Andrew Hamilton looks at the recent research on Kettlebell training for sports performance: how effective is it and can the use of Kettlebells be superior to conventional weight training? MORE
PNF, dynamic or static stretching – which is best for athletes?
Recent research has shown that some types of pre-exercise stretching may not only fail to enhance performance, but can also be counter-productive. However, as James Marshall explains, that doesn’t mean that you shouldn’t be stretching – you just have to stretch appropriately
Practice and research shows that the components of stretching are as varied as other training principles such as speed or strength. But all too often, stretching is either just tagged on to other forms of training, or overlooked completely. And repeating the same stretching routine day in, day out inevitably gets you the same results. However, adding a variety of stretches and altering the types of stretching that you do at different times of day, time of season, or time of year should enable you to improve your flexibility and your performance.
Is stretching is bad for you?
I’ve recently had this comment thrown at me by coaches and athletes alike. As is often the case, information can be misinterpreted or applied in the wrong context (with the best of intentions) and then becomes dogma – for example ‘weight training makes you slow’. There has been a lot of research in recent years that has shown that static stretching as part of a warm-up may not improve performance, and may actually inhibit speed and power activities(1). But some athletes and coaches have extrapolated these findings to conclude that all stretching is bad for you at any time. In fact, there may be a clue in the phrase ‘warm-up’ as to what you are supposed to do! We will examine this later.
In the 1960s, martial artists from the East who came to Britain did warm-ups with little or no static stretching, but lots of movements. At the same time, Eastern European coaches were getting their athletes to do lots of movements in their warm-ups. Anecdotally, having worked in the fitness industry for eight years in the 1990s, I suspect the fad for doing a warm-up then stretches, and then the workout, came from gym-based exercise courses. I was always asking my fitness staff why they prescribed warming up on an exercise bike for 5 minutes, and then 5 minutes of static stretches, then run on a treadmill for 20 minutes, rather than simply walk, jog and then run on a treadmill!
Now the wheel has turned full circle and researchers are confirming what experienced coaches from different countries have been practicing for years. So, if static stretching is not best performed in the warm-up, does that mean that it’s bad for you? If acute stretching in the warm-up does not prevent injury and can lead to an immediate performance decrement, does chronic stretching and improved flexibility prevent injury in the long term and improve performance(2)?
Studies looking at the benefits of regular stretching have found the opposite effects to that of acute stretching before an activity. These benefits include:
- A possible decrease in the likelihood of injury(3);
- An increase in muscular force and power;
- A possible increase in sprinting speed(4).
The improvements may only be mild (approximately 2-5%) but in athletic performance terms, very significant. All three areas are obviously very important to most athletes, so developing flexibility should assume a corresponding importance in an athlete’s training programme. However, the question may arise of how can you fit it all in? Time constraints may hamper your efforts, and flexibility training should not necessarily replace your strength or endurance and especially not your skills training. But training smarter and looking at the time of day and type of stretching may allow you to reap benefits without additional training.
Time of day
The body’s ability to stretch also changes throughout the day, and so the type of stretching you do should change too. One study of healthy 24-year-old males measured patella tendon stiffness in the morning and in the evening (5). Tendon stiffness was found to decrease by 20% at 6pm compared to 8am. This should mean that the evening is a better time of day to work on developmental flexibility, as the tendons are more compliant. However, no mention was made in the study of the subject’s current level of flexibility or exercise status, including stretching routines. The results may have been different in another population who had more or less exposure to flexibility routines.
Why are tendons less stiff in the evening? It could be down to an increase in body temperature, increased movement patterns during the day, or increased testosterone and cortisol levels that tend to peak later in the day and can influence tendon compliance(6).
Studies looking at the muscle force contraction or tendon compliance at different times of day have measured the skin temperature changes that occur naturally, and compared them with artificially induced temperature changes by external means.
In a study looking at peak power contractions at 7am and 6pm, naturally occurring skin temperature changes were low (2.6C) compared to studies looking at externally induced temperature changes (around 10C), but the evening power contractions were still as high(7). This led the authors to surmise that skin temperature changes were not responsible for the evening muscle power being higher because the results appeared to be similar whether the temperature change was 2.6C or 10C. Another study tried looking at external methods of temperature change – ice packs and hot packs – but found no change in tendon stiffness as a result(8).
While temperature changes in the muscle and tendon may influence compliance slightly, it is more likely that movement and hormonal changes lie behind the greater evening tendon compliance. The reasons why increased hormones affect tendon compliance are not yet clear, but there does seem to be a link. However, although the increased movement explanation may not seem ground breaking, just try touching your toes when you have just got out of bed in the morning, or have been sat in a car for a couple of hours, compared to when you have been moving around all afternoon.
Type of stretching
If tendons are more compliant in the evening, then this is when your developmental stretching should take place. But what about first thing in the morning? You get out of bed, you’re stiff, and ignoring all circadian rhythm advice (because you have to work) you are intending to train before 8am. We have seen that movement is likely to increase tendon compliance, so movement type or ballistic stretches are best performed in the morning or immediately before training. These ballistic stretches may seem like heresy, but performed in a controlled manner, are a way of increasing range of movement (ROM) effectively, without an acute detriment to performance.
