Sure, why wouldn’t they be? Is anyone completely objective? And what does objective mean, anyway? I don’t know, but it sure sounds like an impressive word.
There are almost infinite ways to train, just as there are almost infinite varieties of people. I don’t think it’s a stretch to say that anyone who becomes a trainer has certain favorite modes of exercise. After gaining proficiency in your favorite styles, the tendency is to choose the data that support one’s favorite method, and at the same time, choosing data that invalidate other forms of exercise that you don’t like.
I remember getting a therapeutic massage once from a woman who was quite competent, and also chatty in a New Age-y sort of manner. We were talking about exercise, and she launched into a monologue about how terrible any exercise with weights was, just horrible for your body. She didn’t provide any supporting data, and I didn’t feel the need to argue. At the same time, I wouldn’t say she was especially fit. My muscles do best with a lot of pressure when massaged, and I explained that to her. But it quickly became clear that her hands weren’t strong enough to manage that, so while she did on OK job, I never went back. So her exercise methods, if any, weren’t necessarily optimal, either. To be sure, it is possible to hurt yourself lifting weights if you don’t know what you’re doing, and weightlifting may feel terrible to some, especially those who have never been physically active. But for many, weight training may be extremely effective and very safe.
You’ll hear Pilates people make generalizations about how their way of exercise gives you smooth, supple muscles, and that weight training gives you big, bulky muscles that ew, look gross! You’ll hear big hardcore iron-pumping jocks say that all Pilates and Yoga is crap, and that weightlifting is the only right way to exercise, and that they’ll beat up anyone who disagrees. You’ll hear distance runners say that doing triathlons and marathons is the mark of a good athlete, we don’t want any tacky upper body development. Cyclists might say their method is best, after all, you get cardio fitness, and you get to wear space-age clothes with circus-like colors. You know, they’re all right, and yet they’re all wrong at the same time. Any of these exercise methods has benefits, yet no one method of exercise is right for everybody, nor will they necessarily cover all aspects of fitness. Whether or not your trainer will admit this is moot – and if they’re testosterone-poisoned, there will be no arguing with them in any case.
When I was a kid, I ran for distance. It was a sport that required no equipment to speak of, and I could do it without any coach or teammates, and could do it almost anywhere. I was quite successful at it, and one year I had the fasted time in my school in the half-mile. But now I don’t care for distance running that much. It’s too slow, I have to rely on decent weather (or spend lots of money on a health club), it doesn’t work my upper body, and I don’t want cars to cut me off and splash me head to toe with puddles. It’s also pretty tough on your joints – there’s a good possibility of over-use injuries if you’re doing a lot of mileage. I prefer to exercise my whole body really hard for short periods of time so that I have time for all the other things I do. I want to be very fit and strong for everyday life activities, and to have good physical proportions. So that gives you an idea of my own biases.
Yet distance running is very pleasurable to many. I do remember the nice feeling when you’re cruising along on a nice day or night, enjoying the wind rushing by. And no expensive health club membership or gear needed, except for your fancy sneakers. It’s sort of smooth and gradual, and this fits some people’s temperament better than some of the fast, wilder stuff that I personally enjoy.
So I wouldn’t hesitate at all to recommend distance running for those who like it, could benefit from it, and are up to it physically. And that’s only one example. I also am more interested in strength per se than in having giant bodybuilder-style muscles, but if someone is interested in that, hey, why not?
Even if there were one magic routine that was better than all others, there’s also the element of compliance. You have to actually do the exercise to make something happen. If the person won’t stick to it, you’re back to square one. So some exercise, even if less than optimal, may be better than none, and the person’s habits, tastes, and fitness level must be considered. If you buy a book or DVD of favorite celebrity athlete’s fave workout, you may find that you can’t do it, you don’t like doing it, or it doesn’t actually give you results. That may be because the celeb is assuming that the one good workout plan will work for everyone else. Or if they’re more cynical, they know that their workout won’t work for many, but they just want some cash.
Regarding biases, maybe it’s better to call them “preferences”, which has a nicer sound. And a good trainer will not force you to accomodate their own biases. There is an exception to this – if that trainer is a super-athlete in one area, he/she may always train people to do that one thing, and that’s fine. It just doesn’t fit your average trainee.
So ideally when you meet with a prospective trainer, you can have a conversation that will help develop a personalized program just for you. If you don’t communicate any preferences, interests, or useful background information, you may very well just get a canned exercise program.