Strength coaches write training programs for athletes primarily with the goal of developing transferable strength for their sport. However, they often have the secondary goal of increasing muscle size.
Some research indicates that training to muscular failure may improve gains in muscle size, and this has caused some strength coaches to incorporate taking sets to failure into their training programs.
Even so, there are actually a number of very good reasons why training to failure is not the best approach when training athletes.
#1. No incremental benefit when using heavy loads
Assuming that an athlete primarily needs to improve maximum strength (and not high-velocity strength), then heavy loads are better than moderate or light loads for this goal.
This is because heavy loads enable a range of other adaptations that enhance gains in maximum strength, including increases in tendon stiffness, lateral force transmission, voluntary activation (neural drive), and load-specific coordination.
Training to failure enhances gains in muscle growth by increasing the amount of motor unit recruitment. However, when using heavy loads, motor unit recruitment is almost certainly full irrespective of the amount of fatigue that is present.
Therefore, it is very unlikely that training to failure will have any meaningful effect on the resulting hypertrophy when using loads >85% of maximum strength in a training program, and these are the percentages of one repetition maximum (1RM) than most strength coaches will (hopefully) be using when developing maximum strength.
#2. Smaller gains in high-velocity strength
Assuming that an athlete primarily needs to improve high-velocity strength, then lifting light loads with fast bar speeds, while avoiding fatigue is valuable for achieving this goal.
Research has shown that by stopping sets before fatigue causes a reduction in bar speed, gains in high-velocity strength and transfer to sports performance in fast movements like sprinting and jumping can be enhanced (although muscle growth is reduced).
Strength training naturally causes a shift from very fast (type IIX) to moderately fast (type IIA) muscle fibers, and this has a negative impact on high-velocity strength. This is why conventional strength training always produces greater improvements at the force-end of the force-velocity spectrum than at the velocity-end.
However, by stopping sets before fatigue causes a reduction in bar speed, the proportion of type IIX fibers that are converted to type IIA fibers can be reduced, and this may contribute to the proportionally greater gains in high-velocity strength.
#3. More muscle damage
We tend to think of muscle damage as being caused by heavy eccentric (lowering) muscle contractions because of disruptions to the muscle fibers caused by the high levels of mechanical loading.
However, it seems very likely that muscle damage can also be caused by a sustained excitation-induced influx of calcium ions under conditions of low energy status and hypoxia, which is what happens when training under fatiguing conditions.
When levels of calcium ions are elevated for extended time, proteases known as calpains and phospholipases are activated. These break down the ultrastructure of the muscle cell and the sarcolemma, and can cause muscle fiber damage.
Thus, it is likely that training to failure causes more muscle damage than avoiding failure, even when using very light loads. This may reduce motivation to train, decrease the ability of an athlete to train regularly, and interfere with competition performance. Whether regularly experiencing higher levels of muscle damage also any adverse long-term effects is unknown.
#4. Slower recovery, and lower training frequency
Athletes often need to train regularly, and strength training workouts are sometimes squeezed into gaps in a congested schedule of sports practices, conditioning, and competitions.
Therefore, it is helpful if a training session does not require a long period of time to recover from, as this can reduce the number of training sessions that can be done each week, disrupt other training, and interfere with match performance.
Training to failure increases the length of time that is needed before another strength returns to baseline levels, likely for several reasons, including a greater depletion of energy stores within the muscle, higher levels of peripheral fatigue, and greater muscle damage. And importantly, the amount of recovery time required when training to failure is greater when using lighter loads, compared to when using heavy loads.
What is the takeaway?
Training to failure likely has no incremental benefit for hypertrophy when training with heavy loads to achieve gains in maximum strength, because it works through increasing motor unit recruitment, and motor unit recruitment is already full with heavy loads. Also, it has *adverse* effects when trying to improve high-velocity strength, because it accelerates the conversion of fast to moderately-fast muscle fibers, which reduces contraction velocity.
Training to failure likely produces more muscle damage compared to not training to failure, perhaps through a mechanism involving the prolonged release of calcium ions triggering the degradation of the inside of the muscle cell. Moreover, it reduces training frequency by increasing the time taken to recover from a workout, compared to avoiding failure, and this effect is larger when lifting light loads than when using heavy loads.