Does Weighted Stretching Build Muscle?
Specifically, we will be examining weighted stretches, one of the more popular variations of extreme stretching. In this article we will discuss the concept of and examine the research on weighted stretches as well as provide suggested exercises for each muscle group that can effectively incorporate weighted stretches.
The goal of weighted stretching is to expand your fascia, which is the connective tissue fibers that attach, stabilize, enclose and separate muscles. Some people believe that expanding your fascia indirectly contributes to larger and fuller muscles. By expanding this connective tissue you create a larger area for your muscles to expand and fill, assuming you provide adequate stimulus through resistance training.
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In the DC community, the recommendation is to perform extreme stretching after each exercise or at the end of the workout. Hold each stretch for 30-60 total seconds and try to flex the target muscle for the entire duration of the stretch. If you cannot compete 30-60 continuous seconds due to duration or intensity, you can split the stretch in to multiple smaller intervals of 5-10 seconds.
Now that we've introduced the concept of weighted stretches, let's delve deeper in to the research to determine if it's an effective muscle builder.
Do not perform any weighted stretch until you've adequately warmed up or worked the target muscle group.
Does Weighted Stretching Actually Increase Muscle Mass?The majority of research on weighted stretches involves hanging weight(s) from the wings of birds. Researchers used a spring-loaded tubular assembly to stretch the wing muscles of four chickens and found that ?Muscles grew in length and cross section in proportion to the extent to which they were stretched?.  Thus, a greater duration and intensity of stretch led to larger increases in muscle mass.
Interestingly enough longitudinal muscle growth topped out after one week but cross sectional muscle growth continued for more than five weeks. Furthermore, the weighted stretches did not decrease nerve activity, immobilize, or increase activity in the muscles but it did increase oxidative enzyme activities.  This means that weighted stretches aren?t necessarily going to cripple or injure you, assuming they?re performed safely and with proper programming.
In a study of seven adult quail, researchers hanged a weight equal to 10% of the quail?s bodyweight to the left wing for 24 hour periods followed by 48-72 hour rest period for a total of 5 days of stretching and a total study duration of 15 days. They found that this protocol increased muscle mass 53.1% (+/- 9.0%) and muscle length 26.1% (+/- 7.3%).
Furthermore, the number of muscle fibers did not change but the number of fast twitch muscle fibers increased by 18.5% (+/- 8.4%).  These Type II fast twitch muscle fibers are crucial for generating force, power, and speed which positively affects weight training efforts.
Another study of 26 adult quail involved hanging a progressively heavier weight, as a percentage of the quail?s bodyweight, from the left wing for 28 days. The protocol was as follows: ?Day 1 (10% wt.), Days 2-3 (rest), Day 4 (15% wt.), Days 5-7 (rest), Day 8 (20% wt.), Days 9-10 (rest), Days 11-14 (25% wt), Days 15-16 (rest), and Days 17-28 (35% wt.)?.
The findings were astounding. After 28 days of this protocol, muscle mass increased by 318%, muscle length increased by 51%, mean muscle fiber area increased by 39%, and fiber number increased by 81%. 
A third study on eight adult quail involved hanging 10% of the quails bodyweight from the left wing for up to 7 consecutive days; researchers found that muscle mass increased most significantly after 48 hours of weighted stretches and after 7 days, the number of muscle fibers increased by 27.1% (+/- 5.8%).  Obviously, these protocols aren?t realistic for a human trainee, but it does suggest that over time, perhaps weighted stretches can help to increase muscle fibers and muscle mass.
Age appears to affect the effectiveness of weighted stretches. When researchers examined 16 12-week old quails and 16 90-week old quails by hanging a weight on the left wing weighing 10% of the quail?s bodyweight for 30 days, they found that both groups increased muscle mass and non-muscle tissue by over 30%, but the 12-week old quails experienced greater increases. 
