The spin class doctors

When you've been away from a gym for a while, passing by one is like glancing back at an airplane cabin after a 17-hour flight. Nothing, it seems, will induce you back there, to the smells, the grey décor, the cold metal, the straps, the proximity to strangers.

Cardiovascular workouts in a gym are probably the most mind-numbing modern activity we know. One of the biggest selling points, discussed over post-workout smoothies, is how much the class "killed" you.

The more exhausted you are, the better it must have been. The more the buff, be-microphoned instructor yelled "Let's take it through the roof!" the more your body must be on its way to looking like his or hers.

Now, if you have a good base level of fitness, taper your regular workouts before the class, take a couple of days for recovery after, and really space these hard sessions out, it's likely that they will help you. For anyone else, "taking it through the roof" is the fastest way to come crashing back down to the floor.

Being exhausted at the end of a workout is not an indicator of its quality. When you have the flu, getting up and going to the bathroom is tiring, but doesn't make you fitter. A day at your office desk can be exhausting, as can that 17-hour flight — but neither has any health benefits I can think of.

For anyone contemplating these classes, it's important to understand that your body is just as stubborn as you are. If you're owed a week's holiday, you would never accept 14 half days, or alternate days off, would you?

Similarly, your body only responds to exercise if it's above a certain level for a minimum amount of time. Your heart rate must rise into the ‘training zone' for at least 30 minutes at least three times a week, before your shiftless corpse starts getting its rear in gear.

When you go too hard, you blaze through your carbohydrate stores and are soon left with too little energy to raise and sustain your heart rate in the training zone — the classic "my legs were like jelly".

You're wasting large portions of your workout and any gains you make will be for the short term, as you're training your body to favour precious carbohydrates over a near endless supply of fat. Too many of these depleting sessions and you'll burn out, with all the nasty symptoms of over-training. Never forget that health and fitness need not occur together in an individual.

Just as youth is wasted on the young, lack of fitness is wasted on the unfit. The fact that you don't have to work too hard to enter the training zone is a huge blessing. A brisk walk every evening after dinner is enough to start all the amazing changes that come with exercise — beautiful sleep, high energy, a positive outlook.

Enjoy it now, when you don't have to run for 20 minutes before your body even registers you're moving. Look into the gym and never forget that exercise should always be fun and nothing like a trans-Pacific flight in economy class.

Gautam Raja is a journalist based in the US.