The start of most race events, whether it be sprinting out of the starting blocks in the 200m dash or jockeying for position in the first 100 meters of a 1600m race requires strength, speed and power. Static stretching when performed greater than 45 seconds inhibits speed and power performance in sprint events such as the 100m dash. However, static stretching and its impact upon endurance performance has not been significantly studied, but has recently started to gain greater investigative attention, especially with its influence upon running economy.
The Economy of Running
Successful distance running performance, as stated by Joyner, is dependent upon the interrelationship of several variables, including a high maximal oxygen uptake (V̇o2max), the ability to sustain running pace at a high percentage of V̇o2max (fractional utilization of V̇o2max), and optimal running economy. Running economy, means efficiency; how efficient, in terms of energy conservation, a runner is during any given bout of running. Saunders, et al state that (taking body mass into consideration), runners with good running economy use less energy and therefore less oxygen than runners with poor economy at a given velocity. Ultimately, there is a strong correlation between running economy and distance running performance with running economy being a stronger predictor of performance outcome than maximal oxygen uptake in elite runners who have a similar aerobic capacity.
Tissue Stiffness and the Economy
Running economy is influenced by many variables such as, but not limited to, biomechanics and neuromuscular factors. Tissue stiffness, which is the ability of musculotendinous structures to absorb energy during the shock of landing and its transfer to push-off, has also been proposed to influence running economy:
A 2009 study in the Journal of Strength and Conditioning Research investigated the relationship between lower extremity flexibility and running economy. Eight collegiate distance runners had their flexibility measured using the standard sit-and-reach test, while running economy was recorded during an incremental maximal treadmill test at 10-km pace. Statistical analyses indicated a significant relationship between sit-and-reach scores and running economy at a given velocity.
A 2011 study presented in Medicine and Science in Sports and Exercise assessed whether the knee extensors and ankle plantar flexors length and flexibility are related to walking and running economy. Twenty-one male distance runners muscle and tendon length were measured by magnetic resonance imaging and oxygen uptake was measured at rest while seated, walking at 3 mph, and running at6 and 7 mph. Results showed that net VO2 (exercise VO2 – rest VO2) for walking and running at 6 and 7 mph was significantly related to Achilles tendon length but not Achilles tendon cross section. Quadriceps/patella tendon length was significantly related to running at 7 mph and approached significance for the 6 mph variable whereas increased flexibility of the plantar flexors was related to running at 7 mph. The authors state that these data support the premise that longer lower limb tendons (especially Achilles tendon) and less flexible lower limb joints are associated with improved running economy.
A 2002 study as presented in the International Journal of Sports Medicine investigated the relationship between running economy and lower body flexibility. Thirty-four elite male distance runners performed a treadmill test for the assessment of running economy, lactate threshold and VO2max, while the sit-and-reach test assessed general lower body and trunk flexibility. Running speeds below the lactate threshold explored the relationship between running economy and sit-and-reach test performance. Results showed that aerobic demand was not influenced by age, height, body mass, or VO2max. However, there was a highly significant relationship between aerobic demand and the sit-and-reach test score. These results suggest that the least flexible runners are also the most economical.
These studies suggest that less flexible distance runners, or those with ideal tissue stiffness tend to be more economical. Researchers postulate that stiffer musculo-tendinous structures reduce the aerobic demand of submaximal running by potentially facilitating a greater elastic energy return during the shortening phase of the stretch-shortening cycle. In other words, increased tissue stiffness in a runner is beneficial in order to utilize the stored elastic energy that occurs during the loading phase of stance; stiff tissue acts like a spring that facilitates propulsion during running.
While these studies support a direct relationship between tissue stiffness and running economy, additional research suggests an inverse relationship between tissue stiffness and static stretching. Static stretching is shown to decrease tissue stiffness, thus potentially inhibiting running economy and ultimately hampering performance.
