BJMB

Brazilian Journal of Motor Behavior

Research Article

Friderisch et al.

2024

VOL.18

N.1

https://doi.org/10.20338/bjmb.v18i1.427

1 of 11

There is no difference between two and five minutes of static stretching training and

detraining on gastrocnemius medialis muscle thickness, pennation angle and fascicle

length

WILLIAM FRIDERICHS

1,3

| FRANCESCA C. SONDA

| ANELIZE CINI

| GABRIELA FRAPORTI

| MARCO A. VAZ

CLÁUDIA S. LIMA

Biomechanics and Kinesiology Research Group, Exercise Research Laboratory, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

Kinesiology and Kinesiotherapy Research Group, Exercise Research Laboratory, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

Universidade do Vale do Rio dos Sinos, São Leopoldo, RS, Brazil

Correspondence to: Anelize Cini

Exercise Research Laboratory, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

Phone number: +55 54 99967-4342.

email: anelizecini@yahoo.com.br

https://doi.org/10.20338/bjmb.v18i1.427

HIGHLIGHTS

• 6-weeks of passive stretching did not generate muscle

architectural adaptations.

• Ultrasound analyses for muscle thickness have an

excellent inter-analyzer reliability.

• The inter-analyzers reliability for fascicle length is good.

• The inter-analyzers reliability for pennation angle varies

from moderated to good.

ABBREVIATIONS

CI Confidence Interval

CV Coefficient of variance

ES Effect size

FL Fascicle length

GC Control group

GM Gastrocnemius Medialis

G2 2-minutes of PSS

G5 5-minutes of PSS

ICC Intraclass correlation coefficients

IPAQ International physical activity questionnaire

MDC Minimum detectable change

MT Muscle thickness

PA Pennation angle

PSS Passive static stretching

ROM Range of motion

SD Standard deviation

SEM Standard error of measurement

TTUS Total time under stretching

PUBLICATION DATA

Received 01 05 2024

Accepted 26 06 2024

Published 19 07 2024

BACKGROUND: Skeletal muscle’s architecture can undergo temporary or permanent

adaptations when subjected to chronic passive loading, such as during passive static

stretching (PSS).

AIM: We evaluated the effects of a 6-week PSS program, with two and five minutes of

duration, on the architecture of the Gastrocnemius Medialis (GM) muscle. In addition, we

determined the inter-analyzer reliability of the GM’s muscle architecture images analysis

process.

METHOD: 30 healthy adults participated in this study. Participants were divided into three

groups: Control Group (CG), 2-minutes of PSS (G2) and 5-minutes of PSS (G5). Plantar

flexors’ PSS was applied three times a week for 6 weeks. Participants were assessed before

intervention, after intervention, and two weeks post detraining. GM’s muscle thickness (MT),

pennation angle (PA) and fascicle length (FL) were measured with an ultrasound system by

an experienced evaluator. All images were analyzed by two independent analyzers, using the

Image-J software.

RESULTS: No significant effects were identified (p>0.05) of the PSS program on muscle

architecture parameters. No architectural changes were observed following the detraining

period. GM’s MT results presented excellent reliability, while good reliability was found for the

FL measures. For PA, good reliability was only observed for the post-intervention moment. On

the pre-intervention and follow-up moments, the intraclass correlation coefficients values were

moderate.

CONCLUSION: A 6-week PSS program did not generate adaptations on GM’s muscle

architecture parameters in healthy subjects, independent of the stretching duration. Muscle

architecture parameters are reliable when analyzed by different analyzers following clinical

interventions.

KEYWORDS: Ultrasound | Fascicle length | Pennation angle | Muscle thickness | Muscle

Stretching Exercises

INTRODUCTION

Muscle stretching is widely used in rehabilitation programs and sports training with the aim of increasing flexibility and

improving functional performance

1,2

. One of the most popular types of muscle stretching used in clinical practice is the passive static

stretching (PSS). This technique consists in placing the muscles in a maximal position of stretch and holding it there for a determined

time period

It is clear in the literature that, in addition to the fast and easy implementation in training programs, PSS is considered one of

BJMB

Brazilian Journal of Motor Behavior

Friderichs et al.

