Muscle imbalances are holding you back, so its time to address those imbalances, but first you need to test where they are.
A speed strength imbalance between two opposing muscle groups may be a limiting factor in the development of your speed. Muscle balance testing to compare the strength of opposing muscle groups is important to prevent injury and guarantee the maximum speed of muscle contraction and relaxation. Muscle imbalance can slow you down and result in injury.
Strength Checks
Leg press/body weight ratio
Your leg strength/body weight ratio indicates how easily you can get and keep your body moving at high speeds. This ratio is important to speed improvements in short distances. A good ratio is 2.5 times your "body weight". If it is less than 2.5 then you should consider modifying the program to develop leg strength.
Leg strength test
The squat is considered the most functional leg strength test in predicting sprinting and jumping ability. Good 1RM (one rep max) scores are:
Male athletes 2 × "Body Weight"
Female athletes 1.5 × "Body Weight"
Hamstring/Quadriceps strength
For each leg record the 1RM for the leg curl and leg extension exercises. Divide your leg curl score by the leg curl extension to find the ratio for each leg. For each leg, the curl score should be at least 80% of your extension score. If the score is less than 80% then you need to devote more training attention to the hamstrings. To reduce the chance of injury the ratio should be at least 75%.
Bench Press
This is a test for upper body strength. The need for maximum upper body strength varies between sports and so it does not always need to be tested for. Good 1RM scores are:
Male athletes 1.25 × "Body Weight"
Female athletes 0.8 × "Body Weight"
Balance checks
For each of the following exercises, the right and left limb 1RM scores should not differ by more than 10%.
Hamstrings (leg extension)
Quadriceps (leg curl)
Arm Curl
One arm military press
Single leg press
Where there is an imbalance then you need to devote more training attention to the muscle group of the weaker limb.