1. Conclusion
‘If I build muscle, my body will probably get stiff.’ Are you hesitating to do strength training because of this thought? Some people might think of stretching for flexibility and strength training for muscle strength as separate things.
Reading the research introduced here, it cannot be said that strength training always makes the body stiff. The results of a summary of multiple studies show that strength training increases the range of motion of joints.
However, this does not mean that ‘doing anything will make you flexible’ or that ‘stretching is no longer necessary.’ What kind of exercise was performed, by what kind of person, and what was measured? Reading that far reveals the relationship between strength training and flexibility.
Avoiding strength training because you are concerned about flexibility. Before doing that, let’s organize what we know from research.
2. What does ‘having a flexible body’ measure?
Raising your arms above your head, swinging your legs forward. The extent to which you can move a joint in these movements is the range of motion. In everyday language, we collectively call this ‘body flexibility,’ but shoulder movement and hip joint movement need to be checked separately.
For example, just knowing whether you can reach the floor when bending forward does not tell you how high you can raise your arms. Even in research, which joints are measured and by what methods varies, so there is not just one way to examine flexibility.
Also, feeling that muscles are stiff and the range in which you can move a joint are not the same thing. The paper discussed here examined the range of motion after continuing strength training. It is not a study that only investigated the feeling of tension immediately after exercise or the hardness of muscles when touched.
Even in strength training, you move your joints by raising your arms or squatting while resisting weight. The authors argue that moving while applying load to muscles in this way may lead to improvements in range of motion. However, the mechanism of improvement has not been fully elucidated.
‘Using muscles’ and ‘expanding the range of motion’ are not necessarily conflicting goals.
3. Strength training and joint range of motion from 55 studies
The paper featured is a systematic review and meta-analysis examining the relationship between strength training and range of motion by Alizadeh et al. They collected related studies under certain conditions and integrated the results to investigate trends. The subjects were 55 studies examining healthy people, with a total of 2,756 participants.
The exercises included were varied, such as free weights, machines, resistance bands, body weight, and Pilates. ‘Strength training’ does not mean only exercises that involve lifting heavy barbells were collected.
In the paper, the duration of the studies is introduced as 4 to 24 weeks, and the frequency as 2 to 5 times per week. These are the conditions used in the studies, and it does not mean that this frequency is recommended for everyone.
The results are easier to understand if you divide them by what they were compared to.
First, when integrating 52 studies compared to a control group, there was a clear difference in favor of strength training for improving range of motion. This does not mean that improvement was confirmed in all 52 studies, but it is the result of analyzing them together.
Next, in 7 studies comparing strength training and stretching, no clear difference in range of motion improvement was confirmed. In 4 studies comparing a combination of strength training and stretching versus stretching alone, no difference was confirmed either.
What is important here is that ‘no difference was found’ is different from ‘it was proven to have the same effect.’ Because the studies that can be compared are limited and there are differences in methods, the possibility remains that small differences were not captured.
By type of exercise, no clear improvement in range of motion was confirmed for bodyweight-only strength training. However, the authors also pointed out the small amount of data available for this analysis. One cannot judge that bodyweight exercise is meaningless based on this.
Furthermore, the exercise methods, joints measured, and measurement techniques vary from study to study. In comparisons with control groups, there were also signs of bias where studies reporting positive effects were more likely to be published. Therefore, it is necessary to consider the possibility that the results appear better than they actually are.
This research does not guarantee that everyone will become flexible in the same way. Even so, it serves as material to reconsider the assumption that ‘strength training impairs flexibility.’
4. Summary
What we should take away from this research is that strength training can be an option when considering flexibility. The results do not indicate that people who want to build muscle strength need to avoid strength training for fear of their bodies becoming stiff.
On the other hand, this does not mean that stretching is unnecessary. In their conclusion, the authors state that if range of motion increases with strength training using weights or other loads, adding stretching before or after strength training for the sake of flexibility may not necessarily be required. However, this is a perspective based on results comparing only range of motion. If you find stretching pleasant or feel that it loosens your body and makes it easier to move, there is no reason to stop.
Organizing where you find it difficult to move and what movements you want to make easier will clarify the purpose of choosing your exercise. Rather than applying the numbers from the research directly to your own routine, please consider a way to continue that suits your physical condition and experience.
If you find it difficult to choose on your own, you can also consult about how to choose and continue exercises at the personal gym & machine pilates studio fis.
If you have pain in your joints or lower back, or have a pre-existing medical condition, please consult a medical institution before starting exercise. Do not endure pain while trying to increase your range of motion during exercise, and consult a medical institution if pain persists.
Before thinking ‘strength training or flexibility,’ know that there is a possibility of aiming for both. That will be a new clue when choosing your exercise.
Supervision: Trainer Nishiyama (fis.osaka Esaka Store)
Qualifications: Physical Therapist (National Qualification) / JATI-Certified Training Instructor / Health Exercise Practice Instructor
For the instructor’s background, please see Trainer Nishiyama’s Profile.
