Whenever I see someone stretching before or after hard exercise, I worry that the person has gotten bad advice about training.
• You should not stretch before a competition because stretching weakens muscles.
• You should not stretch after hard exercise because stretching muscles that are already damaged by intense exercise delays recovery and increases risk for injury.
• You cannot lengthen muscles or tendons by stretching.
An extensive review of the scientific literature showed that the supposed benefits of stretching are highly controversial (Int J Sports Phys Ther, 2012 Feb; 7(1): 109-119).
Stretching Does Not Lengthen Muscles
You can make a muscle longer while you are stretching, but after you finish
stretching, the muscle returns to its former length. A review of 26 studies of
stretching for 3-8 weeks found that stretching did not elongate muscles or
tendons. The people were able to stretch further only because they learned to
tolerate more pain (Scand J Med Sci Sports, Mar
2018;28(3):794-806). People who stretch regularly, such as gymnasts and people
who do yoga, can stretch further than non-stretchers because they can tolerate
more pain or they have less pain while they stretch (Scan j
Med & Sci in Sports, Feb 2010;20(1):136-144). Stretching a
muscle pulls on nerve fibers in the muscle to cause pain, so you stop stretching
when it hurts. When a person is given an anesthetic, he can stretch much
further because he feels less pain. Regular stretchers stretch so often that
they feel pain later than non-stretchers do and they learn to tolerate more
pain when they stretch. If muscles did remain stretched, stretching would harm
you because the overstretched muscle would lose its elasticity and be much
weaker. Placing animals in muscle-stretching casts for several weeks can cause
the muscles to grow extra units called sarcomeres, but muscles return to their
original length soon after the cast is removed.
Stretching Does Not Prevent Sports Injuries
Muscles and tendons tear when the force applied to them is greater than their
inherent strength, so anything that makes a muscle stronger helps to prevent
injuries. Stretching does not strengthen muscles so it does not prevent
injuries such as shin splints, bone stress fractures, sprains or strains (Research
in Sports Medicine, Dec 2, 2016;25(1):78-90).
Stretching Does Not Prevent Delayed Onset Muscle
Soreness (DOMS)
A review of 12 studies published over the last 25 years shows that stretching
does not prevent delayed
onset muscle soreness (DOMS), soreness that occurs eight to 24 hours after
you exercise vigorously (The British Journal of Sports Medicine,
December 2011; 45:15 1249-1250). Researchers in Australia reviewed five
studies, involving 77 subjects, to show that stretching does not prevent
next-day muscle soreness (British Medical Journal, December
2007; 325:468-70 and 451-2). To enlarge a muscle and make it stronger, you have
to put enough force on it to damage that muscle, so proper training requires some
degree of muscle soreness on the day after an intense workout. Athletes train
by taking a hard workout, feeling sore the next day, and then taking easy
workouts for as many days as it takes for the soreness to go away. Since
stretching does not reduce muscle soreness, it will not help you to recover
faster from hard exercise. The best way to recover from exhausting competition
is to move with little pressure on muscles, such as cycling on a stationary
bicycle (American Journal of Physical Medicine & Rehabilitation,
June 2007).
How Muscles Move Your Body
Every muscle in your body is made up of thousands of individual fibers. Each
muscle fiber is composed of sarcomeres, repeated blocks lined up end-to-end to
form rope-like fibers. Muscles move your body by contracting which shortens
each muscle fiber. Muscles do not shorten (contract) equally throughout their
lengths. Muscles contract only at each of thousands of sarcomeres. It is the
cumulative shortening of thousands of sarcomeres that shorten fibers to make
muscles contract and move your body. A sarcomere contains two proteins: actin
and myosin. The actin proteins line up between myosin proteins above and below
them. The actins slide toward each other to shorten the sarcomere. When
thousands of sarcomeres shorten together at the same time, the entire muscle
contracts.
