd do single leg glute bridge and then once your proficient at that progress to the hip thrust the nto the single leg hip thrust. - Sliding Hamstring Curl (Slick Floor Bridge Curl): is phenominal and you can pickup the necessary equipment off amazon for less than $10
Remember, of the exercises listed, not one is better than the other. They're all good. If i were you, I'd pick 2-3 exercises and focus on progressing them. I'd shoot to get somewhere between 50-100 reps on an exercise. Once you've hit a wall or get bored pick another 2-3 and work on those for a few weeks. But always be shooting to beat old records. If the last time you did Reverse Lunge you got 100 reps and you visit that movement again weeks later, shoot for 110.
I'd pick one squatting type movement (Reverse Lunge, Walking Lunge, Bulgarian Split Squat) and one Glute and hamstring movement (Hamstring Curl, Nordic Curl, Hip Thrusts). Good luck