around here isos tend to be recommended for muscle activation and not so much for tendon stuff. for that the go-to exercise seems to be negatives, where you do the concentric portion of an exercise assisted, and then remove one limb from the equation and do the eccentric portion. for example, for achilles/calf stuff, get into the starting position for a barbell calf raise, lift yourself up on both toes, then pick up your left leg and lower yourself using only the right. repeat etc. and then switch legs.
take all that with a grain of salt, it's just my own reading and experience, nothing professional.