2024

VOL.18

N.1

https://doi.org/10.20338/bjmb.v18i1.427

2 of 11

Research Article

the safest and most reliable way to obtain range of motion (ROM) gains

4-6

. These flexibility gains are explained based on theories

involving neural and mechanical plastic adaptations

. The neural plastic adaptations are mainly related to an increase in stretch

tolerance, while the mechanical plastic aspects are related to microstructural level responses, such as serial sarcomere number increase

(sarcomerogenesis) and tendon or muscle mechanical properties changes

7-9

Conflicting results have been observed regarding the chronic adaptations of the gastrocnemius medialis muscle (GM’s)

architecture, such as muscle thickness (MT), pennation angle (PA) and fascicle length (FL), after PSS interventions

9-18

. Chronic PSS has

been reported to induce adaptations in GM’s MT (increase or decrease), PA (increase or decrease), and FL (increase)

10-12

, and the total

time under stretching [(TTUS) = (time of each stretching set × number of sets of each session × number of sessions)] in these studies

ranged from 48 to 945 minutes

10-12

. In the studies that did not find changes on GM’s muscle architecture parameters, TTUS ranged from

36 to 672 minutes

9,14-18

. Furthermore, in addition to their differences in TTUS, the studies differed in terms of population, PSS duration

and intensity.

We found three reviews (literature review) about PSS training effects. The first, a systematic review with meta-analysis, did not

identify significant changes on muscle architecture parameters of the biceps femoris and triceps surae muscles after PSS protocols with

durations between 3 and 8 weeks

. The second, concluded that stretching does not appear to confer beneficial changes in muscle size

and architecture

. The third (also a systematic review with meta-analysis), identified that stretching training induces trivial increases in

FL at rest and small increases in FL during stretching, but no increases were observed in either fascicle PA or MT

. However, due to the

heterogeneity of the reviewed studies in relation to the stretching protocols and the different methodologies used, it is not possible to

determine which are the chronic effects of PSS on muscle architecture parameters and how these changes can affect long-term flexibility.

In addition, PSS training effects may be affected by the methodology used for the ultrasound image data collection and data

analysis. B-mode ultrasound is the most popular technique used for measuring the architectonic parameters of skeletal muscles

22,23

Nevertheless, this technique depends of the evaluator’s experience and, therefore, without due training, it can be susceptible to

measurement errors

24,25

. In general, after the image acquisition process, images are exported to a specific image-analyzer software, in

which muscle architecture parameters are measured manually

22,26

. On this step, factors such as different analyzers or analyzers with

different time experience, different evaluation moments and the extrapolation method to quantify the FL may compromise the values of

the analyzed variables

22,27

Studies have reported excellent results for intra-analyzer and inter-analyzer reliability for muscle architecture parameters, with

high values of intraclass correlation coefficients (ICC>0.82)

24,28

. These outcomes are important because they allow to determine if the

method of image analyses, repeated on multiple occasions or by different analyzers, are reliable and sensitive enough to track

adaptations

. Despite that, apparently only two studies investigated if the magnitude of standard error of measurement (SEM) of

ultrasound image analysis surpasses the possible alterations on the variables of interest (MT, PA, and FL), but none of these studies

determined this during and after clinical interventions

24,28

. Furthermore, only one study calculated the minimum detectable change (MDC)

of these parameters

, and, despite being reliable, due to their relatively large MDC, they suggest that clinically derived ultrasound

measurements of muscle architecture in GM are more likely to be useful to detect differences between populations than to detect

changes in muscle architecture following interventions. However, until the present moment, no studies were found in the literature

evaluating all three muscle architecture parameters following interventions and performing a reliability analysis of the architectural

parameters. Therefore, it is not clear how reliable obtained architectural values are, when determining muscular adaptations after clinical

intervention (e.g., chronic stretching), and the assessment of inter-analyzer reliability helps determining strategies to minimize

measurement errors

Therefore, the main objective of this study was to evaluate the effects of a six-week PSS program, with different periods of

execution (two and five minutes) and after two weeks of detraining, on GM’s muscle architecture parameters in healthy subjects. The

detraining was evaluated with the aim of verifying if changes in the musculature that may occur with PSS training are maintained when

the stretching stimulus is ceased, characterizing a probable long-term structural adaptation of the musculature. The second aim of this

study was to determine the inter-analyzer reliability of GM’s muscle architecture image analyses process performed by two analyzers with

different time-experience with the image-analysis methodology during an exercise intervention. Based on the available evidence in the

literature, we hypothesize that muscle architecture parameters will remain unchanged after 6 weeks of PSS training with no changes in

the two weeks of follow-up. Moreover, we expect that well-trained analyzers with different experience-time in ultrasound image-analysis

can obtain excellent reliability results, independent of the intervention time and image analysis experience time.

