What is HIT Training – HIT alone is already the abbreviation for High-Intensity Training, which means high-intensity training. The abbreviation “HIT” is often combined with training, to HIT Training. It then means High-Intensity Training Training… 😀 Since the phrase HIT Training is often used, I will write it simply like that in the following text… 😉 This article deals with HIT in strength training. If you want to learn more about HIIT in endurance sports, please check out my article on High-Intensity Interval Training. 🙂

HIT Training 😀 is a training system some athletes use in strength training and bodybuilding to make their muscles bigger and stronger. A characteristic of HIT Training is that it is short but intense. This means that only a few sets with high weights are performed per muscle group, which leads to muscle failure and beyond. HIT differs from “regular” high-intensity strength training in that HIT trains with high loads to the momentary muscle failure and far beyond.

In “regular” high-intensity strength training, loads over 80% of the 1 RM (one repetition maximum; one repetition maximum) are also used.¹ One probably speaks of high-intensity strength training already when one uses loads over 60% of the 1 RM.² Thereby, momentary concentric muscle failure can also be reached^1,2 (Example: You perform 10 repetitions of bench press, but at the last repetition, you can not bring the weight without help from the chest to the starting position. You need help because the muscles were so exhausted that the positive or concentric phase of the movement – barbell from chest height to the starting position – can not be done alone.). But classically, one does not continue after reaching the concentric muscle failure but takes a break and waits for the next set. With training methods like HIT, however, tricks are used to continue training after reaching the concentric muscle failure. What these tricks can be, you will learn in this article.

HIT Training was developed in the 70s by Arthur Jones. He wanted to create a training system that maximally challenges and promotes the muscles in the shortest possible time. Mike Mentzer further developed HIT Training in the 80s and described it in his book “Heavy Duty”. This high-intensity training can have advantages but also disadvantages. In this article, you will learn everything you need to know about HIT Training: Why it could work, who it is suitable for, what advantages and disadvantages it has, how to do it right, and how to create a HIT training plan.

What is HIT training, and why could it work?

First of all, it should be mentioned that the considerations for the original HIT Training probably originated from the training practice. There seem to be no research papers that examine the original “Heavy Duty” training itself or compare it with other training methods. Studies on training methods like HIT are rare in training science research. However, the research has dealt with, for example, what effects a “regular” high-intensity strength training on momentary concentric muscle failure can have. Therefore, at the end of the article, I will go into this to what extent muscle failure in strength training can be beneficial. Everything written here about traditional HIT Training is based only on the assumptions of HIT proponents and not on scientific consensus.

What is HIT training – Characteristics and presumed effects

HIT Training is based, like other training methods, on a progressive load increase. This means that you have to stimulate your muscles more and more from time to time so that they adapt and grow. If you always use the same weight with the same number of repetitions, your muscle growth probably stagnates because your body has gotten used to the load. To avoid this, you would have to change something in the training. You can adjust some variables in the training (weight, rest length, etc.). HIT Training focuses mainly on increasing weight. The goal is to use the maximum weight with each set you can move for a certain number of repetitions. You should aim for 5 – 8 (10) repetitions per set, depending on the exercise, corresponding to about (75%) 80 to 90% of your 1 RM. 1 RM is the weight with which you can only do one repetition. By training with high weight, many, if not all, muscle fibers are activated. In addition, the release of anabolic hormones, such as testosterone and growth hormone, which are important for muscle regeneration and hypertrophy, is stimulated.

Who is HIT Training suitable for?

HIT Training is not suitable for everyone. It requires high motivation, discipline, and pain tolerance to bring the sets to the momentary muscle failure and beyond. In addition, you already should have strength training experience before starting with HIT Training. Beginners should get used to the basic exercises: squat, deadlift, and bench press. In addition, a solid foundation should be built first so that besides the muscles, the tendons and the passive musculoskeletal system can handle high loads. It is also important that a good movement execution can be maintained even under exhausting conditions.

HIT Training can be suitable for athletes and fitness enthusiasts who meet the above requirements but have little time for training but still want to achieve maximum results. HIT Training probably lasts only 30 to 45 minutes per training session. HIT Training could also be suitable for athletes looking for a new muscle stimulus if they stagnate with their previous training. HIT can be a welcome change that sets new growth impulses.

