Good questions! Thanks. The answer to all of them is……..It Depends. So lets look at what they depend on:
1) HR will be lower but this varies by individual by a lot. Just like the amount of weight you need to carry or how steep the hill is to elicit the desired response depends upon how strong your legs are, the amount of drop in HR when you are doing these depends on how high your Max HR is and how much weight it takes to get the legs to be the limiter. There are a bunch of variables such that trying to give a standard percentage is not going to apply to everyone. For instance I was recently working with a fit professional climbing guide prepping for trip to Pakistan. His Max HR was over 200 and he had very strong legs. So, despite only weighing 140lbs it took several experimental tries and finally a 65lb pack to get his legs to become the limitation and even then his HR was 170-175 for 1 hour uphill ME water carries. This is why I have gone to some length in describing the sensation you are looking for in the workout. This is what you need to feel: Your legs need to be the limiter and not the breathing. You should be able to carry on a conversation while feeling a low grade sustainable burn in the legs. This is the best measure of whether you are doing this right.
2) Slow or fast twitch? Of course there is not black or white when it comes to fiber recruitment or fiber type but the theory behind these workouts is that by adding extra resistance you are forcing the recruitment of the most endurance limiting fibers for these sport specific movements and thereby improving those FT fibers endurance because the stay in the game for many minutes AND you should also be increasing the strength of the ST fiber pool which has adequate endurance already. This is the theory form strength training. In the endurance world we accomplish a similar training effect when we do Z4 intervals. Those workouts have a very strong muscular endurance component to them. But, they also have a very powerful cardiovascular effect as well and tend to be fatigue limited in duration by lactate accumulation. In fact, the cardio vascular system may not get adequate stimulus if the ME is too low: If the fibers begin to drop out of the recruitment pool due to lactate accumulation and the athlete slows, the cardiac demand drops and the heart doesn’t get the big stimulus we look for with Z4 intervals. With conventional athletes, like XC skiers, I do an ME phase before moving to lots of Z4 endurance intervals.
3) Lactate levels. Way too individual to predict. I’ve had Olympic level XC skiers whose lactate thresholds ranged from 3.5 mMol/L to 7mMol/L. So no way to answer this question. How good is the individual athlete’s lactate shuttling mechanism?
4) Working time of an ME session is related to the event. For an alpinist or mountaineer it can range from 1000 feet for someone new to this type of training up to 6000 feet for myself before K2 or Steve at his prime. David Roeske spent some ridiculous days in NYC stairwells https://www.uphillathlete.com/the-martian-trains-for-everest/. Again it is very individual. A high level climber with strong legs and a big aerobic base can handle a many thousands of feet. On the other hand a workout like this for an Olympic XC ski Sprinter would look very different than for a climber. The skier has to train at much higher speeds, higher loading and shorter distance/times. The principles remain the same but one person is training for an event that last many hours at a time and one is training for an event that lasts 3-4 minutes.
5) Intermittent or continuous. As per the above answer it is event dependent. Even for the alpinist/mountaineer it will become an interval session when the volume becomes higher. If you have a 1000 foot steep hill but need to do 5 laps like Steve did then it becomes an interval session where he refilled the water at the bottom each lap so he could come down faster. If you are using ME for shorter events like XC then it will be done as interval training. These will vary from 6 to 10 times 30 sec to 2 min work periods, up to 4 x 15 min no poles uphill skating with a 20lb pack for an World Cup Skier.
As with any training there are many variables the influence how you use it. There are no hard and fast rules. No magic formulas. Each individual is going to have a different response. You have to tailor the load, the grade and duration to the person and the event being trained for. What are the muscular demands of your event?