Hello there, as you have compared speed of strength gain between muscle and a tendon, so here I would like to let you know that these are not totally a different tissues.... tendons are a sheath of fibrous connective tissue which joins bone with the muscle, its major roll is to pull a bone in a direction of pull of muscle, that's it.... There is very little contraction happening at tendons when a muscle acts.... and muscles are a bunch of contracting connective tissues which has a major part in moving a joint.... even though the role of both the tissues are different, both of them can not act in absence of any of them.... so, whenever you go for strengthening exercises, actually you are strengthening your muscle, not directly the tendon... as muscle gains strength, the tendon of it is also going to gain an appropriate strength to pull a bone... however it will not be possible to strengthen a muscle or a tendon alone.... so, don't worry as you gain strength in muscle, your tendon is also going to gain an appropriate strength to fulfill its role.

Hello there. It's always advised that excercise be done in a way that the intensity is gradually increased so as to not cause any harm. You you lift heavy weights today all of a sudden, you may be able to do it, but you may also injure yourself and cause problems like muscle tear etc. Therefore my advice would be to take things gradually and build strength gradually. Remember that Rome wasn't built in a day. All the best. Regards