METHODS

Study design

A randomized clinical trial study was conducted to assess the effects of PSS on muscle architecture parameters. Prior to its

execution, this study was registered in Brazilian Clinical Trials Registry RBR-5j3h3c ((http://www.ensaiosclinicos.gov.br/).

Initially, the participants were randomly divided into three different groups: control group (CG), with no PSS intervention, 2-

minutes group (G2) that performed PSS for two minutes and 5-minutes group (G5), that performed PSS for five minutes. For the

evaluations, the participants visited the laboratory three times. In the first evaluation (pre-stretching), consent was obtained from all

BJMB

Brazilian Journal of Motor Behavior

Friderichs et al.

2024

VOL.18

N.1

https://doi.org/10.20338/bjmb.v18i1.427

3 of 11

Research Article

participants, physical activity was evaluated by the international physical activity questionnaire (IPAQ-short form), and the group and limb

randomizations were performed. The participants’ randomization into the groups was made through an online system

(randomization.com) using the randomly exchanged blocks. Limb randomization was made through drawing between dominant and non-

dominant limb. Next, the assessment of GM’s muscle architecture parameters (MT, PA, and FL) was accomplished with an ultrasound

system by an experienced rater. After six weeks of PSS, on the post-intervention evaluation, the same GM’s muscle architecture

variables were reassessed with a minimum of three days interval from the last PSS session (Figure 1). Two weeks later, the subjects

returned to perform the detraining testing session (follow-up). On all occasions, participants were instructed not to perform any vigorous

physical activity 48 hours before the tests

Figure 1. Study design timeline.

Participants

The G∗Power software (Kiel University, Germany) was used to calculate the sample size. A repeated measures ANOVA was

used, with within-between interactions (F-test family) and, with a priori power analysis, were used to calculate the sample size with α =

0.05, power = 0.80, and effect size f = 0.18. This calculation was performed using values from GM’s PA effect size (ES) value (ES: 0.36)

from a previous study

. A 95% Confidence Interval (CI) and a maximum admitted error of 5% were used. The sample size calculation

totaled 30 subjects. To accommodate possible dropouts, 33 subjects were recruited among recreationally active university students.

Participants aged between 18 and 40 years, who were physically active but not engaged in strength and flexibility training

based on the IPAQ short form, were included. The exclusion criteria were: (1) having any previous history of musculoskeletal injuries or

surgery on the lower limbs; (2) presenting continuous pain on the lower limbs; (3) using analgesics, anti-inflammatory, or muscle

relaxants; (4) presenting hypermobility syndrome, according to the Beighton Score; and (5) having any metabolic diseases, such as

diabetes mellitus.

All participants signed an informed consent form containing all the information pertinent to this study, approved by the

University’s Ethics Committee for Human Research (project number: 2.139.313) according to the Declaration of Helsinki.

Procedures

Static Stretching Intervention

PSS training for the plantar flexor muscles was applied with a frequency of three times per week, during six weeks, using a step

with at least 15 cm of height. Participants stood erect, with the lower limb being stretched with the forefoot supported on the step, and

both arms against a wall in front of the body to provide balance (Figure 2). They were instructed to stretch the ankle with the highest

intensity tolerated as possible, until reaching the greatest ankle dorsiflexion angle. The stretching protocol was made in the laboratory

with researcher’s supervision. G2 remained in this stretching position for 2 minutes while G5 remained for 5 minutes. Although only one

lower limb was evaluated, both limbs were stretched during intervention, one at a time.

Measurements of Gastrocnemius Medialis Muscle Architecture

An ultrasound system (SSD-4000; Aloka Inc., Tokyo, Japan) with a 60mm linear array probe (7.5 MHz) was used to determine

GM’s MT, PA, and FL. Three ultrasound images were obtained at each time point (i.e., before, after, and two weeks post-intervention) by

an experienced evaluator (3 years of experience with the technique) that was blinded to the participants group and time-point of

intervention. During image acquisition, the subjects remained lying down on a stretcher in a prone position, with the feet positioned out of

the stretcher and the ankle joint at 0° (neutral position). The ankle joint position was maintained with the aid of a goniometer. The

ultrasound probe was positioned longitudinally to the muscle fibers and perpendicular to the skin at 30% of the distance between the

popliteal crease and the lateral malleolus

. A layer of water-soluble transmission gel was used to provide acoustic contact between the

skin and the probe.

For the muscle architecture analysis, MT was considered the distance between the deep and the superficial aponeuroses and

was calculated through the mean value of five parallel lines drawn between these reference points along each ultrasonography image