This is not entirely surprising as we know it's typically easier for trainees in their teens and 20s to build muscle through weightlifting compared to individuals 40+ years of age. Nonetheless, whether you?re a young or old trainee, weighted stretches may help you to build muscle mass, although it won't turn you in to a professional bodybuilder overnight.
With all of this research on birds, you might be skeptical as to whether weighted stretches are effective in human subjects. That's a completely normal response to the research above.
Before we wrap up this section I?ll leave you with one more study on adult animals. Scientists found that in adult animals, on the whole, stretch overload can increase the number of muscle fibers by 9-52% and increase the size of muscle fibers by 10-82%. 
Hopefully this provides slightly more peace-of-mind on the potential merits of using weighted stretches to increase muscle mass. Of course, I encourage you to carefully consider all factors of your training before implementing something like weighted stretches.
Proper weightlifting programming and progression, nutrition, and rest are the cornerstones of gaining muscle mass. With that said, perhaps weighted stretches can provide some added benefits assuming you perform them consistently and properly.
How to Implement Weighted Stretching Into Your RoutineIf you?re looking to implement weighted stretches, the list below provides exercises organized by target muscle group. Do not perform any weighted stretch until you've adequately warmed up or worked the target muscle group.
This typically means performing weighted stretches after performing all exercises targeting that specific muscle group. Alternatively, you can group all weighted stretches at the end of the workout and perform them back-to-back.
Hold all exercises in the bottom/stretched position for 10-30 seconds. Perform 1 to 3 sets and do not go to absolute failure; you should feel an intense stretch but shouldn?t need spotters to assist you in racking the weight.
Target Muscle Group:
- Chest - Dumbbell Fly or Parallel Bar Dip
- Lats - Dumbbell Pullover or (Weighted) Pull-up
- Traps/Upper Back - Dumbbell or Barbell Shrugs
- Biceps - Incline Dumbbell Curl
- Triceps - Overhead Dumbbell or Rope Triceps Extension
- Shoulders - Dumbbell Pendular Swirls*
- Hamstrings - Stiff Legged Deadlift
- Quadriceps - Sissy Squat or Lunge
- Lower Back - 45 Degree Back Extension or Good Morning
- Calves - Standing or Seated Calf Raise
Repeat the exercise but switch directions and swing your arm in circles counter-clockwise. Perform this exercise for both arms, one arm at a time.
Now that we've introduced the concept of, examined research around, and provided suggest exercises for weighted stretches, take this knowledge and apply it. If you decide to incorporate weighted stretches in to your routine, let me know in the comments below!
References1) "Stretch-induced Growth in Chicken Wing Muscles: a New Model of Stretch Hypertrophy. - PubMed - NCBI." National Center for Biotechnology Information. N.p., n.d. Web. 4 Aug. 2015.
2) "Role of Muscle Fiber Hypertrophy and Hyperplasia in Intermittently Stretched Avian Muscle. - PubMed - NCBI." National Center for Biotechnology Information. N.p., n.d. Web. 4 Aug. 2015.
3) "Progressive Stretch Overload of Skeletal Muscle Results in Hypertrophy Before Hyperplasia. - PubMed - NCBI." National Center for Biotechnology Information. N.p., n.d. Web. 4 Aug. 2015.
4) "Muscle Fiber Formation and Fiber Hypertrophy During the Onset of Stretch-overload. - PubMed - NCBI." National Center for Biotechnology Information. N.p., n.d. Web. 4 Aug. 2015.
5) "Hypertrophy and Proliferation of Skeletal Muscle Fibers from Aged Quail. - PubMed - NCBI."National Center for Biotechnology Information. N.p., n.d. Web. 4 Aug. 2015.
6) "Skeletal Muscle Fiber Hyperplasia. - PubMed - NCBI." National Center for Biotechnology Information. N.p., n.d. Web. 4 Aug. 2015.
7) "Shoulder Stretches - Shoulder Flexibility Exercises - PhysioAdvisor." PhysioAdvisor - Physiotherapy, Sports Injuries, Diagnosis, Treatment - Home. N.p., n.d. Web. 4 Aug. 2015.