Some readers may think that weight training
and flexibility training are incompatible, that by lifting heavy weights their flexibility will decrease. This is a myth. Research in the 60s and 70s proved that correctly performed resistance exercise does not negatively affect flexibility (Alter, 1996. The Science of Flexibility, Human Kinetics, p151). It is possible to shorten muscle length and therefore decrease flexibility by performing many contractions within a decreased range of motion; however, I believe it is safe to say that most resistance exercises performed with good technique through a full range of motion will not reduce flexibility. In fact, in this article I will go a step further and argue that certain types of resistance training can actually increase flexibility.
The first piece of research showing that resistance training increases flexibility comes from the University of Sao Paulo, Brazil. Researchers Aline Barbosa et al (Journal of Strength and Conditioning Research, 2002, 16(1), pp14-18.) set up a 10-week study whereby two groups of elderly women were assessed on the sit-and-reach flexibility test. During the 10-week period, the training group of 11 elderly women followed a three times a week strength programme. Each workout consisted of the following exercises, all using resistance machines: chest press, seated row, shoulder press, seated biceps curl, seated triceps press, leg press, calf press, ab crunch. Subjects were correctly supervised for technique during the programme. The women performed no flexibility exercises as part of the training programme. The control group of eight women of similar age, height and weight performed no training during the 10 weeks. The results were as follows:
These results show that the training group had significantly improved their sit-and-reach score, whereas the control group showed no change.
The conclusion from this study was that, without performing any flexibility exercises, a regular series of strength exercises could improve the flexibility of elderly women as measured by the sit-and-reach test.
Meanwhile, in Kentucky
| ||Training Group ||Control Group
|Initial Sit-and-Reach ||30.4 cm (6.0) ||33.8 cm ( 6.6)
|Final Sit-and-Reach ||34.4 cm (6.6) ||33.1 cm ( 5.9)
This is an interesting finding, an unexpected adaptation to strength training. There are limitations to the study that need to be considered. Firstly, all the subjects were over 60 years old and while they were healthy had no track record of fitness training
. It could be that for this type of adult, any kind of activity would be enough to promote flexibility improvement. A young, healthy adult may not respond in the same way to a general strength programme. Secondly, the sit-and-reach test itself only measures spine and hip flexion and while it is a common test, it is quite non-specific. (See Alter, 2002 p269 for an explanation.)
A second study, also with elderly subjects (age range 55-83 years), but using specific range-of-motion tests for the neck, shoulder, hip, knee and ankle assessed the effect of using resistance to improve flexibility. This group of researchers from Kentucky, USA, studied 43 subjects split into two groups. (Swank et al, Journal of Strength and Conditioning, 2003, 17(2), 374-378.) Both groups followed 10 weeks of three times a week body recall classes. This exercise routine was specifically designed to be a pain-free, rhythmic workout to promote health and fitness and is franchised across the US. The difference between the two groups was that one used hand and ankle weights while performing the classes and the other group use body weight alone.
The findings of this study were that even though the resistance group only used light weights (1-3 lbs), they significantly increased their flexibility more than the bodyweight group after the 10-week exercise programme on five out of 10 measures of flexibility â€“ neck rotation left and right, hip extension, knee flexion and ankle dorsiflexion. The researchers concluded that because the exercises in the classes were performed through full joint range of motion, the increased resistance promoted extra flexibility adaptation.
The conclusion from these two studies (admitting the limitation of the age of the subjects) is that resistance training, which involves dynamic movements through a full range of joint motion, can improve flexibility as measured by maximum range of movement during a passive stretch (a passive stretch is one where the limb is moved by an external force, eg tester or gravity).
Anecdotally, simply by observing elite weightlifters one can see that this must be true. The range of motion these athletes display in the ankle, knee, hip and shoulder joints is excellent to perform movements such as the full snatch with correct technique.
And in the Soviet Union
Documented support for this idea with young athletic subjects comes from Iashvili (1983, Soviet Sports Review 18(1), cited in Alter 1996), who discussed how active stretching combined with strength exercises can reduce the gap between the passive range of motion and the active range of motion. The passive range of motion, as noted above, is the stretch produced by an external force or person and is usually greater than the active range of motion, which is the stretch one can generate oneself using the opposing muscle group strength.
For example, imagine stretching the hamstrings by lying on your back and lifting the leg with the quadriceps and hip flexors only and then by pulling with your arms. You will most likely increase the stretch in the hamstrings by pulling with the arms compared to using the muscles only.
Iashvili's findings were that by following an active stretching programme combined with strength, athletes could reduce the passive/active deficit, which he claimed was correlated with athletic performance. It would seem logical that the range of motion athletes can generate themselves has a greater relationship with performance than the range resulting from an external force.
Explaining how resistance training can increase flexibility is more difficult. In fact, the adaptations to flexibility training is one of the least understood areas of sports science research. Interestingly, the textbook by Alter referenced earlier in this article, while discussing many aspects of flexibility, does not contain a single chapter on the adaptations to flexibility training. A paper by Magnusson (Scandinavian Journal of Medicine and Science in Sports 1998, 8, pp65-77) is more illuminating. He discusses the research his team from Copenhagen, Denmark, have performed using a specifically designed apparatus to measure the passive force response of the hamstring muscle to an imposed stretch.
The key findings from their research are:
* Holding a static stretch for up to 45 seconds produces a relaxation effect on the muscle, reducing the resistance within the muscle to the stretch â€“ this is the expected viscoelastic response to strain. The relaxation effect only lasted 1 hour
* Long-term adaptation to a daily static stretching routine showed that the resistance within the muscle to the stretch did not decrease for a given angle, but the maximum joint range of motion did increase. This suggests that flexibility training increases the stretch tolerance, ie the ability to withstand the sensation or force of the stretch.
* Subjects with low flexibility levels demonstrated a lower stretch tolerance and increased resistance to the stretch than subjects with good flexibility.
The relevance of these findings to the discussion of developing flexibility through strength training is that they show that the response of the muscle tendon unit to static stretching is unclear. Performing a stretch will relax and lengthen a muscle in the short term, but the development of flexibility in response to regular static stretching is not the result of chronic changes in muscle tendon resistance to stretch but a tolerance to the stretch itself. If this is the case, then it would seem dynamic or active stretching would be just as effective as static stretching and more relevant for athletic movements. If the muscle adaptation required for increased flexibility is to become more tolerant to being stretched, then logically to develop flexibility simply by taking a muscle through a full range of motion, inducing a stretch, is sufficient to stimulate increased flexibility.
The static hold/relaxation part of stretching seems less relevant. In addition, if less flexible subjects have increased stiffness (greater muscle resistance to the stretch), as the Magnusson research suggests, then maybe the benefit of adding weights to dynamic movements is that it enables greater range of motion due to the extra force applied to the muscle.
The last paragraph is my own hypothesis, supported by personal experience of increasing range of motion in athletes with tight shoulder joints using large-range dynamic movements with moderate weights. I believe that sports science may still have some way to go before we fully understand the mechanisms and most effective methods of developing flexibility. If any readers have knowledge of research with more information on the subject, I would be happy to hear from them. However, I can recommend with some conviction that resistance exercises and dynamic movements involving body weight, which take the joints through a full range of motion, will promote increased flexibility effectively. Another possibility as to why resistance training improves flexibility is that the muscle responds to the loading in the stretched position by adding more sarcomeres to the muscle fibre, thereby lengthening the muscle and increasing the maximum range of motion.