I think it's safe to say that most endurance athletes love physical activity. Certainly it would be difficult to train for a long-distance event if there wasn't a strong passion for working out. But with great enthusiasm to exercise comes a caveat - just because you are exercising, this doesn't mean you are becoming race ready.
Exercise (or physical activity) is commonly defined as anything that requires you to move your body and burn calories.
Training is viewed as working toward adequate levels of strength, endurance, speed and/or power for successful participation (and completion) of an athletic event.
To make the difference easier to understand, exercising satisfies an immediate need and is done for the effect is produces today. Exercise is done for its own sake - either during or immediately after. But when you have a specific performance objective in mind (ex. preparing for an event), you must change your physiology to prepare for the demands of your event.
Although all training is exercising, not all exercising is training.
Training is done with the purpose of achieving a long-term performance goal. Training is a process that must be planned out to produce specific results. It's methodically organized with great thought and understanding of human body.
Preparing for an endurance event requires a specific type of physiological adaptation. Every workout needs to have a purpose. Not all workouts require intervals or high intensity efforts but there needs to be a motive behind each workout in the plan. This is training. There's nothing wrong with working out with the primary objective of getting into shape, improving health or changing body composition, but if the primary purpose of the workout is to only burn calories or do what "feels right" on the day, this not only prevents performance improvements but it can also compromise health and emotional well-being.
The difference between exercising and training is how you approach the activity - not the activity itself.
Training requires intention, purpose and focus. It requires planning of nutrition, commitment to the task at hand and a smart mindset to listen to the body. If you want to improve your health, exercising will do just that. But you don't have to train for an Ironman distance triathlon or marathon to be healthy. And just because you train for an Ironman distance triathlon or marathon, this doesn't mean that you will remain healthy (or become healthier). Training requires putting your body under a specific type of intentional load, forcing it to adapt through training stress and recovery. Not always is this healthy. That is why training requires so much more than just checking off workouts for the sake of completing a certain number of training miles or hours.
Although endurance athletes are experiencing many changes to life, training and mental health during the pandemic, I do worry that many endurance athletes have turned into exceptional "exercisers." While it's great to stay physically active during a time of cancelled races, if you are seeking short or long-term performance improvements, there needs to be a systematic plan in place - with purpose and intent. Exercising your way through high volume, intense or random workouts will not give you the results that training can offer. More so, health can be compromised if you are not focused on the factors that can help your body safely adapt to training - like daily nutrition, sport nutrition, sleep, stress management, hydration and recovery.
Training takes work, it requires a committed mindset, it involves diligence with lifestyle habits (outside of training), results are not quick to achieve and it requires a certain amount of "embracing the grind."
But, with a structured plan and long-term goals in place, every training session provides an opportunity for growth and development.
And this is why training is fun - achieving a performance result when it truly matters, while also keeping the body in great health.