Acute Effects of Stretching Before Workouts and Long-Term Effects of Separate Stretches | Plus: Stretch→Hypertrophy?

I am not aware of studies on intra-workout stretching as joggers do it sometimes.

I've recently overheard a discussion about stretching between the two other members of my gym. Both of them were highlighting out how detrimental stretching before workouts was and that, instead, you should do your stretches at the end of your workouts because, after all, you don't wont to lose your flexibility. Oh my, if things only were that simple...

Even if we just refer to the few studies on stretching that were published in 2018, it becomes evident that one-size-fits-it-all solutions like "stretch after, never before workouts" are problematic and may even do more harm than good.

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In this article, I want to briefly address two of the most prevalent misconceptions about stretching, which are also related to the quintessence of the previously described conversation:

1. There are just two ways to stretch, dynamically and statically and static stretches must never be done before exercise because they'll decrease your performance, and...
2. unlike increases in flexibility the performance effects of static stretching are acute and transient (yesterday's stretch won't affect today's workout).

Two recent studies on the short-term effect of static stretching with different durations and the long-term effects of a standardized stretching regimen show that (1) the effects of static stretching crucially depend on the duration of the stretch, and that (2) the assumption that the performance effects of stretching were transient and any effects observed in the long-term were just the result of improvements in flexibility is questionable if not totally flawed.

• Short-term effects depend on the duration of the stretch: In their latest study, Alizadeh Ebadi & Cetin (2018) tried to determine the optimal stretching duration in fifteen elite male athletes from two different sport-branches (10 footballers and 5 basketballers). The study involved a complex static stretching program for quadriceps, hamstrings, calves, adductors, and hip rotators. In all four study groups, the subjects warmed up with a 5-minute jog but Group A did no stretching at all, Group B did every stretch for 15 s,  Group C performed every stretch for 30 s, and Group D did each stretch for 45 s.
  

  

  Figure 1: Difference in isokinetic strength measurements compared to the control condition (jogging alone) for fast (180°/s) and slow contractions (60°/s | Alizadeh Ebadi & Cetin 2018) 

  In the subsequent strength test, the implementation of stretching, the angular velocity (the speed at which the leg was moved) and the duration of the stretches had interacting effects on the isokinetic strength measurements the scientists obtained by the means of an Isomed 2000 device. It is thus difficult, if not impossible to formulate universal recommendations. What seems to be clear, though is that...
  • if exercises are executed fast/explosively there's a high risk that the strength will be impaired by pre-exercise static stretching,
  • the longer the static stretch is maintained the smaller are the potential benefits and the larger are the risk and extent of detrimental effects due to static stretching, and ...
  • stretching for only 15 seconds won't impair isokinetic strength on exercises that require rapid muscle contractions and may even improve isokinetic strength on exercises that are performed at a slower pace.
  In view of the fact that the study at hand measured only the subjects' isokinetic strength and didn't assess the effects of static stretching on actual athletic performance (e.g. sprints as you'd need them in both football and basketball), further studies are warranted to identify potential exercise specific (both in terms of target muscles and execution speed) effects of static stretching of different durations on athletic performance.
  
  What appears to be certain even now, though, is that there's no one-size-fits-it-all approach to static stretching and that there may be sports (with slow muscle contractions) in which a brief static stretch before training or competing could even improve an athlete's subsequent isometric strength and the related physical performance.

In Goldspink et al. the EDL muscle protein synthesis exploded when it was stretched and forced to contract for 3 days.

Doesn't stretching also promote hypertrophy? I know it takes time that you'd rather use to do yet another set of bench presses or another type of biceps curls but in view of the fact that stretching alone has been found to induce sometimes highly significant increases in skeletal muscle protein-synthesis and long(er)-term hypertrophy in animal studies (see Figure on the left; cf. Alway 1985; Goldspink 1995; Day 1997; Yang 1997), the 5-10 minutes you would have to invest to get a decent stretching protocol done could be a smart investment into extra muscle gains that may pay off over weeks and months of training.

