Reactivity: What It Is and How to Get It - II: Having already given a brief rundown of what reactivity is (using energy gained during the eccentric to potentiate the concentric) and how to recognize and test for it, this installment seeks to explain the muscles' and tendons' contribution to reactivity without delving too far into the neural side of things, that's for later. To break down exactly what happens from a perspective of only the muscles and tendons when reactivity is displayed, we'll look at what is perhaps the single most reactive movement in existence: top speed sprinting. At top speed, a talented sprinter's foot may only be on the ground for .10 seconds or less, but during that time he will experience well over 4 times his bodyweight worth of force on that one foot. Naturally, our muscles are not able to voluntarily create that much force, that quickly, but if developed correctly, our tendons can. As the foot touches down, the muscles of the leg (the question of which muscles is not directly important here, but for explanation's sake it's mostly the calves, glutes, and hamstrings) experience massive forces applied suddenly. If they're strong enough, the eccentric phase is minimal and the muscles lock up isometrically in well under 1/20th of a second. At this point, as the muscles remain static, the force from the step reaches the tendons and causes them to stretch. Deforming only the smallest of lengths, the tendons take in energy like a spring being loaded, and only an imperceptibly small moment later they release that energy back into the ground and the concentric portion of the movement begins. So, as one can see from the above, staying solely on the physical side of things, what one needs to properly display reactivity is: muscles that are eccentrically and isometrically strong, and stiff tendons (ie. tendons that are resistant to deformation under load). Some types of training build both of these attributes, and other types only focus on one or the other. No matter which though, we'll get a good look at them all.   The Muscles: In order to absorb the massive forces encountered in sport one needs exceptionally strong muscles, but the strength most needed by sprinters and jumpers is not concentric in nature, but eccentric and isometric (Dursenev & Raevsky, 1979). Contrary to popular belief, muscular strength is somewhat specific, and just because one person exhibits higher levels of concentric strength than another (such as in a squat, deadlift, or a standing vertical leap), does not mean they will have higher eccentric or isometric strength (as demonstrated by sprint speeds, reactive squats, or approach jumps). Specific training regimes produce specific increases in strength, meaning that eccentric-dominant training will produce the highest gains in eccentric strength, concentric-dominant training will produce the highest gains in concentric strength, and isometric-dominant training will produce the highest gains in isometric strength (Siff, 2003). So, as is now obvious, not all strength training is equal. For those who care about their sprinting speed and leaping ability, the focus needs to be on methods that increase eccentric and isometric muscular strength. Before we get too far off the deep end however, I should not that even though strength gains are quite specific, they do have a general carryover. This means that while regular barbell squats may not be the best choice for building eccentric and isometric strength in the quads and glutes, a large strength increase made while using them will result in eccentric and isometric improvements, but not nearly as large of ones as made in concentric strength. The same goes for other modes of training as well. Moving on, since strength gains are largely specific, someone looking to increase the reactive potential of their muscles would want to focus on strengthening them eccentrically and isometrically. This can be done using a couple of different methods which I'll cover here. +Overload Eccentrics -Overload eccentrics involve slowly lowering a weight that is beyond 100% of one's concentric maximum. So, if one can back squat 200 kg, they would be using more than 200 kg for this method. Usually the weight is kept between 110-120% of one's traditional max. This type of weight can be lifted (or lowered in this case) because one's capacity for eccentric strength is usually 20-60% higher than their capacity for concentric strength (Hollander et al, 2007). -Since the intensity of this method is so high, the volume is usually kept very low. Even so, this method induces high levels or muscular soreness and carries a high chance of injury and/or burnout if applied incorrectly or excessively. For these reasons, this method is not commonly used with novices, or very often with anyone, even though it does result in large specific strength increases. +Yielding Isometrics: -When one thinks of isometrics they usually think of someone pulling or pushing against an immovable object. These are what is known as overcoming isometrics, and they're not what we're looking for. What we're looking at is yielding isometrics. In using this method, one takes a weight and holds it at the bottom of a movement for time. For instance, if one were to use this method for the bench press, they would lower the bar to about an inch off the chest and hold it there until failure. It's the same concept with other lifts. As with eccentrics, one's capacity for isometric contractions is usually 10% higher than their capacity for concentric contractions. -When training for maximal isometric strength, yielding isometric holds are best kept under 20-25 seconds in duration, and longer than 5 seconds in duration. Though loads used in this method are high, they're not too high and thus this method isn't too draining. Residual soreness is relatively low as well. This method can be used as often, if not more often, than traditional weight training.   