Test of Strength: Fitness Apps vs. Personal Trainers

ACTIVITY trackers. Calorie counters. Phones with heart monitors.

Technology companies are clearly fascinated with fitness and health these days. As technology starts pushing us to be healthier and fitter, some apps are even trying to replace the personal trainer or the gym entirely.

The idea is pretty simple: While personal trainers can create a safe and effective workout, they can be expensive and sometimes inconvenient. A fitness app, though, can travel where you are and is relatively inexpensive — and sometimes even free.

So I spent the month of January on a personal fitness challenge, seeing what provided a better workout: a real personal trainer or a personal training app. And while the trainer pushed me hard and motivated me to keep my expensive appointments, I found that the app was best suited to my lifestyle and might have the most long-term potential.

Kiqplan is a workout plan sold in stores as a $20 gift card that unlocks a 12-week workout (choose from Slim and Trim, Beer Belly Blaster and others). The app includes nutrition coaching, integration with activity trackers and rewards for hitting certain milestones.

And Hot5 has a collection of high-intensity five-minute workouts that you combine into longer sessions, with nice videos that feature a variety of trainers. It’s $3 a month, or $22 a year.

But the best option I found was FitStar, a free personal trainer app. For $40 a year, you get access to more workouts. From the apps I tried, FitStar was the closest to using an actual trainer because it can build workouts customized to your fitness level and goals.

The workouts range from 10 to 50 minutes, and while some apps just have you repeat the same exercises over and over, FitStar mixes up the exercises as you go through its programs. The workouts gradually get harder, and you can rate each exercise individually as too easy, just right, or “brutal.”

So if you have strong legs, the app will quickly learn to work them really hard. And if your upper body is relatively weak, the app adjusts to work on those muscles, starting at a lower intensity level.

The founders of FitStar said they worked with exercise physiologists and personal trainers to come up with a baseline collection of workouts. And the app uses the anonymous data collected from all their users to adjust individual programs for each user.

“It’s not unlike video games where you have matchmaking systems for online play, and they can pair you up with opponents at your level,” said Mike Maser, a co-founder and the chief executive of FitStar. “We use similar algorithms to match you up with a workout that’s at your level but pushes you just enough.”

Mr. Maser said he believed “100 percent” that people could get themselves into shape using only FitStar, but he said the app could also be used alongside a personal trainer’s regimen.

FitStar is convenient and fun to use. Workout videos are hosted and narrated by the personable former N.F.L. player Tony Gonzalez and feature his wife and some other athletes. (FitStar also makes a yoga app hosted by Tara Stiles, a former model and YouTube yoga star.)

The app doesn’t require weights or other equipment, which makes it easy to use anywhere. It integrates with MyFitness Pal, which is my favorite app for tracking calorie intake. When you perform a workout, FitStar automatically sends the number of calories burned to MyFitness Pal, so you know how many more you can have that day.

I noticed the progression of the workouts over the course of the month. One downside, though, is that you can’t opt to change your fitness level after you start the program to make your workouts significantly harder or easier. If the exercises are not intense enough, you can only tell the app that the exercises were too easy, and the app slowly increases the intensity the next time. And the app can’t adjust workouts for injury — a problem for me, since I have a foot injury that limits range of motion.

By contrast, working with a trainer took me well out of my comfort zone, protected my injury and probably produced faster results. Like the apps, however, there are many types of trainers.

I had a personal recommendation to try Alison Roessler, who runs Truve, a private training and wellness center in Oakland, Calif. If you don’t have a recommendation that you trust, Ms. Roessler said, a key to finding a good trainer is to ask about their certifications and qualifications. Also, make sure the trainer evaluates your capabilities and injuries before you start.

Ms. Roessler, an athlete who was a runner and soccer player before she started Truve, has five nationally recognized training certifications. She charges $100 an hour for training sessions and said she tried to avoid repeating workouts.

Not surprisingly, the workouts with Ms. Roessler were much more difficult than the workouts with the app — probably because I underestimated my fitness ability when I filled in my FitStar profile. As a result, when my trainer pushed me to try more difficult workouts after just a few sessions, I felt a real sense of accomplishment.

FitStar didn’t push me as far, as fast. If you were starting from scratch and trying to get into shape with only FitStar, the results might be slow in coming, which could cause you to get frustrated and abandon the app.

However, convenience and price count for a lot, and in the long run, FitStar’s location-agnostic, bite-size workouts seem more feasible than a $100-an-hour standing appointment across town.

What is not included with FitStar, however, is motivation. Several fitness experts I talked to said that despite the success stories trumpeted on the back of fitness DVDs and on the FitStar blog, many people lack the motivation to achieve significant results from working out alone with an app or video.

“It’s easy to break an appointment with your TV, easy to break an appointment with your iPad,” said Michael Boyle, who trains professional athletes and others at a Boston-area strength and conditioning center and runs the blog StrengthCoach.com.

I skipped my workouts when I went on vacation. And long-term habits are hard to change, with or without technology — we know that more than a third of people abandon their fitness trackers after just a few months.

But personal trainers are simply out of reach for many people, either because of the cost or the rigid scheduling. However, Mr. Boyle said that small group classes had proved to be a popular alternative to both one-on-one training and at-home workouts. The classes combine social encouragement with the motivation of an appointment, as well as at least some financial penalty for skipping a workout.

So while FitStar might seem like the right solution to keep the endorphins high and the waistline shrinking, the real test won’t be one month — it’ll be two, three or four. Maybe by then I will have dumped both the trainer and the training app for a class at SoulCycle, the popular spinning studio, instead. Anything but the couch.