However, even if the results of the previously referenced animal studies translate 1:1 to human beings, this does not mean that stretching separately will add to the hypertrophy stimulus of resistance training - meaning, if you do it after lifting heavy weights, stretching may not provide additional because mTOR & co (Zanchi 2008) may already be maxed out. If you do both at the same time, however, the Goldspink study, which combined electrical muscle stimulation (EMS, 20 Hz for 3 days) and stretching (with the feet fixed in a position that would chronically stretch the extensor digitorum longus (EDL) muscle), there may be synergistic effects that increase the protein synthesis by >300%, (see Figure), the 3-day muscle growth by 35% and the IGF-1 response 40-fold... unrealistic? True, if we're talking about integrating 24h stretch + EMS into your everyday lives. However, some of you may be reminded of the old-school bodybuilding advice to "do stretching exercises towards like dumbbell flies towards the end of your workouts and perform partial reps in the stretched position" - I can't tell, if that actually helps, because human studies that combine stretch and contraction don't exist.

Muscle thickness in Simpson 2017 for the stretched and nonstretched legs for the six-week intervention and 1 week post-training. *, an increase in muscle thickness for all time periods compared with baseline for the stretched leg. †, significant difference between the stretched and nonstretched legs.

What I can tell you, though is that studies from the 1990s report increases in strength performance in response to separate stretching of which the authors believe that they have been facilitated at least partly by skeletal muscle hypertrophy (Worel 1994; Handel 1997). Moreover, Simpson et al. (2017) have demonstrated only recently that stretching the gastrocnemius five times per week for six weeks (a singlethree minute stretch on the 45° leg press with progressively increased load) "is a viable modality to alter muscle architecture of the human gastrocnemius through lengthening of muscle fascicles, decreasing pennation angles, and increasing muscle thickness" (my emphasis in Simpson 2017 | see Figure on the right) when protein is provided right after the stretch stimulus (here 0.25g/kg whey isolate).

• In the long-term flexibility & rate of force development increase, but strength endurance decreases: Similar negative effects have recently been observed by Ikeda & Ryushi (2018), who conducted a study that provides important insights into the longitudinal effects of stretching on muscle strength and endurance.
  
  

  

  Figure 2: This is the stretch the subjects in the Ikeda & Ryushi study performed for 6 sets of 30 s 3x per week over the course of a 6-week study (Ikeda & Ryushi 2018).

  The scientists from Japan compared the effects of a standardized 6-week stretching protocol (3x per week) on the athletic performance of previously non-(resistance-)trained subjects. The protocol was designed in line with the ACSM guidelines but was restricted to the flexion of the knee joint in the lateral decubitus position, with the participant holding the ipsilateral foot with his hand (see Figure 2). All six sets of 30s-stretches were supposed to be performed up to the point where the stretch began to became painful.
  
  As you can see in my plot of the data, there was a significant effect of stretching on both flexibility and the rate of force development of the quads.
  

  

  Figure 3: Relative changes in max. strength, rate of force development, and strength endurance in response to 6 weeks w/ 3x stretching days à 6 sets of 30s seconds quad stretches (Ikeda & Ryushi 2018)

  On the other hand, the subjects' strength endurance, which was assessed during a 50-rep leg-extension exercise in form of the strength decrement index which quantifies the strength changes in workload over time, declined - interestingly enough, though, only in the early, but not in the late phase of the test when the untrained subjects were probably so fatigued that any long-term effects of static stretching on muscular activation patterns were overridden by local and/or systemic fatigue.

You may not remember it, but stretching has been found to ameliorate the postprandial glucose search, only recently => "Surprise: Within the statistical margin of error stretching and resistance training are equally effective in reducing the post-prandial glucose surge in type II diabetics" | read more.

So what's new in stretching science? In conjunction, the two studies I chose show that (a) doing static stretches before your workouts is not necessarily bad for you and that (b) stretching after your workouts will, in the long(er) term, i.e. over weeks and months, affect more than just your flexibility.

The acute effects - and that's probably the most important contribution of Alizadeh Ebadi's and Cetin's study - critically depend on the duration of the stretch, with a short 15-second stretch having no or a small beneficial effect, and stretching for 30-45 seconds having negative or neutral effects on your isokinetic strength during exercises that involve fast and slow muscle contractions, respectively.

