As a high school runner, high-performance coach Mr Steve Magness pushed himself so hard in races that he invariably puked – until the time when his throat involuntarily closed (paradoxical vocal cord dysfunction, a protective mechanism gone haywire due to stress) and he collapsed. Rather than run faster by pushing relentlessly, he was forced to learn to relax.

That painful lesson was, “in many ways”, the start of Magness’ new book Do Hard Things: Why We Get Resilience Wrong and the Surprising Science of Real Toughness. Tied to masculinity and an “ethos of machismo”, the “glitzy Instagram-filter version” of toughness we’ve fallen for is, he writes, a fake one “developed through fear, fuelled by insecurity and based on appearance over substance”. The extreme workout with the goal of toughening us up is “alive and causing harm”. Hashtag go hard and go to hospital.

Dubbed a “miracle cure” for body and brain by the British Medical Journal, exercise nevertheless “isn’t helpful for everyone all the time”, according to the UK mental health charity Mind, which launched a campaign earlier this year about “developing a healthy relationship with physical activity”. A survey by Mind found that over a third of us use exercise to cope with difficult emotions, and almost half feel guilty when we miss it. Over-exercising (too long or intensely for your individual limits) and exercise addiction (feeling unable to control the amount, or to stop) are especially insidious because furious “fitness-ing” is widely, uncritically regarded as a good thing, a personal responsibility, a civic duty, a moral imperative, a heroic act, an aspirational lifestyle.

The difference between medicine and poison is the dose, and how you take it. This prescription will help ensure your relationship with exercise stays healthy – and happy.

“…And the kind of exercise you think fits you,” says Mr George Mycock, who founded mental health organisation MyoMinds after experiencing disordered eating and muscle dysmorphia: a pathological preoccupation that you’re not sufficiently big or lean. “Just because you play rugby doesn’t mean you can’t take part in a session of yoga,” he says. “In fact, it’ll probably be good for recovery and relaxation.”

Nor, Mycock points out, does exercise have to take place in a gym or studio: indeed, walking outside has been shown to make study subjects less tense and depressed, whereas walking on a treadmill didn’t. That said, exercising indoors has been shown to result in better mood and greater relaxation than sitting around doing nothing or playing on a computer. Al fresco walkers also tend to go faster yet find the exertion easier.

The word “exercise” can call to mind something planned, structured, goal-oriented, pressured, a workout. But being physically active doesn’t have to involve lifting weights or playing sport, and it doesn’t always have to be about getting fitter, stronger or more jacked. It can be anything that involves movement: yoga, walking, rock-climbing, dancing or taking your offspring to a trampoline park. (Actually, that last one is a workout.)

What committed exercisers of various, mostly outdoor disciplines wryly designate as “type two” fun – that is, not fun until it’s over, like climbing a gnarly route or running an ultramarathon – can be hugely rewarding. And exercise-induced pain can actually amplify our subsequent pleasure more than if we’d never had the pain via what psychologists call an “opponent process”, whereby a negative experience gives way to relief that itself gives pleasure. With repetition, that pain decreases over time, but the pleasure becomes stronger.

In the context of exercise, suffering is “a matter of perspective” to Mr Andrew Tracey, fitness editor of the Men’s Health UK. A narrative of suffering can help you endure, he says, but can also become another obstacle to conquer: either way, suffering isn’t, in his opinion, necessary. He strives to “find the ‘fun’ in functional” (training), and even in the several 24-hour charity workouts he’s completed: “Remember how privileged you are to be choosing to do this.”

And why actively choose to be miserable? Unless you’re a professional athlete, says Mycock, your guiding principle in exercise selection should be enjoyment, which will also help you remain consistent. Resentment, hate or dread is a red flag that you’re doing something wrong.

The philosophical “paradox of hedonism” is that you can’t pursue happiness: the disappointment of not yet reaching a goal, which can spur you on towards it, in this case makes you less happy, and so further away. The route to happiness is indirect, via things that aren’t pleasurable but are rewarding (meaningful work, type two fun, parenting).

Goals, exercise-related or otherwise, can by their nature can set us up for disappointment, because now we’re not where we want to be. That doesn’t mean we shouldn’t set them, says Dr Charlotte Markey, professor of psychology and health sciences at Rutgers University at Camden, New Jersey, and goals can be rewarding in themselves: “Of course, goals we achieve are more rewarding than ones we don’t.” Setting small, achievable goals – then, when you achieve them, new ones – keeps the process fun.

While we’re often told to shoot for the moon, writes Magness, that leads to demotivation: instead, we should aim just beyond our current capabilities. We’re also more likely to achieve “authentic” goals that reflect who we are and what we care about than ones imposed on us by others’ values. And “process-oriented” goals – giving your best effort, executing your gameplan – give more feedback for further growth, and succour, than narrower definitions of success as, say, winning or hitting a certain time. Improving your best average from your five most recent performances is also a “still tricky but achievable goal”.

We’re also often told that there’s no gain without pain, and certainly some discomfort or stress is a prerequisite for adaptation. But sometimes pain is a signal to stop.

Feelings and emotions are, writes Magness, like the instruments in a plane’s cockpit – but without labels. Rather than simply ignore potential warning lights, tougher athletes are those who can correctly interpret feedback and course-adjust accordingly.

“‘Listen to your body’ is great advice,” says Tracey. “But you have to learn to speak the language.” You can feel tired from too much exercise or too little; pushing through can sometimes lead to increased energy and progression, sometimes burnout and injury. Only you can decipher, with practice. (Your wearable tech doesn’t really know.) But unless your income is contingent on a rigid training regime, he says, skipping a session shouldn’t cause anguish: “The minute I feel anxious about missing a workout, I know it’s time to back off and reprioritise.”

The definition of rest is also individual. If doing nothing doesn’t sit easy with you, try “active rest”, which Mind’s guidance defines as “light or easy activity where you’re still moving, but not at a high intensity”. That could mean low-impact movements. (Tracey suggests sled pushes and loaded carries.) Or it could mean walking, yoga or secular stretching.

Training hard every day, or multiple times a day, and not taking breaks when you’re tired, injured or unwell, are symptoms that your relationship with exercise is unhealthy. And as in the title of Magness’ sustainable performance platform The Growth Equation, growth equals stress plus rest. Balance them with a Rate of Perceived Exertion scale, a tool used in elite sport (and helpful, says Magness’ collaborator Mr Brad Stulberg, for all life’s endeavours). Assess your effort on a scale of one to 10, and after a nine or 10 day, or a run of consecutive six-eight days, dial it down to one to three.

If exercise feels like something you can’t miss, or the most important thing, who you are, to the detriment of work, other relationships or the rest of your life generally, then that’s also unhealthy.

Exercise can bolster self-esteem, but as a main or sole foundation is dangerously fragile. The “hardcore” fitness mentality with which Tracey used to identify is “a house of sand that can very easily start to crumble the first few times you hit failure and that becomes ‘who you are’”. He still takes on challenges but prepares thoroughly, takes them one rep at a time and tries to not be too attached to the ultimately uncontrollable outcomes.

“Build your self-esteem on multiple different aspects of your being,” says Mycock. “This will help take the pressure off exercise, as it’s no longer the only thing you lean on.” Recently, he felt that he should go to the gym regardless of the heatwave and having not been well. But he noticed that sense of obligation and decided not to – and that was OK: “There are plenty of things that I value in my life that don’t revolve around exercise and I can delve into them instead.” Why do you feel you have to exercise? Would anything really bad really happen if you didn’t this once? This week?

Sometimes the hard – but beneficial – thing to do is cut yourself some slack.