A study on male and female college basketball players compared the effects of static stretching versus ballistic stretching versus no stretching in the warm-up on vertical jump (VJ) performance after 20 minutes of playing(9). The authors delayed the VJ test for 20 minutes, because that is when improvements in power are most needed – in the middle of the game, rather than before the start.
The static stretches were held for 30 seconds, whereas the ballistic stretches were in the same position but consisted of small bounces at the end of the ROM in time to a metronome set at 60 beats per minute. Many athletes will have been told not to bounce when stretching, but there is a difference between small controlled movements and flinging your limbs around wildly beyond your normal ROM! The authors of this study could find no evidence that ballistic stretching was harmful.
An example of ballistic stretching for the quadriceps would be to lie on your front and pull one foot towards your buttocks with both hands then pull your heel into your bum about another 1cm and release, repeating the pull/release sequence for 30 seconds. This is assuming that you can comfortably perform this stretch in a static position and that you never try and go beyond your normal ROM, especially first thing in the morning.
Dynamic stretching can take place first thing in the morning too and consists of more circular or action-orientated movements, which mobilise joints. A 10-minute routine (see box 1) before breakfast that replicates movements found in your sport or in your fitness training sessions will ‘kick start’ your mobility for the day. Rather than wait for your body to become mobile throughout the day, a structured session can fast track this progress. Box 2 shows a sample routine for a footballer.
If ballistic and dynamic stretching are useful first thing in the morning and pre-workouts, what about post-workouts and during the evening? Two main types of stretching are useful here. The first is commonly known now as proprioceptive neuromuscular facilitation stretching (PNF) but is also known as isometric stretching(10). The second is static stretching and is most commonly used for developmental stretching.
Two interesting studies have compared the two different methods of stretching on hamstring flexibility. The first compared static stretching, self-stretching, PNF and a control group (who did no stretching)(11). After four weeks of a 30-second stretch three times a week for four weeks, only the static stretching group showed an increase in hamstring ROM compared to the control group.
The second study compared 5-minute stretching protocols from rest and after 60 minutes of exercise(12). This study showed that PNF stretching was effective in improving acute hamstring flexibility after exercise, whereas static stretching was not effective.
PNF stretching can be used post-workout or as a separate flexibility session, but it is probably more effective immediately after exercise. However, any method that requires isometric contraction can also cause fatigue as the muscle is working, so care should be taken when considering how much PNF stretching to do. One stretch per muscle group would be enough. PNF stretching could be done after any strength training session, or on the same day, but not on alternate days between strength training sessions otherwise those muscles will not be allowed sufficient time to recover before the next strength training session.
To start with, try holding the isometric contraction for 2-3 seconds then relax and stretch for 10-15 seconds and repeat two to five times. Try to perform the stretch as soon as you have finished the muscle contraction, preferably within one second. Make progress by holding the contraction for up to 10 seconds and the stretch for up to 30 seconds. You can repeat this up to five times, but this is quite a lot of work for your muscles, which then becomes very time consuming. If time is a limiting factor, you can stretch two or three muscle groups at each workout, and then rotate to different ones throughout the week.
This is perhaps the safest and least fatiguing of all stretching methods. As such, it is ideal for use on rest days or after fatiguing workouts, or as part of a relaxation routine. It is best done in the later part of the day when tendon compliance is at its greatest. It shouldn’t be done immediately before performance or competition, unless there are specific tight areas that you wish to release. Static stretching should be performed in a warm, comfortable, preferably quiet, environment, to allow full relaxation of the muscles. Thursday night at 9pm sat in a puddle on a rugby training pitch in December, is possibly not the optimal environment for developing flexibility!
Perform each stretch slowly until you cannot reach any further. Breathe in and out slowly, and try to stretch a little bit further, hold this position for another 25 seconds, relax and then repeat again. Concentrate on releasing all tension within the muscle that you are stretching to allow a greater ROM. Because you have to relax your muscles, you may find that you are mentally relaxing too. This is another benefit of performing static stretching at the end of the day for many athletes. Try to match stretches for the left and right side of your body and also the front and back. For example, if you perform two stretches for the hamstrings, then do two for the quadriceps. Variety within stretching is as important as for any other training method, so think about two to four stretches for each muscle group that you can rotate between stretching sessions.
Doing the same stretching routines all the time and at the wrong time will lead at best to maintenance of your current levels, but at worst to a short-term performance decline and possibly staleness. An awareness that increased flexibility can lead to long-term performance improvements, and less likelihood of injury, is a good incentive to put time aside to stretch. By matching the type of stretching you do to time of day you do it, you can improve your performance by working with your body and not against it. If you don’t have time to do additional stretching routines in the day, simply performing the right type of stretching within your workout will help you improve performance.
- Clinical J of Sports Med 2004; 14(5):267-273
- Medi and Sci of Sports and Exerc 2004;36(3):371-378
- Am J of Sports Med 1999; 27(2):173-176
- The Physician and Sportsmedicine 2005; 33(3)
- Muscle and Nerve 2006; 792-800
- Life Sciences 2003; 73:349-358
- M&N 1999; 1380-1387
- Clinical Biomechanics 2005; 20:291-300
- JSCR 2006; 20(4):799-803
- Stretching Scientifically 2003; Stadion Pub
- JSCR 2005; 19 (1):27-32
- JSCR 2003; 17 (3):489-492