When we take a step back and look at the entirety of our training as it is mapped out day-to-day, week-to-week, we see a flow of workouts that is broken into various categories: interval sessions; recovery workouts; aerobic workouts; strength workouts; long workouts and days off. If you’re a regular visitor to the ORION Training Systems site or are following me on Twitter, then you know I am a proponent of putting each workout in a box and treating it as it is meant to be treated.
In general, endurance athletes, especially Masters athletes, tend to press too hard too often. Recovery between intervals is both too short and too hard; recovery workouts are most definitely done too hard (even if they don’t feel hard) and typically too long. Strict aerobic workouts turn into Tempo sessions and long workouts tend to become slug fests with other athletes, especially on the bike.
Just as interval sessions serve a purpose and help us become faster, long workouts too have their purpose. And, if we press them too hard, we defeat the purpose for which they exist. Long workouts are meant to stress the body in ways that our other workouts simply cannot. The physiological adaptations by settling in and going long are different than a shorter long workout where you press the effort or do some race simulations. Learning to spare glycogen while tapping into fat as a fuel source is an important adaptation which gets compromised when the pace gets lifted and greater recruitment of Type II muscle fibers occurs. The goal isn't to "go hard" every workout, but rather ensure that the various types of workouts you complete complement each other rather than become variations of the same type of workout.
You should absolutely be tired at the end of a long workout. Afterall, you just ran for 90min or longer, or biked for 4+ hours. However, you shouldn't be shattered. If you feel shattered, you went too hard. My rule of thumb is this: If after I get home, shower up and replenish with a meal and water, if going up a flight of stairs later in the day feels normal, then I aced the workout, my in-workout fueling/hydrating, and my post-workout recovery. If, on the other hand, I feel like I'm climbing Everest or in standing up I get a little light-headed, then either my workout was too hard, I didn't fuel/hydrate nearly enough during it, or both.
And this over-reaching has lasting effects. Pushing that hard creates latent fatigue that will rear it's ugly head in various forms for days to come. Some workouts will go off fine, but others will certainly suffer. And, if you couple that over-reaching with under-fueling/under-hydrating, the effects last even longer. You've scraped the bottom of the barrel, which is much easier to empty than it is to fill back up.
The best mentality you can take into a long workout is to just complete it. Set your ceiling at the top of your L2 zone and focus on settling in to a solid yet manageable aerobic effort. This is not LSD training. This is not a recommendation to keep your chain in the SCR and spin away the time. This is guidance to stimulate the systems long workouts are meant to stimulate, keep the ego in the box and allow yourself to become a more efficient, faster aerobic machine. The biggest limiter for endurance athletes is not their thresholds; it is their lack of aerobic efficiency. Think of it as putting a lawnmower engine in a Porsche. You may look good, but your body can't support you the way you need it to because you've gravitated toward pushing your limits every workout. Who wants that?