Research results with important implications for your clients’ strength training regimens.
When personal fitness trainers (PFTs) design resistance training programs, they regularly discuss with clients the issue of training to failure—or momentary muscular fatigue. Many trainers adhere to a very strict policy, stating that if muscular “failure” during a set is not achieved, the set will be counted as an additional warm-up set. However, as relevant as this training concept is to resistance exercise, there is surprisingly little research to confirm or deny the premise. Willardson (2007) recently completed a research review and analysis to better understand the known pros and cons of training to fatigue in multiple-set workout plans.
Muscular failure in resistance exercise is the point during exercise performance when the neuromuscular system can no longer produce adequate force to overcome a specific workload. The client must stop the exercise set and recover for a brief (1- to 3-minute) period to allow more immediate energy (i.e., ATP) to be resynthesized. During this recovery time, various metabolic byproducts (e.g., hydrogen ions, lactate, inorganic phosphates, creatine, potassium) inside and outside of muscle fiber tissues are removed or restored. It is important to note that the challenged muscle fibers aren’t entirely fatigued at this point; they just can’t produce enough force to overcome the specific load. If the PFT were to lighten the resistance sufficiently, the muscles would be able to overcome the lighter load.
The theoretical basis for training to failure is motor unit recruitment. The motor unit consists of the nerve and the muscle fibers innervated by that nerve. It is well established in neuromuscular physiology that the recruitment pattern of motor units depends chiefly on the force needs placed on the muscle. Classically, with low threshold challenges, the type I (also known as oxidative) muscle fibers are primarily the ones recruited (see “Characteristics of Muscle Fiber Types” on page 24). As the force becomes greater, the type IIa fibers (also referred to as glycolytic) are recruited. The greatest force-producing fibers in the human body are type IIb or type IIx fibers (the “x” denoting that there are several variations of this fiber type). Therefore, if muscular strength is the main objective, it is felt that the degree of motor unit activation will be directly related to the magnitude of the strength training response.
It is remarkable that the concept of training to failure, which is so rooted in the foundation of resistance training, is based on so little research. In fact, Willardson (2007) notes in his review that some research is quite misleading on this topic, with a few investigators stating that subjects trained to a certain percentage of repetition maximum (RM) and yet not reporting whether failure was attained (intentionally or randomly).
A classic study investigating the issue of training to fatigue was completed by Rooney, Herbert and Balnave (1994). In this investigation, strength increases produced by a training protocol in which subjects rested between contractions were compared with increases produced when subjects did not rest between repetitions (as exercises are commonly performed). Forty-two male subjects were randomly assigned to either a no-rest group, a rest group or a control group (which did no training). Subjects in the two training groups trained their elbow flexor muscles by lifting a 6RM weight 6–10 times 3 days per week for 6 weeks. Subjects in the no-rest group performed repeated lifts without resting, whereas subjects in the rest group rested for 30 seconds between each repetition. Intensity and volume of training were matched. Subjects who trained without rests experienced significantly greater mean increases in dynamic strength (+56.3%) than subjects who trained with rests (+41.2%). Thus, the best short-term strength increases were achieved when subjects lifted weights in the manner that is usual in resistance training workouts.
In a study at odds with the one summarized above, Drinkwater and colleagues (2005) completed an investigation with 26 elite junior male basketball players and soccer players, all of whom had been doing resistance exercise for the previous 6 months. The subjects completed three sessions of bench press training per week for 6 weeks, using equal-volume programs (24 repetitions at 80%–105% 6RM). Subjects were assigned to one of two experimental groups: one was designed to elicit repetition failure with 4 sets of 6 repetitions (RF group); in the other, subjects completed 8 sets of 3 repetitions not to failure (NF group). The RF group demonstrated substantial increases in strength (+9.5%) and power (+10.6%) compared with the NF group in strength (+5.0%) and power (+6.8%).
The mixed findings from these two studies indicate fatigue-related physiological and metabolic processes—other than just training to failure—contribute to the strength training response. More research is needed in this area.
Based on his review of the research, Willardson (2007) encourages not always training to failure, as this may contribute to overtraining and overuse injuries. He also cites three studies that show there may be a decrease in growth-promoting hormones if training to failure is done continually. Willardson suggests that exercisers go to failure in sets every other workout, or even every other week. He also recommends that training to failure should be varied, just as all acute variables of resistance training (e.g., numbers of reps, number of sets, rest between sets, order of exercises, choice of exercises, etc.) are varied in periodization programs. More important, Willardson further suggests that the athlete or client should stop the set when the exercise performance technique is being compromised (e.g., with poor posture, body shifting, accessory movements, etc.) in order to lift the weight.
In addition, for older populations, special populations, those with arthritis and/or osteoporosis and many recreational exercisers, training may be much more valuable when its purpose is to attain function and stabilization goals—which do not require training to failure. Competitive athletes and those clients who are trying to maximize strength and hypertrophy goals may have greater needs to train more frequently to failure in order to reach their performance goals.
Studies clearly show that subjects can positively gain strength and power without always incurring the strict discomfort and acute physical effort associated with failure contractions. As fitness professionals we work with clients on a daily basis, so it is important to add variety and stimulus change to their workouts. Willardson’s research review suggests that, whether for safety or variety, “training to failure” and “not training to failure” are acute variables of resistance training that should be regularly manipulated in program designs.