When we train long duration efforts, we REDUCE athletic performance (relative to that individual’s potential). Low speed efforts train a person to become less powerful, lower balance, and, as the reader might expect, lower speed. This is why jogging and walking can be suspect for individuals who want to dramatically improve health and fitness. Low resistance with slow reps can be not just a waste of time but an ally in reducing your fitness.
Zoom in on the table to see how even resistance training aimed at size gain/muscular failure is inferior at athletic performance results.
There are three types of skeletal muscle fibers: I, IIA, and IIX. They’re also known as Slow Oxidative, Fast Oxidative, and Fast Glycolytic, respectively. Each serves a different portion of the energy spectrum. You can also see why, when referencing this terminology, people who want to improve health prospects regarding prediabetes ought to spend some time working on type IIX (as the name implies, glucose is disposed). To be clear, once skilled enough to be safe, people should be training speed and training maximal weights WITHOUT going to failure. Training for advancement in one area reduces the relative outcome in the other two. This is a biological law, not something which can be subverted by force of will or hoping it isn’t true.
And it’s imperative that the fitness professionals and laypeople keep this in mind. Most popular programming and pop fitness recommendations aren’t just untrue. They’re counterproductive for most of the populace most of the time. Professional athletes and fanatics who train 15-40+ hours per week are often succeeding IN SPITE of inefficient programs. The average person can’t afford the time to use nonsense recommendations from gifted genetic freaks or uneducated fanatics.
For the absolute beginner, yes, just begin with movement, any movement. After that stage, endeavor for some muscle gain in order to combat lean tissue loss. But for athletic improvements (ie - agility, balance, speed, acceleration, power), low speed exercise, including to muscular failure, doesn’t yield as good of results as high speed ands strength.
Everyone runs out of time in a given week, which is where periodization enters. That is, to glean benefits for all energy systems, one can emphasize one modality of training for a period of weeks or months before moving to another. Just remember: each one causes a relative reduction in the others.