**4. Discussion**

It has been evidenced that the warm-up brings positive effects to the subsequent physical exercise, so it is very important to study it and understand how it can be manipulated according to the specificity of exercise training and performance. The purpose of this investigation aimed to analyze and discuss the main results of the literature regarding the effects of warm-up on force production, as well as to

analyze those responses during resistance training and maximal strength assessments. The scarcity of research on warm-up protocols in resistance training and strength performance is notorious. Nevertheless, it is possible to verify that the results obtained in most studies are positive. The use of warm-up causes enhancement of performance when external loads are used, especially when the intensity is high. However, more research should be carried out on this topic.

The selected articles of this review tend to focus on the effects that warm-up produces on resistance training, namely the effects on strength performance. Due to the scarcity of articles about the addressed issue, it was difficult to compare the different types and approaches of warm-ups. Moreover, it was also noticed that exercises were not the same in different studies, which also difficult outcomes analysis.

In the study of Rodrigues and collaborators, [23] three different types of warmup were compared: a general warm-up, a specific warm-up, and a warm-up through stretching, to understand whether it would influence maximal isokinetic training. The results reported that the three types of warm-up had no adverse effect or any type of improvement in acute muscle strength. However, it is important to highlight that the peak of concentric torque reported a lower value in the specific warm-up protocol when compared to the control group, which may mean that the use of a specific warm-up tends to reveal positive results when compared to the control group, which did not perform any type of warm-up.

The study by Ribeiro and Romanzini [25] aimed to compare the effects of three types of warm-ups on the performance of resistance training: a specific warm-up, an aerobic warm-up, and a combined warm-up of both, also using a control group. This study had the particularity of evaluating the performance using repetitions until failure, thus observing whether the conditions would affect resistance training. As in the abovementioned study, none of these conditions showed significant differences in resistance training, although no negative effects were observed after applying a warm-up. This study seems to suggest that the warm-up protocols used do not contribute to the development of strength.

Although the previous two studies have not found a significantly positive response in the strength assessment, the literature reported several benefits on the human body when considering the implementation of warm-up before resistance training [12]. In the study by Abad and his collaborators, [26] the aim was to understand if the implementation of a general warm-up before a specific warm-up would be beneficial when compared with a specific warm-up only. The tests were measured in the leg-press exercise, being evaluated by its 1RM. Two protocols were used in order to determine the effects of warm-up on training: combined warm-up (general with specific) and specific warm-up. The results of the combined warmup were higher values in the force production, in comparison with the specific warm-up. Considering the positive results of the tests, a combined warm-up would have more benefits than a specific warm-up.

Barroso and his collaborators, [29] purposed to understand the best intensity to use in the general warm-up before the specific warm-up. Thus, four combined warm-up protocols were performed, with different intensities and durations, which were compared with each other and with a control group, which performed only a specific warm-up, with no general warm-up. These researchers found that a general warm-up followed by a specific warm-up would be more beneficial to increase the strength when compared to a specific warm-up that reported lower results. The authors also suggested that when performing the aerobic component of general warm-up, it should be long lasting with low intensity for better results.

On the other hand, the results of Krzysztofik and Wilk [22] did not corroborate with the studies of Abad and his collaborators [26] and Barroso and

#### *Warming-Up for Resistance Training and Muscular Performance: A Narrative Review DOI: http://dx.doi.org/10.5772/intechopen.96075*

his collaborators [29]. This study aimed to compare a specific warm-up (named conditioning activity) with a general warm-up, performed before a bench press exercise. In this study, the specific warm-up was performed with a different exercise (plyometric push-ups) from the training exercise (in this case, bench press). The researchers concluded that the use of a specific warm-up had significant results in the strength assessment compared to the general warm-up. The outcomes showed improvement in the bench press exercise performance, being incongruent with the previously mentioned results.

Otherwise, Ribeiro and colleagues, [21] aimed to understand the best intensity to use when only a specific warm-up was performed. This study verified if three types of warm-ups would have an effect on strength training, and its protocols would use three types of external loads in the warm-up exercise: 40% of the training load, 80% of the training load, and the combination of the 40% and 80% of the training load. Positive effects in force production were found when warming-up with higher loads (80% of the training load) before the squat exercise training. The same authors also reported that, when performing a warm-up with low loads and repetitions, there was no effect on strength training performance.

Similar to Ribeiro and colleagues, [21] Minas and collaborators [24] evaluated a specific warm-up in their study. These authors, although also used the squat exercise in their study, used two different warm-ups. A protocol with a chain-loaded (as external weight) and another where it would be used only with the weight of the body, without any help from external loads. The aim of this study was to perceive the effect of another form of variable resistance in a warm-up compared to a warmup with only bodyweight. After applied the two defined protocols, it was concluded that using a chain-loaded weight as the body's external weight can enhance our results in the field of strength. Then, it is possible to notice that this study is in agreement with the previous one, although it cannot be directly compared. Both concluded that when using a warm-up with external loads to our body, the results tend to be better.

Sotiropoulos and his collaborators [28] carried out a study to determine the effects of a specific warm-up using low and moderate-intensity squats in the vertical jump. In his study, two warm-up protocols were performed using two different external loads (low and moderate), before performing the countermovement jump. Both protocols demonstrated to be effective when performed before the vertical jump, reporting significant results in the acute force production and the electromyographic activity, showing to be quite beneficial for the countermovement jump.

In the study of Chattong and his companions, [27] which aimed to investigate the potentiating effects of different levels of external resistance (weight vest) during box jumps in the vertical jump, five different warm-ups were assessed. The control condition was performed without any external load and then, the experimental warm-ups were performed with additional weight from 5% to 20% of bodyweight. In this study, the researchers concluded that no improvements in force production were found when increasing the load in the different warm-ups, not even any between using a vest or without it.

The study by Resende and his collaborators [30] aimed to analyze three different types of protocols, to understand their effect on the physical performance of paralympic powerlifting athletes. The protocols applied were: without warm-up, traditional warm-up and stretching warm-up. The results indicated by the researchers revealed that there were no significant differences when applying any of the protocols studied. Although the results did not show significant results, it is important to note that the participants were highly trained athletes and this might have triggered these results.

Gerard and his colleagues, [31] performed the following protocols: runningbased warm-up and strength-based warm-up to investigate the influence of two warm-up protocols on the neural and contractile parameters of the knee extensors. It was revealed a significant shortening of time to contract, while the other twitch parameters did not change significantly. Thus, they concluded that both protocols can influence strength training and muscle contraction during training.

After analyzing these studies, there is still controversy around the issue of warming. All studies included in this narrative review are relatively recent, but a consensus has not yet been reached, neither what is the best type of warming up that will have the best results on force production and strength performance. Further investigations should be developed to provide a consensus and clarify the subject. For future studies, it would be interesting to explore this topic a little more. We suggest to study the effect of warm-up on strength training, exploring different types of intensities, in order to achieve more robust and concrete results. The same studies should not be based on a single exercise, but rather deepen the study on several exercises performed in a sequence. It is true that, in a real training context, no single exercise is performed. For example, most resistance training includes more than one exercise and for different muscular groups. It would also be interesting to verify if it will be necessary to warm-up before each exercise and specifically for each exercise, or if the first warm-up before training is enough to guaranty better results during the entire training.