Static Stretch and Endurance Performance
A review of literature was performed of the PubMed database as well as review of articles presented in 7 scientific journals using the keywords: static stretching, running economy, running performance, endurance perfoermance and tissue stiffness. An evaluation of findings is presented below:
A 2005 study presented in the Journal of Strength & Conditioning Research assessed knee flexion muscle strength-endurance e at 60 and 40% of body weight following either a static stretch regimen or a control group of no stretching. In a second experiment, a knee-flexion muscle strength-endurance exercise was performed at 50% body weight on 4 different days, with 2 tests following a no stretching regimen. For experiment 1, when exercise was performed at 60% of body weight, stretching significantly reduced muscle strength-endurance by 24%, and at 40% of body weight, it was reduced by 9%. For experiment 2, reliability was found to be high and muscle strength endurance was reduced by 28%. Researchers in this study declared that heavy static stretching exercises should be avoided prior to any activities requiring maximal muscle strength endurance.
These results presented a significant strength endurance loss although the testing was isolated to a single muscle group and was not performed with a specific sport activity. Questions are raised as to whether the results found in an isolated muscle test would carry over to muscular endurance required in an endurance running event.
In a similar study performed in 2008, presented in the Journal of Strength and Conditioning Research, two experiments were conducted to test the effect of the number of sets, and set duration and type of stretching on muscular endurance. For the first assessment, bench press endurance was evaluated (maximal number of repetitions) after static stretching comprising one set of 20 seconds, two sets of 20 seconds, and three sets of 20 seconds. In the second assessment, bench press endurance was evaluated (maximal number of repetitions) after static stretching comprising one set of 20 seconds, one set of 40 seconds, and proprioceptive neuromuscular facilitation stretching. The number of sets of stretching showed no effect on muscular endurance. However, significant reductions in muscular endurance were obtained as set duration increased as well as following the PNF activity.
The results of this study suggest that a decline in local muscle endurance is attributable to set duration and PNF activity; whereas, a low volume of static stretching does not seem to have a significant effect on muscular endurance. While this study shows a decline in muscular endurance with prolonged duration stretching, one has to question if these results would carry over to running endurance.
While the two previously presented studies assessed the effects of static stretching on local muscle endurance as performed in a non sport related activity, the following assessments measured the effects of static stretch upon running performance:
A 2009 study investigated the magnitude of relationship between sit-and-reach flexibility and running economy in collegiate distance runners (4 men and 4 women). Each subject’s flexibility was measured using the standard sit-and-reach test while running economy was recorded during a maximal treadmill test at 10 km pace. Statistical analyses indicated a significant relationship between sit-and-reach scores and running economy, as well as a significant gender difference in sit-and-reach scores. The significant relationship demonstrates that the less flexible distance runners tended to be more economical.
This 1996 study examined the association between nine measures of limb and trunk flexibility and running economy in which 19 well-trained male sub-elite distance runners completed two 10-min running economy assessment sessions on consecutive days following two 30-min sessions of treadmill running. Analysis revealed that ankle dorsiflexion and standing hip rotation were significantly associated with the mean aerobic demand of running, such that runners who were less flexible on these measures were more economical.
A 2014 study presented in the Journal of Strength Conditioning and Research investigated the effects of static stretching on 1-mile uphill run performance, electromyography (EMG), ground contact time, and flexibility. Ten trained male distance runners performed a 5 minute treadmill warm-up and either performed a series of 6 lower-body stretches for three 30 second repetitions or sat still for 10 minutes. Performance measures included: time to complete a 1-mile run under stretching and nonstretching conditions at a set incline of 5%. These results indicate that time to complete the run was significantly less in the nonstretching condition as compared with the stretching condition. Study findings indicate that static stretching decreases performance in short endurance bouts (∼8%) while increasing ground contact time and muscle activation.
