Historically, stretching has been considered an essential part of warm-ups, fitness and general health. However, over the past twenty years, this belief has been challenged, with some studies suggesting that static stretching performed just before a session or competition could impair performance such as strength, speed, power and balance. However, a closer analysis of these studies showed that if static stretches of less than 60 seconds per muscle group were incorporated into a warm-up involving dynamic activities, the possibility of significant alterations in performance was very low.
The effectiveness of stretching in improving range of motion (ROM) in the short- and long-term, in healthy people, is widely recognized. Nevertheless, in recent years, the debate has evolved as to whether stretching is the only method of improving joint ROM, with strength training emerging as a viable alternative. Indeed, several studies have suggested that strength training can induce similar ROM improvements to stretching. However, the type of specific resistance training (free weights, machine, bodyweight, Pilates) and its specific effect on joint mobility play a crucial role in these results. Considering the concept of specificity (angles, ROM, for examples), it is possible that exercises with a restricted ROM, such as certain bodyweight or machine exercises, do not improve mobility in the same way as those with free loads whose range of motion is complete.
Although many studies show that regular strength training can increase joint mobility, further analysis is needed to determine whether or not this improvement is similar to stretching. Furthermore, are the effects of training on joint amplitude moderated by variables such as gender or training level? If strength training can bring gains, will the addition of stretching bring further gains? What does the scientific literature say?
To answer these questions, researchers carried out a meta-analysis to compare the effects of resistance training, training based solely on stretching and training combining the two on joint ROM. The researchers analyzed the results of 55 studies. A total of 2,756 people aged between 10 and 70 took part in randomized, controlled longitudinal studies lasting from 4 to 24 weeks, with 2-5 weekly sessions at loads ranging from 40 to 110% of 1RM, with a before-and-after comparison of joint mobility.
In addition, the researchers also carried out sub-analyses according to participants' level of physical activity (sedentary and inactive vs. trained and active), gender (male vs. female vs. mixed), type of contraction (eccentric, concentric and isometric), type of exercise (body weight vs. free-load vs. machine vs. Pilates vs. elastic bands vs. mixed), and joint tested (elbow vs. hip vs. knee vs. shoulder vs. trunk vs. trunk and hip).
The main results of this meta-analysis show that resistance training (free weights and machines) significantly improves joint range of motion (moderate effect size). Only bodyweight training failed to improve joint mobility. What's more, these beneficial effects were no different from those obtained with training based solely on stretching, or with training combining strength training and stretching.
When the researchers analyzed these results in relation to the participants' level of activity, they found that sedentary and inactive people achieved the greatest improvements in range of motion compared to trained and active individuals. This is probably because the margin of progression for trained individuals is much smaller than for beginners. No significant differences were observed according to gender, type of contraction, age, duration or frequency of sessions.
The movements performed during strength training exercises are similar to those performed during dynamic stretching, but with an additional external load. Dynamic stretching is described as an action involving controlled movement through the joint active ROM. Exercises with free weights or machines (including Pilates exercises) generally allow the joints to reach their maximum amplitude, or at least the point of maximum discomfort, at a controlled pace. Conversely, some bodyweight exercises (e.g. push-ups) do not always allow maximum joint mobility. Thus, it's possible that the gains observed with resistance training may derive from both maximal ROM and additional external loading. These gains could be explained by the same adaptive mechanisms hypothesized to be behind the gains for dynamic stretching: neural, morphological and psychological factors. However, for neural and morphological factors, no clear consensus has been reached. On the other hand, there is considerable evidence on the impact of stretching on pain tolerance. External loading may accentuate these effects.
Resistance training with external loads can improve joint ROM, with no difference in results from training based solely on stretching or on a combination of strength training and stretching. Joint mobility gains and resistance training can both improve strength and help reduce the risk of injury. While resistance training can be beneficial for flexibility, stretching remains essential for many disciplines in the quest for extreme joint ranges. In some sports, stretching can also be used as a warm-up exercise. Or stretching could even be used as a relaxation method in many situations.
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