Introduction The subject of explosive weight training is one that has been in the center of a maelstrom among strength and conditioning practitioners for quite some time. The National Strength and Conditioning Association (NSCA) recently published a position paper35 advocating the use of so-called explosive weight training movements, which purportedly offer trainees a distinct advantage in speed and power development over those who choose to incorporate more controlled movements. It is also suggested in the position statement that explosive weight training movements prepare the body for the exorbitant, potentially traumatic forces of competition more so than other strength training techniques.
For the purpose of this article, only the explosive lifts will be discussed. These include -- but are not solely restricted to -- the Olympic lifts (i.e., the snatch and clean and jerk), power clean, speed-squats, push jerks and any variations of these movements. Basically, any movement performed in a rapid, jerky manner where momentum plays a key role in the execution and/or completion of the movement would be included.
The intent of this paper is three-fold: (1) to elucidate the fact that ballistic weight training movements carry with them the highest injury potential of any resistance exercises performed in the weight room setting; (2) to dispute the erroneous notion that there exists a definitive physiological or biomechanical mechanism by which ballistic weight training movements result in a distinct and irrefutable advantage over controlled, high tension resistance exercises in producing and/or enhancing speed, power or athletic skill development; and (3) to offer safer, more efficient and more productive training alternatives.
The Risk Factors
It is an accepted premise that all types of resistance modes and/or ideologies will have a certain degree of risk attached to them. This is why instruction and supervision are paramount in resistance training programs, regardless of the lifting movements being performed. There will also be contraindications regarding exercise prescription in isolated cases due to past injuries, structural abnormalities and other physical impediments. As with any physical activity, there exists an assumption of risk with strength training and this is why the participants must be well-schooled regarding lifting/spotting techniques and the myriad of safety guidelines which are of utmost importance in the weight room setting. With judicious care, the majority of the environmental risks associated with the weight room can be effectively controlled.
However, the aforementioned ballistic lifts are immersed in inherent dangers, even when supervision and correct techniques are evident. There exists a preponderance of evidence4,5,8,9,10,14,17, 21,22,23,29,33,34,38 indicating that so-called explosive weight training movements carry a high risk of injury, both acutely and cumulatively, to muscle tissue, fascia, connective tissue and bony structures. Westcott38 states that the acceleration and deceleration forces placed on involved tendons, ligaments, muscle fascia and bone create both initial and terminal stresses on these structures which are likely to produce training injuries.
Several of the lifts being examined here -- primarily the Olympic lifts, power cleans and their analogs -- cause repetitive forced hypertension of the lumbar spine. This forced hyperextension can lead to any number of physical anomalies and injury defects including lumbar sprain, strain, disc injury or a condition known as spondylolysis, which consists of a fracture of the pars interarticularis (an area between the superior and inferior articulating facet on a single vertebra). Dangles et al.3 noted a 44% incidence of spondylolysis in a group of 47 Olympic lifters, while Kotani et al.22 identified the condition in 30.7% of 26 male lifters. It is important to note that these were experienced lifters. Dr. Lyle Micheli, a past president of The American College of Sports Medicine (ASCM), has also indicated that ballistic weight training contributes to spondylolysis.14
While the low back region is a major concern with regard to the injury potential of these lifts, their nature embodies concern for other areas of the body, as well. Dr. Fred Allman, another past president of the ACSM, has commented on numerous occasions on the danger in performing Olympic lifts, as well as the hazards of introducing speed to weight lifting movements. Dr. Allman has also stated that the performance of the Olympic lifts provides little benefit to athletes in their training programs for any sport other than Olympic lifting.9
Kulund23 has mentioned injuries to the wrist, elbow and shoulder while performing Olympic lifts -- injuries which were obviously related to the acceleration and/or deceleration forces imposed on these areas. Hall17 concluded from her study on the clean and jerk that fast lifting speeds generate dramatic increases in compressive force, shear force, torque and myoelectric activity in the lumbar region.
Matt Brzychi, the Strength and Conditioning Coach at Princeton University, offers this perspective: "Using momentum to lift a weight increases the internal forces encountered by a given joint; the faster a weight is lifted, the greater these forces are amplified -- especially at the points of acceleration and deceleration. When these forces exceed the structural limits of a joint, an injury occurs in the muscles, bones or connective tissue. No one knows what the exact tensile strength of ligaments and tendons are at any give moment. The only way to ascertain tensile strength is when the structural limits are surpassed."11
Dr. Ken Leistner, who has long excoriated ballistic lifting in training programs, points out that the inclusion of these movements in strength programs may, in fact, be the genesis of injuries incurred later in practice or games. As Dr. Leistner states, "...the continuous exposure to acceleration/deceleration forces present when doing cleans, snatches and jerks can produce tissue damage which literally is the accident waiting to happen."26 In younger athletes, the risks of damage to the epiphyseal area on the bone is also a cause for concern, as complete ossification may not take place until the late teens or older.