A 2010 study as presented in the Journal of Strength and Conditioning Research investigated ten trained male distance runners engaged in a 60-minute treadmill run randomly under stretching (16 minutes of static stretching using 5 exercises for the major lower body muscle groups) or non-stretching conditions (16 minutes of quiet sitting) separated by at least 1 week. The run consisted of a 30-minute run at 65% V̇O2max followed by a 30-minute performance run where participants ran as far as possible without viewing distance or speed. Total calories expended were determined for the initial 30 minute run, whereas performance was measured as distance covered in the performance run. In this study, performance was significantly greater in the non-stretching versus the stretching condition, with significantly greater energy expenditure during the stretching compared with the nonstretching condition. These findings suggest that stretching before an endurance event may lower endurance performance and increase the energy cost of running.
These studies clearly indicate the impact of static stretching upon running performance, running economy and components of running economy including muscle activation, ground contact time, calorie expenditure, time to reach Vo2 max and blood lactate accumulation.
Additional investigations have shown that while static stretching clearly reduces tissue stiffness, the duration of that reduced stiffness may be of limited duration:
A study in 2009 showed that two 30 second bouts of static stretch were sufficient to induce a significant decrease in the passive musculotendinous stiffness of the plantar flexor muscles. However, these authors reported that although stiffness decreased immediately after 2 min, 4 min, and 8 min of SS, the effects of stretching disappeared within 10 min.
A study in 2013 suggests that static stretching for 5 min results in significantly increased range of motion over 30 min, but significant decreases in stiffness of the muscle-tendon unit returned to baseline levels within 5–10 min.
Mizuno et al showed that static stretch for 5 minutes at maximal dorsiflexion resulted in significantly increased range of motion that persisted for 30 min, but significant decreases in musculotendinous stiffness returned to baseline levels within 10 min.
A 2008 study showed that musculo-tendinous stiffness decreased immediately after 30 second bouts of passive stretching for 2, 4, and 8 total minutes. However, stiffness for the 2 minute condition returned to baseline within 10 minutes, whereas after 4 and 8 minutes of passive-stretching, conditions returned to baseline within 20 minutes. Overall, varying durations of passive stretching resulted in significant decreases in musculotendinous stiffness; however, these changes return to baseline levels within 10 to 20 minutes.
These studies indicate that while some studies show a negative impact of static stretching upon tissue stiffness and running economy, the impact may be of limited duration showing that activities greater than 10 minutes, and perhaps up to 20 minutes – depending on duration of stretch, may not be influenced by these detrimental effects.
The limited time of the effects of static stretch upon tissue stiffness may or may not have been a limiting factor on the results of this study:
A 2011 study in the Journal of Strength and Conditioning Research investigated the acute effects of static stretching on running economy and endurance performance in trained distance runners. Twelve long distance female runners performed 2 sessions of 60 minute treadmill runs following a randomly assigned static stretch protocol or quiet sitting. During the first 30 minutes, expired gases, heart rate, and rating of perceived exertion were recorded while the participant ran at 65% V̇o2max. During the final 30 minutes, distance covered, speed, heartrate and rating of perceived exertion were recorded while the participant attempted to cover as much distance as possible. These results showed that static stretch, as measured by sit and reach increased flexibility but had no effect on running economy, calorie expenditure, HR, or endurance performance. These findings indicated that stretching did not have an adverse effect on endurance performance in trained women.
Further studies have additionally shown limited impact of static stretching upon running economy:
A 2008 study in the Journal of Sports Sciences examined ten male runners who performed 10 minutes of treadmill running at 70% aerobic capacity before and after static stretching (40 seconds of eight different stretches repeated three times) and no stretching interventions. Respiratory gases were measured during the run bouts as well as measurements of LE mobility via a sit and reach test, isometric strength and counter-movement jumps before and after static stretch. Results indicate that oxygen uptake,energy expenditure and heart rate responses were not affected by the stretching intervention versus a significant increase in sit and reach mobility, as well as a decline in isometric strength and counter-movement jump height. These results suggest that prolonged static stretch does not influence running economy despite changes in neuromuscular function.
