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EricT · 04-01-2007, 03:10 PM

Behm, D. G., Button, D. C., & Butt, J. C. (2001). Factors affecting force loss with prolonged stretching. Canadian Journal of Applied Physiology, 26, 262-272.

This study evaluated the phenomenon of force loss after prolonged static and passive stretching. Ss (N = 12) were tested before and 5-10 minutes after 20 minutes of static or passive stretching of the quadriceps. Six of the twelve Ss also performed a no-stretching (control) condition.

Following stretching, maximal voluntary contraction force decreased by 12%, while muscle activation increased by 2.8% and inactivation increased by 20.2%. It was suggested that strength loss after stretching is affected more by muscle inactivation than changes in muscle elasticity.

Implication. Too much stretching decreases force production. The value of stretching before athletic performances, particularly those involving strength or the production of large forces, should be questioned.
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Nelson, A. G., & Kokkonen, J. (2001). Acute ballistic muscle stretching inhibits maximal strength performance. Research Quarterly for Exercise and Sport, 72, 415-419.

Male (N = 11) and female (N = 11) physical education class students were tested for knee flexion and extension strength (1 RM) on two days. One test was preceded by quiet sitting, while the other was preceded by active and passive ballistic stretching of the hip, thigh, and calf muscles.

Stretching increased hip flexibility as measured by a sit-and-reach test. Knee extension and flexion strength was significantly less after stretching than after no stretching.

Implication. A thorough bout of stretching reduces the strength of the muscles stretched.
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STRETCHING REDUCES PERFORMANCE CAPABILITY
Evetovich, T. K., Nauman, N. J., Conley, D. S., & Todd, J. B. (2003). The effect of static stretching of the biceps brachii on torque, electromyography, and mechanomyography. Medicine and Science in Sports and Exercise, 35(5), Supplement abstract 2057.

Adult Ss (M = 10; F = 8) performed maximal isokinetic (30 and 270 deg/sec) forearm flexion strength tests on two occasions while EMG and MMG measures were registered. Ss were randomly assigned to stretching and non-stretching protocols before testing.

Stretching significantly reduced torque. MMG amplitudes were greater for stretching than non-stretching while EMG amplitudes were similar.

Implication. "These results indicated that a greater ability to produce torque without prior stretching is related to the musculotendinous stiffness of the muscle rather than the number of motor units activated. This suggests that performing activities that reduce muscle stiffness (such as stretching or warming up) may be detrimental to performance" (p. 370).
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STRETCHING REDUCES THROWING ABILITY
Noffal, G. J., Knudson, D., & Brown, L. (2004). Effects of stretching the upper limb on throwing speed and isokinetic shoulder torques. Medicine and Science in Sports and Exercise, 36(5), Supplement abstract 937.

This study determined the effects of static stretching of upper limb muscles on overarm throwing speed and isokinetic torque of shoulder internal rotators at two velocities (3.14 and 5.24 rad/s). Ss (N = 40) were randomly assigned into control and stretching groups. The experimental protocol consisted of two test sessions scheduled a week apart. Ss in the experimental group performed static stretching (S) exercises with their dominant limb in one session and no stretching (NS) in the other. Ss in the control group did not stretch in either of their two sessions. Following warm-up and S or NS, Ss were tested for throwing speed and concentric isokinetic torque of the shoulder internal rotation musculature at two velocities. Throwing speed was measured with a radar gun and shoulder internal rotation torques were measured with an isokinetic dynamometer. Speed and torque were compared.

Significant interactions were found for throwing speed and isokinetic torque at 3.14 rad/s (but not for isokinetic torque at 5.24 rad/s). Stretching reduced throwing velocity and shoulder isokinetic torque at the slower isokinetic speed.

Implication. Static stretching of the arm before a high speed movement, such as throwing, reduces subsequent throwing velocity. Stretching should not be part of a throwing or pitching warm-up.
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STATIC STRETCHING IMPAIRS POWER AND STRENGTH PERFORMANCE
Fry, A. C., McLellan, E., Weiss, L. W., & Rosato, F. D. (2003). The effects of static stretching on power and velocity during the bench press exercise. Medicine and Science in Sports and Exercise, 35(5), Supplement abstract 1460.

High school athletes (N = 40) were tested for bench press 1 RM at one session. In two other sessions, a general and exercise-specific warm-up, and a maximum velocity bench press at 85% 1 RM were performed. Static stretching was randomly implemented immediately before the tested lift in either session 2 or 3.

Static stretching significantly impaired bench press mean power and mean velocity.

Implication. Static stretching in close proximity to maximum power and strength activities has a detrimental effect on performance.
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TOO MUCH FLEXIBILITY CAN BE DETRIMENTAL TO RUNNING ECONOMY
Jones, A. M. (2002). Running economy is negatively related to sit-and-reach test performance in international-standard distance runners. International Journal of Sports Medicine, 23, 40-43.

The relationship between running economy and lower body flexibility were determined in international standard male distance runners (N = 34). Ss performed an incremental treadmill test to determine physiological attributes and the sit-and-reach test to measure lower body flexibility. Running speeds below lactate threshold were used to evaluate the relationship.

The results for running at 14, 15, and 16 km/hr were similar. There were no relationships between aerobic demand at 16 km/hr and age, height, body mass, or VO2max. However, there was a significant negative relationship between lower trunk flexibility and running economy. "Stiffer" athletes were more efficient runners. It was hypothesized that elastic energy was enhanced in muscles that were not overly stretched.