The NSCA position paper takes to task the injury potential of this type of weight training by citing the Zemper et al study,40 which looks at time-loss injuries incurred in the weight room. The NSCA interjects, "Many of the exercises used by those players would be considered speed-strength exercises... the average team can expect one time-loss injury from the weight room every three years." The unanswered questions, however, include: (1) How many of the injuries incurred were a result of ballistic training?: (2) This survey measured acute injuries; what about cumulative trauma which was aggravated on the field and not attributed to the weight room?; and (3) Is any injury in the weight room acceptable? In the injury potential discussion of the position statement, it is disturbing that there is no mention whatsoever of the single most vulnerable area subjected to the compressive and shear forces propagated by the majority of the ballistic lifts -- the lower back region.
Another notion presented in the position statement, which is sure to be heavily scrutinized by the sports medicine community, is that explosive weight training movements are necessary in increasing the tensile strength of viscoelastic tissue as well as increasing bone density and strength. While it has been shown that progressive resistance training, in general, can accomplish these goals, there exists no definitive scientific finding indicating that explosive lifting induces a better adaptation than high tension, velocity-controlled movements. Heavy resistance movements -- relative to the parameters of the repetition scheme, safe range of motion, and controlled movement speed (which will be addressed in the next section) -- will strengthen the aforementioned tissues without the introduction of unnecessary momentum.6,7,11,15,21,25,26,31,32,38 You need not perform ballistic weight training movements for injury prevention purposes any more than you need to pound your head with a hammer in order to prepare for a concussion.
Contrary to the suggestions of the NSCA, injuries do occur in the weight room and have been documented in the literature.5,9,10,29,33,34 Many of these injuries can be directly contributed to ballistic lifting, not merely the failure of the participants to comply to safety guidelines. Also, it is categorically unacceptable to compare weight room injuries to sports-related injuries and to subsequently state that there are fewer injuries in the weight room. Strength training for athletics is not a sport, nor is it an activity where injuries should be commonplace. The comparison is ludicrous.
It should also be noted that certain sports, especially football, place inherent technique stresses on the lumbar spine.16,18,19,26,36 In light of this, performing ballistic lifts, which have proven to be traumatic to the same region, is hardly the prudent thing to do. For example, the Zemper study noted a total of 18 injuries involving either the lower or upper back. The majority of the total injuries were incurred by defensive linemen and offensive linemen/tight ends (19 total). It would be interesting to note the type of lifting which was being performed when these injuries were sustained, but the study fails to examine those important specifics. Dr. Zemper states that the most likely explanation for the higher incidence of injury in these positions is that "...they tend to spend more time in the weight room and generally are lifting more total weight."40 Could the actuality that these positions are also ones most persistently directed by their coaches to perform cleans, snatches, etc., be a factor as well?
The NSCA's underlying tone when discussing injuries is that they are a part of athletics, therefore the fact that certain lifts may carry inherent risks must be accepted. This thinking represents a negligent, haphazard approach in the training of athletes who are not competitive weightlifters.
In concluding this section of the paper, it is important to note that the American Orthopaedic Society for Sports Medicine, an organization which happens to distinguish between strength training and weightlifting in it's position paper, contraindicates the Olympic lifts in training regimens. Also, the ACSM, the world's foremost authority on training protocol since being founded in 1954, recommends safer movements in their strength training position paper and makes no mention of the inclusion of Olympic lifts in training .6
There is no question that the medical community needs to become more actively involved in this controversy. It is my personal belief that, with their continuing input, we will be able to slam the door on this dangerous and unnecessary type of lifting for the general athletic population.
Ballistic Weight Training is Unnecessary
It is the contention of the NSCA that ballistic lifting movements are necessary in enhancing athletic performance in addition to "simulating movement patterns and velocity and acceleration patterns of many sports movements." These claims are not supported with definitive, conclusive research data. While the NSCA cites numerous "suggestions" taken from bits and pieces of the scientific literature which fit into their ideology, the smoking gun is nonexistent. At best, the conflicting data and/or lack of irrefutable findings on these matters render the entire controversy inconclusive.
One promising aspect of the position statement is that the NSCA has finally conceded that, "Slow movement speed does not necessarily mean that an exercise is not explosive. A slow movement may be considered explosive if the athlete applies maximal force as rapidly as possible, although the weight moves slowly due to its great inertia." If one performs a maximum or near maximum set of an exercise within a given repetition range, this "controlled explosion" will be in effect for the majority of the reps performed. This type of training can be done with exercise machines, free weights and the various velocity-controlled modes (i.e., isokinetic devices). It is definitely a safer way to train and, as will be explained in the remainder of this section, is a more efficient manner in which to train.
