"If you're capable of sending a legible text message between sets, you probably aren't working hard enough." - Dave Tate
As trainers, we all love that client who comes to the gym full of motivation and ready to get after it. You train him a few times a week and get him set up for programming and nutrition.
But there's a downside to this workout enthusiasm: you carefully plan his program, and in his spare time, he adds in more workouts, more cardio, and all kinds of additional fitness classes, because he says,
"More is always better, right?"
This may be true of eating your vegetables, but we trainers know that the latest research says shorter, more intense workouts are actually better than more, longer workouts. But how do we convince our clients to work out less, with more intensity?
A lot of training clients are motivated and want to speed up their results, thinking that the best way to do that is to increase the volume of their training and the length of their sessions.
Here's what you need to communicate to that client:
Going all out, three to four times per week is a better option. The science supports it.
Click to view full infographic or here to download PDF and print for your clients.
The first step in convincing your clients that fewer, more intense workouts will get them better results is to be able to give them the science. Here's what we know:
Calorie burn from intense training causes increases in metabolism for up to 38 hours after the workout is over.
Studies show that when training with higher intensity, even for just 4 minutes, epinephrine is increased, which forces a higher amount of fat to be used as energy. And, both fat oxidation and caloric expenditure remain elevated after the intense 20-second intervals involved with this type of training.
EPOC, excess post-exercise oxygen consumption, or the amount of oxygen required to restore the body to its normal, resting level of metabolic function, is bumped up after performing shorter bouts of intense training or weight lifting. This means the body burns many more calories as compared to longer duration, less intense activity. 
Most people are not used to training intensely, but studies show most people enjoy intense workouts more than steady state cardio. 
The science is the first step in changing your client's mentality, but now you need to make it personal.
If your clients are training hard and want more gains, no matter what the cost, they might be doing extra training on their off days (when they really should be resting). Or they may be adding multiple sessions in a day, or performing longer cardio sessions than you recommended.
Although they might see some initial results from this, they will not be able to keep up with hours of workouts for more than a few months for several reasons:
The client does not have the time to spend two or more hours in the gym every day.
She will experience serious symptoms of overtraining, like fatigue, a motivation drop, delayed recovery, an elevated resting heart rate, and persistently sore muscles. [1,11]
Her willpower and motivation will fatigue over time since she is putting in all the hard work with fewer and fewer results.
The body is only going to change if the demands on it keep getting harder. Making a workout longer does not necessarily make it harder. You have to train with intensity to make a change.
Share the progressive overload principle with your clients:
For a muscle to grow, strength to be gained, or performance to increase, the body must be forced to adapt to a tension that is above and beyond what it has previously experienced.
Now that you have convinced your hard-working client to work hard in a different way, here are a few simple ways to add intensity to their workouts:
Add on 4 minutes of Tabata Training at the end of an upper body workout day. 
Finish out with 10 minutes of sprint intervals. For example, try a 15-second sprint followed by a 30 second recovery period and repeat for a total of ten minutes. 
Add in 100 bodyweight squats at the end of leg day.
If you have clients working around injuries, you can get creative with the high-intensity workouts. I have a client with a knee injury, so jumping is out of the question, but the rower is great for interval sprints and is gentle on the knees.
The absolute best way to convince your clients to try shorter, more intense workouts is time. No one has enough time, and the most common excuse I know all trainers hear is:
"I'd love to get fit, but I just don't have time to work out."
Since high-intensity interval training has such stellar results and requires so little time, what's the excuse?
When you appeal to your client's sense of "not enough time," it becomes easier to talk her into a shorter, more intense workout that takes only 20 minutes, rather than subjecting her to an hour and a half workout.
People want quick fixes, and although HIIT still takes a great deal of work, clients report a better outcome since they don't feel like they are in the gym for hours.
Intensity directly correlates to results, and everyone needs to be training intensely - from the injured former athlete to the college girl looking to "tone" to the Silver Sneakers lady who's taking Zumba a few days a week. Results come from pushing the body to a new level, to go beyond the comfort zone.
As trainers, we also have a responsibility to keep our clients safe, so it is important to remind them that everyone's intensity level is different. Add intensity to your clients' workouts, but monitor them for signs they are overdoing it. Before you know it, each and every one of them will be on board with the new style of working harder, not longer.
Overreaching/Overtraining: More Is Not Always Better. ACSM'S Health & Fitness Journal: March/April 2015 - Volume 19 - Issue 2 - p 4-5 doi: 10.1249/FIT.0000000000000100
DEPARTMENTS: Fitness Focus
TABATA: Its a HIIT! Olson, Michele Ph.D., FACSM, CSCS ACSM'S Health & Fitness Journal: September/October 2014 - Volume 18 - Issue 5 - p 17-24 doi: 10.1249/FIT.
HIGH-INTENSITY INTERVAL TRAINING: A Review of Physiological and Psychological Responses. Kilpatrick, Marcus W.; Jung, Mary E.; Little, Jonathan P. ACSM'S Health & Fitness Journal: September/October 2014 - Volume 18 - Issue 5- p 11-16 doi: 10.1249/FIT.0000000000000067
Bartlett JD, Close GL, MacLaren DPM, Gregson W, Durst B, Morton JP. High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise: implications for exercise adherence. J Sport Sci. 2011; 29: 547-53.
Jung M, Little J. Taking a HIIT for physical activity: is interval training viable for improving health. In: Paper presented at the American College of Sports Medicine Annual Meeting: Indianapolis (IN). American College of Sports Medicine; 2013.
Martinez N. Perceptual responses to high-intensity interval training in overweight and sedentary individuals [thesis]. Tampa (FL): University of South Florida; 2013.
Exercise After-Brun: Research Update. Chantal A. Vella & Len Kravitz.
J Sports Sci. 2011 Mar;29(6):547-53. doi: 10.1080/02640414.2010.545427.
High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise: implications for exercise adherence. Barlett JD, Close GL, MacLaren DP, Gregson W, Drust B, Morton JP.
Schuenke, Mark; Mikat, Richard; McBride, Jeffrey (2002). "Effect of an acute period of resistance exercise on excess post-exercise oxygen consumption: Implications for body mass management". European Journal of Applied Physiology. 86 (5): 411-7. doj:10.1007/s00421-001-0568-y. PMID 1188297.
High-intensity interval training for health and fitness: can less be more? Glenn A. Gaesser, Siddhartha S. Angadi
Journal of Applied Physiology Published 1 December 2011 Vol. 111 no. 6, 1540-1541 DOI: 10.1152/japplphysiol.01237.2011