Implication. It is possible to have muscles that are too stretched. A loss in the elastic properties of muscle most probably results in a loss of energy production, and therefore movement efficiency, in running. It is possible to overdo stretching and flexibility training to the extent that it reduces performance potential.
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MUSCLE AND JOINT STIFFNESS IS ASSOCIATED WITH INCREASED RUNNING ECONOMY
Craib, M. W., Mitchell, V. A., Fields, K. B., Cooper, T. R., Hopewell, R., & Morgan, D. W. (1996). The association between flexibility and running economy in sub-elite male distance runners. Medicine and Science in Sports and Exercise, 28, 737-743.

The purpose of this study was to examine the association between nine measures of limb and trunk flexibility and running economy. Within a week before running economy assessment, and after 10 min of jogging at 3.13 m/sec, trained male sub-elite distance runners (N = 19) underwent two complete sets of lower limb and trunk flexibility assessments. Ss then completed two 10-minute running economy assessment sessions on consecutive days at 4.13 m/sec following two 30-minute sessions of treadmill accommodation at 4.13 m/sec.

Dorsiflexion (r = 0.65) and standing hip rotation (r = 0.53) were significantly associated with the mean aerobic demand of running, such that less flexible runners were more economical. Although speculative, these results suggest that inflexibility in certain areas of the musculoskeletal system may enhance running economy by increasing storage and return of elastic energy and minimizing the need for muscle-stabilizing activity.

Implication. Running economy needs natural tightness in lower leg muscles and connective tissues to maximize the storage and return of elastic energy and reduce the need for stabilizing activity.
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CONTRACT-RELAX STRETCHING IS BETTER THAN BALLISTIC STRETCHING FOR IMPROVING FLEXIBILITY
Wallin, D., Bjorn, E., Grahan, R. & Nordenborg, T. (1985). Improvement of muscle flexibility: A comparison between two techniques. The American Journal of Sports Medicine, 13, 263-268.

Males (N = 47) were formed into four groups. All groups trained three times per week using a modified contract-relax (CR) method or ballistic stretching. After 30 days, one of the CR groups (N = 10) trained once a week, another (N = 10) three times a week, and the third group (N = 10) five times a week. The fourth group (N = 17) trained with traditional ballistic stretching. After 30 days (14 training sessions), the ballistic group switched to the contract-relax method. Retests were performed after 60 days since commencement.

Once a week contract-relax stretching was enough to maintain flexibility. Training three to five times per week was necessary to increase flexibility. Ballistic stretching improved flexibility, but not as effectively as the contract-relax method. When the ballistic group switched to contract-relax, flexibility improved further and that group caught up to the others who had only been performing contract-relax activities.

Implication. Contract-relax (PNF) stretching is more effective for increasing flexibility than is ballistic stretching. Only one PNF session per week is needed to maintain flexibility.
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PROBLEMS WITH STRETCHING MYTHS AND THEORY
Wilkinson, M., & Williams, A. (2003). Too much of a good thing? Why increased joint flexibility may damage your distance performance. Peak Performance, 175, 5-6.

This is a well presented review article that looks at the research covering stretching and its effect on running economy. A number of statements concerning beliefs and theories regarding flexibility are made.

"There is little evidence to support the claim that non-pathological [naturally endowed] muscle tightness reduces running economy, so impairing performance" (p. 5).

"There is a growing body of evidence to suggest . . . that a lack of flexibility in certain areas of the body may be linked with increased running economy. And it is interesting to note that studies of competitive distance runners have shown them to be less flexible than non-runners" (p. 5)

Decreased flexibility in the trunk and hip prevented trunk rotation and hip turn-out while running, both restrictions improving running economy.

Decreased flexibility in the ankle (tightness in the calf and soleus muscles), and the lower back/hamstrings were associated with better running economy.

One explanation why a lack of flexibility actually increases running performance is that it reduces energy expenditure by enhancing elastic energy storage and return in the Achilles tendon and calf muscles.

"Previous work has suggested that elastic recoil of muscle and tendons can contribute 25-40% of the energy necessary for subsequent movements in a maximally stretched muscle [Cavagna,G. A., Saibene, F. P., & Margaria, R. (1964). Mechanical work in running. Journal of Applied Physiology, 19, 249-256; Cavagna, G. A., & Margaria, R. (1966). Mechanics of walking. Journal of Applied Physiology, 21, 271-278.] (p. 6).

"It is reasonable to suggest that inflexibility around the ankle joint would result in a greater relative stretch of the tight muscles and tendons, storing more elastic energy for subsequent recoil and reducing the active work of the muscles" (p. 6).

"Musculoskeletal tightness can also explain the beneficial effects of limited hip/trunk flexibility . . . Limited external hip rotation could enhance running economy by stabilizing the pelvic region at the time of foot impact. Since running occurs primarily in a forward direction, rotational motion is potentially energy-wasting as it does not contribute to forward movement" (p. 6) [Thus, actions in baseball that are aligned to produce forward momentum on a ball do not need to have above-natural flexibility. So exercises that stretch abdominal muscles laterally and forward and backward would only serve to reduce the elastic energy potential of a segmented action because other muscular contributions would be required to halt the "softened musculature" from moving.]

"There is a cut-off point where inflexibility ceases to be tightness within a normal range of motion and becomes excessive to the point of increasing injury risk. Clinically, excessive muscle tightness is believed to be an important cause of such injuries as muscle strains and inflammation of tendons" (p. 6)

Implication. ". . . while general stretching, designed to maintain existing levels of flexibility and muscle function, should remain an important aspect of every runner's warm-up and cool-down routines, improving flexibility beyond levels normal [natural] for runners is likely to impair rather than improve performance" (p. 6)