Star, I don’t know what else you want from me. I’ve dealt with every single point you’ve brought up, and yet still, you’re not satisfied. And how do you know my level of intelligence or education? Not that education is even something to base an opinion on, especially when facts rather than opinion are presented. So here, I’m going to lay this whole thing out in facts.
And thus begins my case for explaining why unilateral lifts are better for sprint athletes (See what I did there? Now you can’t go dragging this off into a discussion about powerlifters again.).
To start, strength gained during bilateral training (with squats or DLs) offers more specific improvements in bilateral activities such as the snatch or clean. Strength gained from unilateral activities (like lunges of split cleans) enhances performance more effectively in unilateral activities like running, jumping (off one-leg), or martial arts (Siff, 2004). This alone is a primary reason for a sprinter (whose sport is entirely unilateral) to favor unilateral lifts.
Further along that arc, other studies show that unilateral and horizontal exercises transfer over to sprint performance more easily than bilateral exercises (Young, 2006). And unilateral strength training also results in greater increases in performance in unilateral athletic movements and increases in relative power when compared to bilateral strength training (McCurdy et al, 2005). Furthermore, strength gained on a bilateral training regime does lead to greater increases in bilateral force generation, but increases on a per leg basis are considerably higher after training with unilateral exercises (Hakkinen et al, 1996).
There is also reflex strengthening to take into account with single leg work. Movements such as split squats and bulgarian squats involve the stumble reflex, in which the extension of one thigh potentiates the flexion of the other, and vice versa (Bosch & Klomp, 2001). Sprinting relies heavily on this reflex and strength training and plyo training done in a split position can capitalize on it as well.
And in addition to reflex-specificity in training, central drive issues also arise in bilateral training. It has been shown time and time again that force produced by bilateral contractions is less than the sum of the forces produced by both the left and the right leg individually (Vandervoort et al, 1984). Yet another blow to bilateral training as it applies to unilateral athletes.
Regarding my distaste for traditional max strength work, which I’m going to define here as work above 90% of 1RM, data shows that after a brief period of neural adaptations at the onset of training, further strength increases are accompanied by increases in muscle cross sectional area (Sale, 1988). This means that beyond an initial point (which trained sprinters have long since passed), hypertrophic gains are required to see increases in strength. Bringing it around to sprinters more specifically, not only is sprinting performance strongly correlated with the strength in the hip extensors and flexors, but the strength of the muscles is correlated with their CSA, and this is in trained sprinters. Along this same line, faster sprinters demonstrate greater muscle thickness in the upper region of their thighs (Kumagai et al, 2000) and it has been shown that general hypertrophy training (with loads of 80%) leads to such accumulations of mass (Narici et al, 1996).
Stepping outside of the realm of sprinting for the moment, even Olympic medalist weight lifters of the 1980s employed submaximal sets of 3 on squats most commonly and on accessory work mostly stuck to sets of 5-8. Similarly, only 7% of their training load of competition lifts was above 90% 1RM (Zatsiorsky, 1995). So even athletes whose sports are entirely dependent on lifting heavy weights spend the vast, vast majority of their time and effort outside of the 90%+ range. For sprinters, who already face large quantities of intense training in the form of sprints and plyos, the time spent in the weight room on true MaxS training (90%+ 1RM) should be limited.
Not only does MaxS training cause minimal hypertrophy, but its gains in strength have their own neuromuscular specificity (Siff, 2004). And when volume of MaxS (or any other high intensity strength training means) is too high, burnout is not only a possibility, but an inevitability (Zatsiorsky, 1995). All of these are further reasons why true MaxS work is not needed and may actually be counterproductive to sprinters (especially when the total high intensity volume of their training is taken into consideration). In addition, increased performance is primarily a result of neuromuscular skill, and increased strength is only useful when it is demonstrated during the same type of movement as the sporting movement (Sale & MacDougall, 1981). This means that any neuromuscular gains in MaxS gained via MaxS specific training will only transfer over into similar movements. And on that note…
As I’ve pointed out before, the factors comprising the generation of MaxS are primarily the muscular CSA, the quality of contractile proteins, intramuscular coordination (the synchronization of fiber firing), the strength of the neural impulse (central), and intermuscular coordination (how the muscle interact with one another) (Siff, 2004). Again, MaxS-specific training will develop all of these things, but so will sprint and plyo training. And the differences come in in that intermuscular coordination is task-specific, strength of the central drive is best trained by reflex driven activities (ie. sprinting and plyos), sprints and plyos will result in high quality of contractile proteins, and muscle CSA is best increased (especially in the right areas) by training with roughly 80% 1RM.
That’s about all I’ve got. I’ve laid out my claims, backed them all up with research, and have stopped the petty name calling (which I probably started, but oh well). As for the things which weren’t dealt with, such as the reduced spinal loading, well that’s just a matter of looking at the situation for yourself. I can’t forcefeed you insights, but hopefully I can do so with facts.
References:
Bosch F, Klomp R (2001) Running: Biomechanics and Exercise Physiology Applied in Practice. Reed Business Information
Hakkinen K, Kallinen M, Linnamo V, Pastinen UM, Newton RU, Kraemer WJ (1996) Neuromuscular adaptations during bilateral versus unilateral strength training in middle-aged and elderly men and women. Acta physiologica Scandinavica 158(1): p. 77-88
Kumagai K, Abe T, Brechue WF, Ryushi T, Takano S, Mizuno M (2000) Sprint performance is related to muscle fascicle length in male 100-m sprinters. Journal of applied physiology 88(3): p. 811-816
McCurdy KW, Langford GA, Doscher MW, Wiley LP, Mallard KG (2005) The effects of short-term unilateral and bilateral lower-body resistance training on measures of strength and power. Journal of strength and conditioning research 19(1): p. 9-15
Narici MV, Hoppeler H, Kayser B, Landoni L, Claassen H, Gavardi C, Conti M, Cerretelli P (1996) Human quadriceps cross-sectional area, torque and neural activation during 6 months strength training. Acta physiologica Scandinavica 157(2): p. 175-186
Sale DG (1988) Neural adaptations to resistance training. Medicine & science in sports & exercise Supplement 20: p. 135-145
Sale DG, MacDougall JD (1981) Neuromuscular adaptation in human thenar muscles following strength training and immobilization. Sports Coaching associates of Canada: p. 1-7
Siff MC (2003) Supertraining 4th Ed. Supertraining International, Denver
Vandervoort A, Sale D, Moroz J (1984) Comparison of motor unit activation during unilateral and bilateral leg extension. Journal of applied physiology: respiratory, environmental, and exercise physiology 56: p. 46-51
Young WB (2006) Transfer of strength and training to sports performance. Internation journal of sports physiology and performance 1(2): p. 74-83
Zatsiorsky VM (1995) Science and practice of strength training. Human Kinetics, Champaign, Illinois