What Exactly Is The Impact of Stretching On Muscle Size And Strength?

Stretching is a part of physical activity and is considered more important in some sports compared to others. In those that resistance train, the emphasis put on stretching ranges considerably. It’s evident from research that stretching enhances joint range of motion⁽¹⁾.

Recent research indicates stretching performed for several weeks has the potential to induce increases in maximal strength and hypertrophy^(2,3)
 
Recently, static stretching has been indicated as a potential alternative to common resistance-training methods, as research showed no significant difference in strength, muscle growth and flexibility when comparing 1 hour of daily stretching with a commonly performed muscle growth training routine (5 × 12 repetitions, three times per week⁽⁴⁾.  

As resistance training also enhanced range of motion similarly to static stretching, the practical application and additional benefit of adding stretching to a trained muscle group needs to be considered critically.

In addition, there is very little evidence in upper body muscles as most strength training research is limited to lower extremity muscles.

As mentioned, very little research has been done on upper body (i.e. pectoralis muscles) maximal strength and stretching. In addition, there is no data supporting morphological adaptations (i.e. muscle growth) contributing to maximal strength increases that occurs from a stretching program.

A recent study investigated if static stretching on the pectoral muscle performed 15 min, 4 days per week can enhance maximal strength, muscle thickness and flexibility⁽⁵⁾.

To check the practical relevance, the effects were compared with a commonly performed resistance training routine.

• - Eighty-one active participants were allocated to either a static stretching, strength-training, or control group.
• - The pectoralis stretching group performed supervised, continuous 15-min static stretching training 4 days per week over 8 weeks on a stretching board.
• - To contrast high-volume stretch training to commonly performed resistance training, participants of the strength-training group performed standardized resistance training of the chest muscles 3 days per week for 8 weeks.
• - They utilized the butterfly machine exercise to target the pectoralis major and performed 5 sets of 10–12 repetitions using the 10–12RM with 90 second interset rest). Progressive resistance was utilized over the course of the program.

Major Findings

This study compared the effects of 8 weeks of supervised static stretching with resistance training on strength capacity, muscle thickness and flexibility in the pectoralis muscle. Static stretching and resistance training showed comparable results with significant increases in maximal strength and muscle thickness.

These results agree with current evidence in human studies demonstrating that high-volume stretching can increase strength and muscle size.

Until now, there were no studies that directly compared stretch and resistance training on muscle strength and hypertrophy in human pectoralis muscle. This is the first investigation that measured muscle size in the upper extremities comparing stretching and resistance training.

Mechanism of Action

There seems to be a shared underling physiological mechanism between stretching and resistance training. Muscle hypertrophy could be explained by translating mechanical tension into chemical signals that stimulate anabolic processes such as satellite cell activation to generate new muscle tissue.

Prior research described stretching intensity to be of crucial importance to induce structural muscle changes, hypothesizing stretched-mediated inflammatory processes. A sufficient stimulus from high degree stretching intensity can unfold titin filaments which can be hypothesized to be involved in the muscle hypertrophic response⁽⁶⁾.

Figure: Overview of the mechanisms known to modulate titin-based force in the skeletal muscle sarcomere⁽⁶⁾.

Some of these mechanisms were frequently suggested to be involved in muscle hypertrophy after resistance training as well.

Assuming mechanical tension to be of crucial importance, stretching intensity could be hypothesized to impact morphological adaptations. Apart from mechanical tension and morphological parameters, neural adaptations cannot be ruled out to be responsible for strength increases.

Practical Applications

Although there seems to be positive effects from stretching, the practical applications are limited. Regular resistance training provides additional health benefits, such as prevention of sarcopenia and osteoporosis and enhances cardiovascular health. The effects of stretching on bone density and sarcopenia were not explored in previous research.  

It also seems the practical application of using stretching to enhance muscle strength and cross-sectional area is limited because resistance training is assumed to be more time efficient.

There are situations where stretching serves as a potential alternative such as when a person isn’t willing to invest in the effort in exercise sessions in the gym, stretching might be applicable as a home-based training program.

There may be situations when the possibility to perform resistance training is limited, and in situations such as post-surgery rehabilitation. One of the major limitations of this study was that the participants of this study were recreationally active and not resistance trained.

Summary

These results further the emerging evidence that stretching can have potent effects on muscle development. This study was intriguing because mechanistically it indicates that passive tension can have potent hypertrophic effects.

This has application to exercises, including training at long muscle lengths and employing static stretch holds (e.g., at end of sets). 

To really understand the value of stretching in a trained population, future research should compare a resistance-training only group to a combined resistance training and stretch group using trained individuals.

You can learn more about how eccentric training enhances muscle size here.


References:
    1.    Konrad A, Alizadeh S, Daneshjoo A, et al: Chronic effects of stretching on range of motion with consideration of potential moderating variables: A systematic review with meta-analysis. J Sport Health Sci, 2023
    2.    Arntz F, Markov A, Behm DG, et al: Chronic Effects of Static Stretching Exercises on Muscle Strength and Power in Healthy Individuals Across the Lifespan: A Systematic Review with Multi-level Meta-analysis. Sports Med 53:723-745, 2023
    3.    Panidi I, Donti O, Konrad A, et al: Muscle Architecture Adaptations to Static Stretching Training: A Systematic Review with Meta-Analysis. Sports Med Open 9:47, 2023
    4.    Warneke K, Hillebrecht M, Claassen-Helmers E, et al: Effects of a Home-Based Stretching Program on Bench Press Maximum Strength and Shoulder Flexibility. J Sports Sci Med 22:597-604, 2023
    5.    Wohlann T, Warneke K, Kalder V, et al: Influence of 8-weeks of supervised static stretching or resistance training of pectoral major muscles on maximal strength, muscle thickness and range of motion. Eur J Appl Physiol, 2024
    6.    Freundt JK, Linke WA: Titin as a force-generating muscle protein under regulatory control. J Appl Physiol (1985) 126:1474-1482, 2019