Resistance training, simply put, is weight-bearing exercise. We use it to induce conscious muscular contraction, for a variety of reasons.
It can be as simple as using your own bodyweight to provide resistance, or as complex as using 'external resistance', such as weights or machines.
But why do we exercise this way?
A Multitude Of Benefits
As a style of exercise, resistance training delivers benefits other styles (like cardio) can't.
Here's a quick list of some of the real-world benefits you're likely to see:
An increase in strength;
An increase in speed & power;
Improved/retained muscle mass;
Improved hypertrophy (or 'aesthetic');
Increased anaerobic (short-term/high intensity) stamina;
Better functional capabilities (your ability to lift, push, pull, etc);
Improved muscle co-ordination.
Because a regular routine of resistance training can increase muscle mass, it can therefore also increase our 'Basal Metabolic Rate' - the calories we burn at rest each day. In a similar way to high intensity cardio, resistance training can recruit calories for the repair and building of new muscle tissue for around 48 hours, post training.
If you have a body composition based goal (body fat reduction, recomping, increasing lean muscle), resistance training is like 'passive income': we get rewarded even when we aren't actively working. Bonus!
Resistance training also delivers some incredible benefits for the long-term. Think of these as 'under the hood' improvements - like fine tuning a car so it performs well, long after you've bought it:
Improved bone density is a hugely positive by-product of regular resistance training, helping ward off issues like osteoporosis, fractures and disability in later life;
More resilient ligaments and tendons;
Higher flexibility & balance, helping you stay more independent, the older you get;
Some studies have shown a reduction in cholesterol, improved heart health, decelerated (or prevented) cognitive decline, better pain management and better glucose management as a direct result of regular resistance training.
'But I Don't Want To Look Bulky'
Some people do worry that adding resistance training to their exercise regime may cause them to 'bulk out' and change their aesthetic in a way they don't want.
Safe to say, building muscle is a slow process. It takes months and years of careful dedication to your diet and training to bulk up and out naturally.
Anyone consuming in a calorie deficit (or in most cases, at maintenance calories), should not bulk up. By resistance training in this state, your body simply won't have the excess calories to add size.
If you find that you're adding size, it's extremely likely that you're consistently consuming in an overall calorie surplus - in which case, it's important to ensure that you are targeting your calories/macros correctly (and accurately!).
Passive vs Conscious Engagement
People at all levels are susceptible to injury when it comes to resistance training. It's unforgiving in that, if you engage with it passively, it'll likely result in physical damage that can really stall your progress.
It is, however, easy to avoid. Choosing exercises that you can perform well go a long way towards ensuring that you can progress with your training.
Turn passive engagement into conscious engagement: warm up properly, lift with good form on every rep, don't be unrealistic with your volumes & take care of your recovery (especially stretching, mobility and posture) in between training.
Resistance training delivers so many benefits, but you are putting your body through unaccustomed stress most of the time you do it. Look after it, and the benefits of resistance training will seep into other areas of your life: an improved mindset, more confidence and self-esteem, more motivation to make better food choices, better sleep (and insomnia reduction), reduced stress, more social time (if you train with others) and, if you view it this way: using physical fitness as a form of self care.