What advantages can HIT Training have?

HIT Training can have some advantages that distinguish it from other training systems. Below I list the advantages that proponents of HIT Training often mention:

It is not as time-consuming as other training methods with the same goals. You increase your training intensity: With HIT Training, you train with a high intensity that challenges your muscles to the maximum. This way, you can activate more muscle fibers and achieve more muscle growth. Increased release of anabolic hormones. What disadvantages could HIT Training have? HIT Training can also have disadvantages. Here are some disadvantages that are often mentioned:

With HIT Training, you train with very high weights. The training can be stressful for your muscle-tendon unit and passive musculoskeletal system. You stress your body very much. If you do HIT Training too often or too long, you could overtax your body and possibly get into overloading and then overtraining with insufficient recovery.

How do you do HIT Training right?

If you want to try HIT Training, you should pay attention to some things.

Warm up thoroughly

• Perform a general warm-up and then work your way up to your training weight.

Choose the right exercises

• With HIT Training, you should focus mainly on basic exercises that stress several muscle groups simultaneously. As described below, you can combine these multi-joint exercises with isolation exercises as part of intensification techniques.

Choose the right weight

• With HIT Training, you should use the maximum weight you can move for 5 – 8 (10) repetitions. This corresponds to about (75%) 80 to 90% of your 1 RM. You should adjust the weight accordingly if you can do more or fewer repetitions. The weight should be so heavy that you can only do the last repetition with difficulty and under tension of all muscles.

Use intensification techniques to increase the stimulus

• With HIT Training, you use intensification techniques to increase the muscle stimulus and go beyond the momentary concentric muscle failure. These include, for example:
  • Drop sets, where you reduce the weight after failure (by about 30%) and do more repetitions.
  • Intensive repetitions, where you do some more repetitions after failure with the help of a partner.
  • Negative repetitions, where you slowly lower the weight but get help in the positive (concentric) phase (depending on the exercise, e.g., partner, changed body position).
  • Forced repetitions, where your partner helps you only as much as necessary to move the weight.
  • Rest-pause sets, where you pause briefly after failure (10 – 15 seconds) and then do some more repetitions.
  • Pre- and post-fatigue, where you do an isolation exercise before or after a basic exercise to fatigue the muscle even more.

Do only a few sets per muscle group

• You should do only a few sets per muscle group with HIT Training, as the intensity is very high. But the sets are usually extended by the intensification techniques so that you flatten your muscles.

Take enough rest between sets

• With HIT Training, you should rest enough between sets to recover and do the next exercise with full power. The rest length depends on the exercise, the weight and your fitness level, but should usually be between 2 and 3 minutes.

Is muscle failure necessary?

Short info in advance:

There is a relatively well-known principle for muscle activation. This principle is called Henneman’s size principle. The theory behind the principle describes how different motor units in our muscles are activated depending on how intense the contraction is. The principle is relatively well-known and somewhat established but not beyond question.³

But what are motor units? A motor unit consists of an alpha-motor neuron and all the muscle fibers innervated by its axon. An alpha-motor neuron is a nerve cell of the central nervous system (CNS), which innervates the skeletal muscle fibers and is responsible for muscle contraction. An axon is a long, tubular extension of the nerve cell and transmits electrical signals from the CNS to the muscles.³ The number of muscle fibers that a motor unit comprises can vary greatly. The eye muscles’ motor units contain only 6 muscle fibers. But there are also motor units, such as in the quadriceps, that comprise several hundred fibers.⁴

Now back to Henneman’s size principle. Imagine you are an experienced athlete who regularly does squats with a lot of weight. You do a light warm-up exercise, such as 20 bodyweight squats. With this low effort for you, the smallest motor units are activated first, which mainly supply the slow-twitch ST muscle fibers (ST, slow twitch).^cf.5,6 These fibers are designed for endurance activities and do not fatigue quickly. If you then move on to a more intense exercise, such as squats with a barbell of 50 kg, more ST fibers and additionally some fast-twitch FT muscle fibers are activated (FT, fast twitch).^cf.5,6 These FT fibers are faster and stronger than the ST fibers but also fatigue faster. At the latest, all motor units are activated when you have to exert a large part of your maximum strength, for example, to perform a heavy squat with a barbell of 100 kg.⁶ The range up to which more motor units can be switched depends on the muscle, probably between 60% and 85% of the maximum strength.⁵ Consequently, depending on the muscle, all motor units are probably involved when training with such intensities.⁵ it is still possible to generate more force, even though all units are involved. The CNS increases the force, increasing the rate of nerve impulses sent to the muscles.⁵

In general, FT muscle fibers also have the greatest potential for hypertrophy.⁷

Why training to exhaustion?