The Tendons: Whereas the muscles need to lock up and hold tight in order for the body to execute reactively, the tendons don't have the ability to actively contract, but they still need to be strong. Since it's the tendons that actually stretch and then return the force during reactive movement, it's imperative that they be given just as much consideration as the muscles in one's training. Using an analogy, the tendons can be thought of as springs, as they both perform exactly the same function. And in this case, the stiffer the springs, the better. The more resistant to deformation one's tendons are, the more energy they can store before they rupture (I know, just thinking about it is horrible), and the quicker they can store and re-exert it. Top athletes such as sprinter Asafa Powell or high jumper Stefan Holm have tendons that are not only significantly stronger than regular men and women, but much stronger than those of even their professional peers. But how exactly does one build stiff tendons? The answer is fairly simple. The higher the load a tendon is exposed to, the more collagen it will synthesize and the stiffer it will become. As such, even things like weight training can increase tendon mass and stiffness, but this is not where the highest forces are found. The highest forces in sports are found in high speed, reversible muscle actions, such as during sprinting or jumping. Naturally, if we want to strengthen the tendons, these are the movements we would seek to use in training. +Sprints: -Sprint training exposes the body to very high levels of force (especially through the hamstrings and calves) and is mainly reliant on the stretching of the tendons and is therefore a good choice for those seeking increased tendon (and ligament) strength. Research has shown that sprint training is effective in increasing connective tissue mass (Tipton et al, 1975) and it is therefore a good choice. -When sprinting, it is best to keep the intensity above 90% and to make sure adequate rests are taken in between runs to avoid performance decay or injury. Depending on one's ability level, it can take anywhere from 48-72 hours to recover from a good sprint session. +Approach Jumps: -If an athlete wants to get good at something then they'd better practice it, and jumping is no exception. If an athlete wants to jump higher from an approach, then they're going to need to do full approach jumps regularly. Again, whether off of one foot or two, the forces encountered in approach jumps are very large and are born largely by the tendons, thus this method is a good one to use. -Approach jumps are very hard on the body and require a lot of energy. For this reason it's best if they're done in sets of 2-3 jumps with ample rest time in between sets. Similarly, the method is very draining both physically and mentally and therefore volume should be watched. +Plyometrics: -We're talking about true plyometrics here, namely depth drops and depth jumps. Both of these methods provide the body with a large overload and if intensity and volume are not correctly administered they can lead to injury. -Plyometrics are very hard on the body, and are typically not for novice athletes. Until one can squat at least 1.5x their bodyweight I would not recommend this method. And even then, volume should be kept minimal and at the first sign of performance decay the sessions should be ended. There should be 48 or preferably 72 hours between each bout of plyometrics. Again, full rest in between sets is wise. +Lactic Acid Accumulation Work: -Strangely enough, even after all the methods listed above, it's anaerobic endurance training that appears to have the greatest effect on tendon and ligament strength (Siff, 2003). This may be due to the link between lactic acid production and the increase of a certain collagen synthesizing enzyme (Booth & Gould, 1975). Regardless of what it's due to though, any anaerobic endurance training is great for increasing tendon stiffness. -Regarding specifics, anaerobic endurance training generally consists of any kind of intense work between 40-60 seconds in duration. This can be sprinting, continuous weight lifting, or even cyclical jumps. No matter what's used, as long as the intensity is high enough and the set duration is correct, the right training effect will be found. Outside of specific training for either the muscles or the tendons, there are some methods that train both simultaneously. Such methods would include reactive lifts (typically using 40-60% 1RM) and full Olympic lifts (using 75-90% 1RM). Neither is best at training purely the muscles or the tendons, but they're a nice “in-between' movement” that can be used in maintenance phases. Summing it up, those are the methods that will be most useful for developing the physical attributes necessary to excel in reactive-dominant sports. By employing them correctly and in a well balanced training plan, one can build a physical base upon which they can learn to best express their reactive abilities. In the next installment we'll be covering the neural factors involved in reactivity and what methods can be used to train them. -Revolution   References: Booth F, Gould E (1975) Effects of training and disuse on connective tissue. Exercise and Sports Sciences Review 3:84-112 Dursenev L, Raevsky L (1978) Strength training of jumpers Teoriya I praktika Fizescheskoi Kultury 4: 56-57 Hollander DB, Kraemer RR, Kilpatrick MW, Ramadan ZG, Reeves GV, Francois M, Hebert EP, Tryniecki JL (2007) Maximal eccentric and concentric strength discrepancies between young men and women for dynamic resistance exercise. Journal of Strength and Conditioning Research 21(1): 34-40 Siff MC (2003) Supertraining Supertraining Institute Tipton C, Matthes R, Sandage D (1975) The influence of physical activity on ligaments and tendons. Medicine and Science in Sports 7: 165-175