This is what we found on Wikipedia regarding the Personal Trainer:

A personal trainer is an individual who creates and delivers safe and effective exercise programs for healthy individuals and groups, or those with medical clearance to exercise. They motivate clients by collaborating to set goals, providing meaningful feedback, and by being a reliable source for accountability. Trainers also conduct a variety of assessments beginning with a preparticipation health-screening and may also include assessments of posture and movement, flexibility, balance, core function, cardio-respiratory fitness, muscular fitness, body composition, and skill-related parameters (e.g. power, agility, coordination, speed, and reactivity) to observe and gather relevant information needed to develop an effective exercise program and support client goal attainment.

These assessments may be performed at the beginning of and after an exercise program to measure client progress toward improved physical fitness. Trainers create exercise programs following a progression model, using the baseline assessment as the starting point of a client's physical abilities and framing the program to fit the individual personally. They also provide education on many other aspects of wellness, including general health and nutrition guidelines. Helping clients to reach their full potential in various aspects of life requires a comprehensive client-centered approach along with a belief that clients are resourceful and capable of change.

Qualified personal trainers or certified personal trainers (CPTs) recognize their own areas of expertise. If a trainer suspects that one of their clients has a medical condition that could prevent the client from safe participation in an exercise program, they must refer the client to the proper health professional for medical clearance.