However, the activation of motor units described above does not always depend on the amount of load. As you approach exhaustion or muscle failure during a set, more and more motor units are involved, even with light and moderate weight, to continue the exercise. As a result, the FT fibers can also be involved in slow movements with a low weight. The prerequisite for this is the proximity to muscle failure or exhaustion.⁵ Because in strength training, depending on the weight, either smaller motor units are activated first; when they become tired, larger units are added. With heavy loads, many (or all) units are used from the start to handle the weight.⁵

The training to exhaustion is supposed to cause the activation of all motor units in the muscles, which could contribute to better training effects regarding hypertrophy and strength increase. This is especially true for training with light to moderate loads, because depending on the muscle, all motor units are already involved between 60% and 85% of the maximum strength.⁵ This assumption is based on the described Henneman’s principle. This means that in strength training, depending on the load, either smaller motor units are recruited first and then the larger units jump in as soon as the smaller ones fatigue or with higher weight more and more motor units are activated to handle the large load from the beginning.⁵

Scientific review articles have systematically investigated whether training for muscle failure is necessary for building strength and mass. The results of these studies are rather sobering. Studies conducted by Grgic et al. (2022) and Vieira et al. (2021) suggest that training for muscle failure, especially at higher loads, probably does not benefit building strength and mass.^5,8 However, it could be that training for muscle failure could help advanced strength athletes build mass.⁵ At lower loads (e.g. 30% of maximum strength), training for muscle failure could help build muscle strength and mass.⁵

If you want to learn more about programming strength training, click on the link. 😉

References

Mentzer, M. (1993). Heavy duty. M. Mentzer.

¹Nóbrega, S. R., Ugrinowitsch, C., Pintanel, L., Barcelos, C., & Libardi, C. A. (2018). Effect of resistance training to muscle failure vs. volitional interruption at high-and low-intensities on muscle mass and strength. The Journal of Strength & Conditioning Research, 32(1), 162-169.

²Nóbrega, S. R., & Libardi, C. A. (2016). Is resistance training to muscular failure necessary? Frontiers in physiology, 7, 10.

³Hug, F., Avrillon, S., Ibáñez, J., & Farina, D. (2023). Common synaptic input, synergies and size principle: Control of spinal motor neurons for movement generation. The Journal of Physiology, 601(1), 11-20.

⁴Brown, L. E. (2017). Strength training. Human Kinetics.

⁵Grgic, J., Schoenfeld, B. J., Orazem, J., & Sabol, F. (2022). Effects of resistance training performed to repetition failure or non-failure on muscular strength and hypertrophy: a systematic review and meta-analysis. Journal of sport and health science, 11(2), 202-211.

⁶Happ, Kevin A.; Behringer, Michael. (2022). Neuromuscular Electrical Stimulation Training vs. Conventional Strength Training: A Systematic Review and Meta-Analysis of the Effect on Strength Development. Journal of Strength and Conditioning Research 36(12):p 3527-3540

⁷Schoenfeld, B., Fisher, J., Grgic, J., Haun, C., Helms, E., Phillips, S., … & Vigotsky, A. (2021). Resistance training recommendations to maximize muscle hypertrophy in an athletic population: Position stand of the IUSCA. International Journal of Strength and Conditioning, 1(1).

⁸Vieira, A. F., Umpierre, D., Teodoro, J. L., Lisboa, S. C., Baroni, B. M., Izquierdo, M., & Cadore, E. L. (2021). Effects of resistance training performed to failure or not to failure on muscle strength, hypertrophy, and power output: a systematic review with meta-analysis. The Journal of Strength & Conditioning Research, 35(4), 1165-1175.