The best knee flexor training for strength...

Heavy weights vs lighter weights to muscle failure

Squats are the best exercise for leg development due to their amazing capacity to simultaneously activate most of the major muscle groups of the lower body, generating tremendous muscle growth and huge strength gains. While all the muscle building capabilities of squats are fantastic, there has been some uncertainty as to what training protocol produces maximum strength gains when performing squats. One of the more complex yet seemingly simple questions asked when it comes to assessing the capacity of a particular training approach to build strength is how many repetitions should be performed at what intensity level.

The standard training intensity for mass and strength

The typical training approach for maximum strength in squats uses about 80 to 90 percent of the one-repetition maximum (1RM) weight at a repetition range of two to five repetitions, while 75 to 85 percent of the 1RM weight at a repetition range of four to 12 repetitions is preferred for stimulating muscle hypertrophy. Heavier weights increase strength primarily by inducing greater neuromuscular activation of fast-contracting muscle fibers, which contract faster than slow-contracting fibers and produce more force.

The increased activation of fast-contracting muscle fibers through high-intensity training ultimately leads to greater strength gains. On the other hand, higher volume training more specifically increases muscle growth - in large part by increasing time under tension, which increases metabolic stress, thereby promoting muscle hypertrophy.

Several studies draw attention to the aforementioned differences in training outcomes and emphasize that training for hypertrophy is distinctly different from training designed to preferentially increase strength (1). Good evidence for this principle is that most powerlifters - whose primary goal is to get stronger - typically perform high-intensity training with 85 to 95 percent of their 1RM weight in a repetition range of three to five repetitions, while most bodybuilders use lighter weights in the range of 75 to 85 percent of their 1RM weight and a repetition range of 8 to 12 repetitions.

Stronger muscle contractions equals more strength

A key element necessary to increase strength comes from an increased capacity to activate muscle contractions quickly. It is well documented that moving heavier weights increases the ability to activate muscle contractions and recruit muscle fibers, demonstrating a central mechanism activated by heavier weights that more effectively promote strength gains (2, 3). In contrast, other studies have also shown that increased levels of muscle activity can be induced by using lighter weights with more repetitions (4, 5).

The increase in muscle activity elicited during the use of lower weights with more repetitions has been attributed to the sequential activation of additional muscle fibers that occur to maintain muscle contractions throughout the exercise while accumulating fatigue. As a result, the greater amount of muscle activity resulting from using lighter weights with more repetitions could potentially lead to strength gains comparable to the strength gains observed when using heavier weights. However, the extent of the relative increase in muscle activity when performing more repetitions with lighter weights compared to using heavier weights is still unclear. For this reason, the ability of this training approach to increase strength is still unclear.

Since the muscle fatigue that results from training with higher repetitions induces the activation of additional muscle tissue in a compensatory manner, training techniques that pre-fatigue the muscles more extensively - such as descending sets (drop sets) using heavier weights - could be used to induce greater muscle fatigue, to induce greater muscle fatigue, followed immediately by training with lighter weights to muscle failure - may actually induce an even greater amount of muscle activation and ultimately generate more muscle activity that further increases strength gains.

High-intensity training is superior

Scientists wanted to investigate whether training with higher repetitions and lighter weights could induce similar, or even greater, muscle activity than heavier resistance training. To this end, a study by Looney and colleagues (6) looked at muscle activity in two major muscle groups of the thigh - the vastus lateralis and the vastus medialis - while 10 young men with extensive training experience performed squats with the maximum possible number of repetitions at an increasing load level of 50, 70 or 90 percent of their respective 1RM weight.

The results showed that muscle activity in both muscle groups was significantly higher with a load of 90 percent of the 1RM weight than with squats at 50 or 70 percent of the 1RM weight, with all weights being trained to the point of muscle failure. Training with 70 percent of the 1RM weight resulted in significantly higher recruitment than training with 50 percent of the 1RM weight.

To further investigate whether training with higher repetitions and lighter weights in combination with descending sets can induce muscle activity comparable to muscle activity during heavier resistance training, Looney and colleagues looked at the muscle activity of the same thigh muscles while the subjects performed the maximum number of repetitions of squats with a light weight (50 percent of 1RM weight) immediately after performing squats with 70 and 90 percent of 1RM weight to muscle failure. This was done without resting between sets to maximize muscle fatigue and hopefully induce higher muscle activity. The data showed that using descending sets to pre-fatigue the muscles did not increase muscle activity more than performing a single set with the same 50 percent of the 1RM weight.

All in all, these results confirm the prevailing view that higher muscle activity occurs when heavier weights are used and that the additional use of pre-fatigue techniques such as descending sets does not lead to higher muscle activity during subsequent lower intensity training.

The conclusion from all this research is that heavy resistance training on its own is still one of the most effective ways to elicit maximum muscle activity and increase strength. Although there are other training methods that successfully incorporate the use of lighter weights into training and produce significant strength gains, the use of pre-fatigue techniques at high intensity levels does not produce the desired effect of increased muscular contractility, meaning that this approach is unlikely to be successful in building any significant amount of muscle strength.

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References:

1. Masuda K, Choi JY, et al. Maintenance of myoglobin concentration in human skeletal muscle after heavy resistance training. Eur J App Physiol Occup Physiol 1999; 79, 347-352
2. Duchateau J and Hainaut K. Training effect of submaximal electrostimulation in a human muscle. Med Sci Sports Exerc 1988; 20, 99-104
3. Pucci AR, Griffin L and Cafarelli E. maximal motor unit firing rates during isometric resistance training in men. Exp Physiol 2006; 91, 171-178
4. Hassani A, Patikas D, et al. Agonist and antagonist muscle activation during maximal and submaximal isokinetic fatigue tests of the knee extensors. J Electromyogr Kinesiol 2006; 16, 661-668
5. Pincivero DM, Aldworth C, et al. Quadriceps-hamstring EMG activity during functional, closed kinetic chain exercise to fatigue. Eur J Appl Physiol 2000; 81, 504-509
6. Looney DP, Kraemer WJ, et al. Electromyographical and Perceptual Responses to Different Resistance Intensities in a Squat Protocol: Does Performing Sets to Failure With Light Loads Recruit More Motor Units? J Strength Cond Res 2015 [Epub, ahead of print]