I would assume everybody has some basic understanding of this, as most people tend to instinctively make fun of people pursuing too many incompatible goals at a time: the proverbial guy that wants to grow his muscles, shed body fat, grow stronger as to impress everybody in his Globomax gym, run a marathon under three hours and compete in the local basketball league and take fencing (or boxing, or MMA) normally doesn't get too far in any of those areas, although I would venture to say that just being mediocre in all of them at once takes a considerable amount of gumption already (when excellence reaches the level our hypercompetitive and resource-rich societies allow it to reach, even being mediocre requires a lot of dedication).
So in this post I'm going to deal with what kind of distinct abilities can be improved through training, and what kind of directions should be followed to develop each of them. Some of the abilities can (even should) be developed in unison, some are antagonistic, and typically improving one would result in loosing (or at the very least not progressing) the other. Understanding why that is so should give us clearer guidelines about what it is realistic to try to achieve or, as the title of the post suggest, what to train for:
- Strength: I'm putting this first as it is the foundational quality for many of the more specific attributes I'll describe later on. It reflects the ability of the muscles to overcome a certain resistance, so the more resistance that can be overcome, the stronger the muscle is. Although muscular action is local (a man could theoretically have very strong biceps brachialis, but very weak hamstrings and quadriceps, as many regular gymgoers obsessed with curls and averse to squats seem to have) it tends to develop holistically, specially if the right exercises are chosen (the aforementioned squats have a global organic effect that somehow manages to make people who do them consistently and forcefully strong overall). It is probably the easiest quality to develop, it admits an almost infinite level of progress (albeit, thanks to the law of diminishing returns, the same amount of progress becomes more and more costly as one approaches his genetic potential) and it doesn't start to diminish after reasonably late in life (I'm 45 myself, and still growing fairly stronger every month, and know of goddamn stronger people well in their fifties). There is no black magic or secret principles for developing it: as many series of 3-5 reps of a few basic, compound, multi articular exercises (basically squat, deadlift, bench press, press and their variations, plus chin ups and dips is all you need to grow obscenely strong), increase weight on the bar in each one of them, and after an initial phase of quick gains, periodize (alternate phases of higher volume and lower intensity with lower volume and higher intensity, reaching new peaks after each cycle).
- Speed: reflects the ability to move the body through space as fast as possible. It is even more systemic than strength, as I've never seen anybody have fast feet but slow hands (or any such imbalance). It is considered a highly innate quality, based on genetic factors like insertion points of the tendons and proportion of muscle fibers of each type (fast twitch vs slow twitch), so the most optimistic coaches tend to say it is difficult to improve it beyond a 20% of its baseline value. A school of thought maintains that for most applications there is little value in trying to train a quality so little amenable to improve, and thus recommends focusing on strength increases (so, even if force is applied as slowly as before, more force can be transmitted, and more acceleration obtained, applied to running mechanics there is a lot of merit to that approach, but applied to shot putting not so much). I tend to agree, with a small caveat: I've noticed (mostly in myself) that moving a limb really fast requires not only a contraction of the muscle that accelerates the limb, but the quick relaxation of the agonist muscle that would decelerate it. So although the speed at which a muscle contracts can not be much improved, the speed at which it looses tone can, and that alone contributes to a more significant increase in speed. The by now traditional way of increasing speed is through "shock training" (vertical jumps, depth drops, bounded jumps, medicine ball throws, very short sprints) and barbell explosive movements. As I wrote in a previous post (The Olympic lifts and their power versions), I think the reason full Olympic lifts are better than their power versions is because they teach the organism to relax fast. All those movements are best trained with many sets of very few reps (1-2, maybe a max of 3), rested enough as to allow for maximum speed in each set, and with weights that allow for a safe execution
- Endurance: consists in the capability of the organism to keep moving during longer periods of time. It is even more systemic than speed, as it heavily relies in systems (cardiorespiratory and endocrine) that are shared by all the muscles. When the movement requires displacing the whole organism without the aid of a supporting medium (like in swimming, when water keeping us afloat greatly reduces the disadvantage of a heavier frame, or in cycling, where the bicycle supports the load) it substantially favours lighter people, to the point where carrying a substantial body mass (regardless of it being mostly fat or mostly muscle) is an insurmountable handicap in most endurance events. In its initial stages of development it can be trained very efficiently with very short and intense bursts of activity (sprints) interspersed with rest periods at a more leisurely pace, although at higher levels it requires the drudgery of going out to train for long duration sessions of "pavement pounding" of some sort. As far as I know, only Alex Viada thinks this kind of capability can be consistently developed in parallel with being stronger overall, and for the rest of the universe they are utterly antithetical, as the enmity between joggers and meatheads attest
- Coordination: under this final tag I'm grouping all the qualities that demand a fine motor control and an exact sequence of motor firing in order to obtain a very precise path for the involved body parts (both in terms of trajectory and velocity). It is shown in things like throwing a basketball towards the hoop, pitching in baseball, swinging in golf (not a sport, but an activity with some very subdued physical demands that tend to be overemphasized by their practitioners), putting the shot or performing a snatch or a clean & jerk. Specificity for this feature is the key, thus the only way of improving it is to accumulate endless hours of quality practice (that is, practice initially under the watchful eye of an expert that can correct and guide the development of a perfect movement pattern, and even when mastery has been achieved, under conditions that allow for as much feedback as possible)