These two terms are often used synonymously when speaking about human movement but contrary to popular belief they are anything but the same.
Flexibility is the ability of connective tissue such as muscle, ligaments and tendons to lengthen. To train a muscle to become more flexible, the most common training method is static stretching; this involves stretching a muscle passively, by simply relaxing it and taking it to end Range Of Motion (ROM).
Mobility on the other hand is more of an active movement. Mobilising exercises are often dynamic in nature and initiated through controlled muscular contractions taking the muscles and joints through full ROM.
The main difference between mobility and flexibility is that in order to be mobile you should also have strength; being flexible on the other hand has very little to do with strength and in fact those individuals who are more flexible often tend to have poor muscular control and can sometimes be hypermobile. Being hypermobile unfortunately leaves you with an increased risk of strains, sprains and dislocations. It’s important for those that are naturally flexible to exercise caution when performing mobility and flexibility work and that you dictate a little more time, energy and focus to strengthening the muscles around the joints, ensuring safe levels of stability.
In order to be mobile, you also need strength, coordination and kinaesthetic awareness. An example of someone with great mobility would be a person with the ability to Barbell back squat 100 kilo through full range (ass to grass!). Someone with great flexibility may also be able to squat ass to grass but only with their own bodyweight, as soon as you add weight to the bar their technique will crumble. Someone with poor flexibility may be able to squat the 100kilo weight but their ROM will be restricted, only allowing them to make a shallow quarter squat depth.
Mobility and flexibility also have very different uses in our training. The Temple Training Movement Method (TTMM) uses both mobility and flexibility exercises during each workout but we always mobilise at the beginning of the workout as part of the warm-up process whereas we train flexibility at the end as part of the cooldown.
The mobilising phase is used at the start of our workout when you want to switch everything on. This is done by taking joints and muscles actively through ROM with specific movement patterns designed to free up the body via various fascial slings. These active movements are not held in end ROM, simply flow in and out of positions. You are not trying to increase overall ROM while mobilising, you are merely increasing blood flow and joint mobility while switching on the nervous system in preparation for the workout to come.
Flexibility is trained at the end of the workout when you want to slow things down, the reason is that flexibility involves taking muscles to end ROM and holding them statically in this stretched position to encourage them to lengthen; however this process also causes them to switch off. Ideal for down regulating the nervous system and lowering muscular tone so we can quickly return to a resting state and start the recovery process after a heavy workout. Disastrous if you are about to start caning it in the gym. Now you know the reasoning behind both ensure that you incorporate them into your workouts at the right time for the right purpose.