These results suggest that static stretching may not affect running economy at lower running speeds as presented by the 70% of aerobic capacity pace which is considered a jogging pace.
In addition, a 2014 study presented in the journal Plos One investigated participants in a 3km running time trial in which eleven recreational distance runners performed a) a constant speed running test without previous static stretching as well as a maximal incremental treadmill test; b) an anthropometric assessment and a constant speed running test with previous static stretch; c) a 3 km time trial familiarization on an outdoor 400-m track; d and e) two 3 km time trials, one with static stretch (experimental situation) and another without (control situation) previous static stretching. Sit-and-reach and drop jump tests were performed before the 3 km running time trial in the control situation and before and after stretching exercises in the static stretch condition. Running economy, stride parameters, and electromyographic activity (EMG) of vastus medialis, biceps femoris and gastrocnemius medialis were measured during the constant speed tests. The overall running time did not change with the conditions, but the first 100 meters was completed at a significantly lower velocity after static stretch. Surprisingly, static stretch did not modify running economy, but the EMG activity for the biceps femoris increased 22.6%, stride duration increased 2% and sit and reach range of motion increased 11% whereas drop jump height decreased 9% following static stretch.
These results show that comparatively for an athlete in a 3k race event, the runner may start slowly, with reduced speed and power, but would be able to preserve ultimate event performance in a static stretch versus non stretch condition. In this case, the negative effects of the static stretch were ultimately overcome. The increased hamstring EMG activity and increased stride duration indicates that the athlete may have attempted to increase stride length in an attempt to increase speed to overcome the lower velocity experienced in the first 100 meters of the assessment distance. In this case, the athlete may still be at risk for reduced performance if they were unable to overcome, due to extenuating race circumstances (i.e. being boxed in) the slow start thus questioniong whether if the risk of performance detriment due to pre-race static stretching is worth taking.
What Does This Mean?
This presentation provides a comprehensive review of current available studies as related to static stretching and its effects upon running economy and performance. To date, no systematic reviews or meta-analyses are identified, thus indicating further assessment is warranted. A summary of the above studies provides the following:
- Static stretching and its impact upon running economy and endurance performance has not previously been vigorously studied
- Running economy is a strong predictor of running performance outcome
- Running economy is influenced by many variables, including tissue stiffness
- Tissue stiffness has been shown to improve running economy; less flexible distance runners tend to be more economical
- Static stretching is shown to decrease tissue stiffness
- Static stretching may reduce running economy
- Changes in tissue stiffness, after static stretch, appear to be of limited duration
Without having the support of systematic review and statistical meta-analysis, a definitive statement about the effects of static stretching upon running economy cannot be made. However, several studies support tissue stiffness as a component of running economy and the effect of static stretching upon tissue stiffness and running economy. While further research is clearly warranted, studies suggest that static stretching may impact the following:
- Reduction in local muscle endurance (possibly most influenced by increased set duration vs number of sets and proprioception neuromuscular facilitation techniques).
- Decrease running economy under the following conditions:
- impact may be of limited duration: initial sprint component of race event, 10 minutes, and perhaps up to 20 minutes – depending on duration of stretch
- may not impact lower percentages of aerobic capacity, speed
The findings suggest that the coach and athlete err on the side of caution in regards to static stretching prior to an endurance event. Based on these results and the related findings in the article “Does Stretching Reduce Speed and Power Performance”, this author recommends the following sequence of warmup activities:
- Perform a general aerobic warmup, followed by:
- static stretching (duration of stretch < 45 seconds), when necessary to improve mobility, followed by:
- sport specific dynamic activities, followed by:
- dynamic stretching / activities
Dr Peter J Vilasi MPT DPT is Doctor of Physical Therapy and a USATF Level 2 certified endurance running coach at ExcelRunner