This result is corroborated by another 2018 study by Iatridou et al. (2018) who didn't modify the duration of the individual stretches, but the number of sets. They found a significant decrease in sprint performance in teen soccer players when the subjects did two or three sets of 20s-stretches. If they did only one set, however, the subjects' performance was not impaired and the increase in flexibility was identical to the 2x and 3x-20s trials.

To find corroborative or conflicting evidence for Ikeda's and Ryushi's "long"-term (6-week) study is much more difficult, as most of the research are studies that assess the acute response to a given stretching regimen. The differential effects on athletes' long-term performance, on the other hand, are often neglected in studies that focus mainly or exclusively on increases in flexibility. That's a pity, because the increases in flexibility can be accompanied by other, for many sports more important changes in parameters such as maximal force, the rate of force development and the subjects' strength endurance - changes of which the Ikeda & Ryushi study suggests that they would be beneficial for long-jumpers or shot putters (increased explosive strength and force production), but detrimental to Crossfit athletes, whose performance would suffer significantly from the decrease in strength endurance the Japanese researchers observed | Comment!

References:

• Alizadeh Ebadi, Leyla, and Çetin, Ebru. "Duration Dependent Effect of Static Stretching on Quadriceps and Hamstring Muscle Force." Sports 6.1 (2018): 24.
• Alway, Stephen E. "Force and contractile characteristics after stretch overload in quail anterior latissimus dorsi muscle." Journal of Applied Physiology 77.1 (1994): 135-141.
• Blazevich, Anthony J., et al. "No effect of muscle stretching within a full, dynamic warm-up on athletic performance." Medicine & Science in Sports & Exercise 50.6 (2018): 1258-1266.
• Day, Charles S., et al. "Limb lengthening promotes muscle growth." Journal of orthopaedic research 15.2 (1997): 227-234.
• Handel, M., et al. "Effects of contract-relax stretching training on muscle performance in athletes." European journal of applied physiology and occupational physiology 76.5 (1997): 400-408.
• Iatridou, Georgia, et al. "Acute effects of stretching duration on sprint performance of adolescent football players." Muscles, Ligaments & Tendons Journal (MLTJ) 8.1 (2018).
• Ikeda, N and Ryushi, T. "Effects of 6-week static stretching of knee extensors on flexibility, muscle strength, jump performance, and muscle endurance." J Strength Cond Res (2018): ahead of print.
• Kokkonen, Joke, et al. "Chronic static stretching improves exercise performance." Medicine & Science in Sports & Exercise 39.10 (2007): 1825-1831.
• Lima, Camila D., et al. "Effects of Static Versus Ballistic Stretching on Hamstring: Quadriceps Strength Ratio and Jump Performance in Ballet Dancers and Resistance Trained Women." Journal of Dance Medicine & Science 22.3 (2018): 160-167.
• Reid, Jonathan C., et al. "The effects of different durations of static stretching within a comprehensive warm-up on voluntary and evoked contractile properties." European journal of applied physiology (2018): 1-19.
• Rubini, Ercole C., André LL Costa, and Paulo SC Gomes. "The effects of stretching on strength performance." Sports medicine 37.3 (2007): 213-224.
• Simpson, C. L., et al. "Stretch training induces unequal adaptation in muscle fascicles and thickness in medial and lateral gastrocnemii." Scandinavian journal of medicine & science in sports 27.12 (2017): 1597-1604.
• Shrier, Ian. "Does stretching improve performance?: a systematic and critical review of the literature." Clinical journal of sport medicine 14.5 (2004): 267-273.
• Worel et al. "Effect of hamstring stretching on hamstring muscle performance." J Orthop Sports Phys Her 20.3 (1994): 1549. 
• Yang, Shiyu, et al. "Changes in muscle fibre type, muscle mass and IGF-I gene expression in rabbit skeletal muscle subjected to stretch." The Journal of Anatomy 190.4 (1997): 613-622.
• Zanchi, Nelo Eidy, and Antonio Herbert Lancha. "Mechanical stimuli of skeletal muscle: implications on mTOR/p70s6k and protein synthesis." European journal of applied physiology 102.3 (2008): 253-263.