I have not had a transplant but my wife has. She had a double lung transplant a bit over four years ago. Regardless of what you read about organ transplants, they are a life-changing event. My wife's condition/transplant occupied both of us for five years pre-surgery and now the four years post surgery. She was a runner and hiker: she no longer is.
A transplant is not a simple procedure like replacing the brake pads on ones car. It is a process and has been likened to exchanging one disease for another.
My wife had pulmonary fibrosis which is a progressive scarring of lung tissue and is not related to smoking. My wife has never smoked. It starts with recurring bouts of pneumonia and difficulty with breathing. It then morphs into continual breathing issues. During this phase, one starts seeing a pulmonologist who works at diagnosis. Finally a surgical lung biopsy is ordered and the word comes down: pulmonary fibrosis, bronchiectisis and other associated issues. You then hear that you will be dead within 18 months baring a transplant. Heart, kidney and liver transplant candidates go through similar ordeals.
Qualifying for a transplant is another job of work. One undergoes a whole battery of tests and evaluative procedures including a psychological evaluation. If the proposed recipient makes it through all of the evaluations, then they are listed for a transplant. This basically means that you are waiting for someone who matches the tissue and size criteria to die. It's not a really good feeling! While you are waiting, you are required to constantly be within 2 hours of the hospital where surgery will be done; a really short leash. The recipient must also have a spouse or companion who provides support while waiting and after surgery.
Finally, the call comes. For us it was at 4:00 am on a Sunday morning. A quick shower, a few critical phone calls and you are off to the hospital. The recipient is prepped for surgery while the donor organs are being flown to the surgery hospital. The candidate is then rolled into the OR for the start of about ten hours of surgery not knowing for sure whether the donor organs will be acceptable; if not then the preliminary surgery is closed and it is back to the drawing board. For us, the donor lungs were good so the surgery went ahead. Ten hours later, she was in the ICU with tubes and wires everywhere.
Recovery from the surgery is prolonged. The recipient is on anti-bacterial and anti-viral drugs for several weeks with all sorts of side effects. There is also a strong initial course of anti-rejection drugs and drugs to regulate blood sugar and blood pressure. My wife spent nearly two months in the hospital post surgery.
Now, she is on a regimen of drugs that she will take for the rest of her life. Anti-rejection, steroids, beta blockers, potassium control drugs and a variety of nutritional supplements every day are the new rule. One of the lifetime drugs is Prograf, a strong anti-rejection drug that also causes slow, progressive kidney failure. And, she is in continual contact with the people in the transplant clinic. She has to have twice monthly blood tests and an annual comprehensive and overall medical evaluation including a pulmonary function test, x-Rays and a thoracic CAT scan.
All of this, the medications and continuous monitoring take a lot of time and attention and have many side-effects. There may be a few transplant patients who are backpacking or running marathons after surgery but in my experience, having been involved with a large transplant care-givers support group, there are not many. The pre-transplant debilitation and the stress of recovery from surgery take more from the patient than they are likely to ever regain.
So, from my perspective, someone who has undergone an organ transplant has enough to deal with in daily life without making plans to go backpacking. YMMV.