Any type of progressive strength training will elicit gains in muscle hypertrophy and strength with concurrent enhancement in the contractile properties of muscle tissue.6,8,11,27,39 However, high force/low velocity movements produce longer periods of continuous muscle tension during both the concentric and eccentric phases, thereby placing heavier demands on the target muscles.7,11,12,15,27,31,32,39 There exists an inverse relationship between movement speed and muscle force production, which dictates that maximal tension is developed at slow velocities (though the "intent" to move rapidly is evident) and decreases as the speed of contraction increases.7,8,12,15,27,31,32,38,39 Low force/high velocity movements, therefore, are less productive with respect to maximal force production and concomitant strength development.
While there exists considerable controversy in the scientific literature on the mechanisms of motor unit recruitment, the most widely accepted precept is the "size principle" of activation.7,12,15,27,32,39,40 Henneman39 states that the size of the newly recruited motor unit increases with the tension level at which it is recruited. Basically, smaller motor units are recruited first, with successively larger units firing at increasing tension levels. Slow twitch units (Type 1) tend to be smaller and produce less overall force that the intermediate and fast twitch units (Type II A, Type II AB or Type II B). A major difference in the speed of contraction between the Type I units and the Type II units (including the intermediate Type II fibers) is the fact that they have different degrees of myosin ATPase activity. Myosin ATPase is intimately involved in the muscle contraction process and the fibers that have more of this activity can contract more rapidly. Also related to contractile speed is the fact that slow twitch fibers have a very poorly developed sarcoplasmic reticulum when compared to fast twitch fibers. This may help explain the response of slow twitch fibers to stimulation, as the sarcoplasmic reticulum is important for the quick release of calcium to trigger contraction. Couple this with the fact that the troponin of Type I fibers has a low affinity for calcium when compared to the continuum of Type II fibers, and a clearer picture of the differences in contraction capabilities surfaces. There are also numerous metabolic differences between slow and fast twitch units, due to oxidative properties which dictate energy production and endurance capacities (e.g., mitochondria supply, glycogen stores, etc.).
The element most germane to this discussion, however, is that of neural innervation. Slow units are innervated by motor neurons that tend to be much smaller -- both in the diameter of their axons and in the size of their cell bodies in the spinal cord -- than that of fast motor units. In addition, the net conduction velocity is much slower in the nerves of slow motor units. These differences in innervation elicit a lower threshold for activation in the slow motor units as compared to the fast motor units. The net effect of this neural mechanism is that slow units are recruited first for nearly all activities, regardless of movement speed.7,8,11,15,27,32,39,40 It is only when the intensity of activation is very great, or when the slow twitch units are fatigued that the larger, more powerful fast motor units are brought into play.
Herein lies much of the controversy regarding fiber recruitment: Is there a preferential recruitment of the fast motor units when fast movement speeds are employed? Again, literature exists where "implications" and/or "suggestions" are made in favor of such an occurrence, but the preponderance of currently available data do not support this viewpoint. Lesmes et al.27 state that both muscle fibre types are actively recruited during maximal muscular contractions, regardless of the movement speed. The entire "size principle" of fiber recruitment is predicated on muscle force production, not the actual speed of movement. As can be gathered from this discussion thus far, slow motor units are quite capable of initiating fast speeds of limb movement if the force requirements are low. Therefore, if the training goal is the recruitment and development of the fast twitch muscle fibers, fast weight training speeds at low intensity (i.e., high velocity/low resistance movements) represent the least efficient approach. As stated by Pipes, "Speed of limb movement has little to do with intensity. If anything, there is an inverse relationship ... you can have speed or you can have intensity; you cannot have both."31 Studies by Palmieri30 and Wenzel et al.37 measured training speed and power development with no significant differences being found at slow, fast or a combination of slow and fast speeds. The relevance of these studies is in the conclusion of each that fast training speeds are not needed for power improvements. If controlled speed is at least as effective (if not more so) and safer than faster speed, wouldn't the controlled movement speed be the more judicious option? More importantly, if the safety and welfare of those athletes entrusted to you truly supersede any personal preference or commercial bias in training techniques, then the choice should be quite obvious.
"Movement specificity" is a term that has long been misinterpreted by the NSCA. To say that, "the snatch and clean are very similar to other athletic movements such as jumping," is to contradict many of the basic principles of motor learning. While it is beyond the scope of this paper to go into an in-depth discussion on skill-specifici