Stretching Before Exercising Weakens Muscles
Stretching before competition and training weakens muscles. Elite college
sprinters were timed in 20 meter sprints, with and without prior multiple
30-second stretches of their leg muscles. Both active and passive stretching
slowed them down (Journal of Sports Science, May 2005). Stretching prevents
you from lifting your heaviest weights or running your fastest miles. It limits
how high you can jump, and how fast you can run (Scand J Med Sci Sports,
2013 Mar;23(2):131-48; J Strength Cond Res, 2013,
Apr;27(4):973-7). Stretching weakens muscles temporarily by almost 5.5 percent.
The longer you hold the stretch, the more strength you lose. Holding a stretch
for more than 90 seconds markedly reduces strength in that muscle. Stretching
reduces power: how hard you can hit a baseball or tennis ball, or how fast you
can swim, run or pedal. When you stretch a muscle, you pull on the muscle
fibers and stretch apart each fiber at the thousands of Z lines between the
sarcomeres. This damage occurs only at the Z lines throughout the length of the
muscle fiber, to weaken the entire muscle. On the other hand, warming up makes
muscles more pliable, helps you to run faster and lift heavier, and helps to
prevent injuries.
Stretching Does Not “Warm Up” Muscles
Stretching can never be considered “warming up”. Holding a muscle
contraction does not generate much heat and therefore does not warm up muscles.
Warm up by starting out your exercise slowly and gradually increasing the
intensity. This raises muscle temperature to make muscles more pliable and
resistant to injury. Since almost 80 percent of the energy used to power
muscles is lost as heat, you must contract and relax muscles continuously to
generate the heat necessary to raise muscle temperature. Warming up before you
exercise helps to prevent injuries and lets you jump higher, run faster, lift
heavier or throw further. Your warm-up should involve the same muscles and
motions you plan to use in your sport. For example, before you start to run
very fast, do a series of runs of gradually-increasing intensity to increase
the circulation of blood to the muscles you will be using. If you decide to
continue stretching even after you have read all of my reasons not to, be sure
to warm up first; do not stretch cold muscles.
Prolonged Stretching Limits the Ability of
Muscles to Store Energy
Muscles are like rubber bands. They stretch and contract with each muscle
movement. This constant stretching and contracting stores energy. For example,
when you run, you land on your foot and the muscle stops contracting suddenly.
The force of your foot striking the ground is stored in your muscles and
tendons and this energy is released immediately to drive you forward. Your foot
hits the ground with a force equal to three times your body weight when you run
at a pace of six minutes per mile. Up to 70 percent of the force of your foot
strike is stored in your Achilles tendon and other tendons. This energy is
released by your muscles and tendons to drive you forward for your next step.
Stretching decreases the amount of energy you can store in muscles and tendons
and therefore weakens you and you have less stored energy to drive you forward,
so you have to slow down.
Contracting Stretched Muscles May Make Them
Stronger
Athletes can become stronger by lengthening their tendons before they contract
them. The longer a tendon, the greater the torque the muscle can put on a joint
and the more force it can generate to make you faster and stronger. Passive
stretches do not do this. It is more effective to try proprioceptive
neuromuscular facilitation (PNF), in which the athlete stretches his tendons
and then tries to contract the muscles from the lengthened position. Gymnasts
have been shown to increase their flexibility more after PNF stretching than
after static stretching (Journal of Sports Medicine and Fitness,
December 2014). Many athletes incorporate plyometrics into their training
programs. For example, they jump off a series of steps consecutively. Their leg
tendons are stretched when they land and they contract their muscles to do
their next jump. However, this has been shown to increase their chances of
injury.
Summing Up
Stretching offers little benefit to regular exercisers. There is some evidence that stretching a contracted muscle may offer a competitive athlete more power when that muscle is contracted, but stretching contracted muscles may increase susceptibility for injuries. Activities such as yoga that involve stretching motions can be beneficial and enjoyable, but they should not be used just before or just after a competition or session of hard exercise.
Checked 7/27/23
