BJMB

Brazilian Journal of Motor Behavior

Research Article

Villalba et al.

2024

VOL.18

N.1

https://doi.org/10.20338/bjmb.v18i1.405

1 of 12

Muscle activity increased after co-contraction resistance training, but it was unrelated

to the rating of perceived exertion in older adults

MARINA M. VILLALBA

1,2

| RAFAEL A. FUJITA

1,2

| BRUNO L. S. BEDO

| JÚLIA O. FARIA

2,4

| RENATO MORAES

2,4

MATHEUS M. GOMES

1,2

Ribeirão Preto College of Nursing, University of São Paulo, Ribeirão Preto, SP, Brazil

School of Physical Education and Sport of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil

Department of Sport, School of Physical Education and Sport, University of São Paulo, São Paulo, SP, Brazil

Graduate Program in Rehabilitation and Functional Performance, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, SP, Brazil

Correspondence to: Ph.D. Matheus M. Gomes - Assistant Professor

School of Physical Education and Sport of Ribeirão Preto, University of São Paulo

Avenida Bandeirantes, 3900, Ribeirão Preto, Brazil

email: mmgomes@usp.br

https://doi.org/10.20338/bjmb.v18i1.405Do

HIGHLIGHTS

• We investigated the co-contraction training for lower

limbs in older adults.

• There was no correlation between RPE and EMG

activity in co-contraction and conventional resistance

training.

• EMG activity in the co-contraction training was lower

than conventional training.

• EMG activity increased after a period of co-contraction

training.

ABBREVIATIONS

BF Biceps femoris long head

CCT Co-contraction training

CRT Conventional resistance training

EMG Electromyographic

HR Heart rate

MVIC Maximal Voluntary Isometric Contraction

RF Rectus femoris

RMS Root mean square

RPE Rating of Perceived Exertion

ST Semitendinosus

VL Vastus lateralis

VM Vastus medialis

Oxygen consumption

10-CS 10-point cognitive screener

PUBLICATION DATA

Received 21 11 2023

Accepted 12 06 2024

Published 21 07 2024

BACKGROUND: Evaluating exercise intensity is crucial for designing effective training

programs and monitoring progress. The Rating of Perceived Exertion (RPE) scale, a

subjective measure of effort, is commonly used for estimating exercise intensity. However, its

applicability in specific conditions and populations, particularly in co-contraction training and

older individuals, warrants further investigation.

AIM: Our main aim was to analyze the correlation between RPE and electromyographic

(EMG) activity in co-contraction and conventional resistance training. We also compared

muscle activity and RPE across training methods.

METHOD: Twenty-three older adults were allocated and divided into conventional resistance

training (CRT) and co-contraction training (CCT). EMG activity and RPE were recorded for

knee extension and flexion movement and knee co-contraction during training sets and

correlated before and after eight weeks of training.

RESULTS: The results indicated no significant correlation between EMG activity and RPE for

either training method. Additionally, EMG analysis showed higher EMG activity in the CRT

than in the CCT. On the other hand, CCT demonstrated an increase in EMG activity after

eight weeks of training.

CONCLUSION: In conclusion, RPE did not correlate with EMG activity, highlighting the need

for finding accessible tools to assess exercise intensity, particularly in older people, and

alternative training methods, such as co-contraction training.

KEYWORDS: No-load resistance training | Electromyography | Strength | Aging | Borg scale

INTRODUCTION

Accurately assessing exercise intensity is essential for effective training programs

, ensuring safety and monitoring progress

Quantifying exercise intensity is usually based on mechanical, physiological, and psychological aspects, which can be subdivided into

external and internal loads

. External load refers to the parameters that can be recorded during training (heart rate, HR),

electromyographic (EMG) activity, oxygen consumption (VO2), and objective aspects of training (load, volume, sets, repetitions, duration,

intervals, and rests of training)

3,4

. The internal load can be defined as an individual's physiological and psychological response during

exercise and represents the subjective response to an external load (rating of perceived exertion, (RPE))

3,4

. Furthermore, it is worth

highlighting the importance of monitoring internal and external loads, especially for older adults, as the aging process can affect their

BJMB

Brazilian Journal of Motor Behavior

Villalba et al.

2024

VOL.18

N.1

https://doi.org/10.20338/bjmb.v18i1.405

2 of 12

Research Article

ability to generate strength and withstand great efforts, as well as their executive and cognitive function

. Therefore, trainers and

clinicians use different tools to monitor the internal and external loads of training

6,7

. However, among the plenty monitoring methods, RPE

is a widespread and well-known resource, accepted for its convenience, easy application, and low cost

8–10

to measure internal load. RPE,

commonly measured using the Borg scale, gauges effort and discomfort during exercise

. Research consistently validates its accuracy in

estimating physiological effort, especially in aerobic exercise

9,11

Recent evidence supports the validity of the Borg RPE scale in accessing internal load during resistance exercises

. However,

in an exercise environment with multiple influencing factors (e.g., exercise type, practitioner's level of experience, practitioner's

understanding of RPE), RPE's validity can be compromised, challenging its use for intensity monitoring

. Hence, additional studies are

necessary to validate the RPE

for specific strength training methods

, diverse populations (e.g., older adults, non-athletes), and

exercises (e.g., more complex, isolated)

9,13,14

. Although RPE may be an alternative approach to monitoring internal load during strength

training due to its easy implementation, fast application, and avoidance of maximal efforts, it is essential to state that these

recommendations are based on a few studies with older adults

. Furthermore, some studies

10,14

show that RPE assessment has been

used to assess effort throughout an exercise session and is a valid and reliable indicator for monitoring the overall intensity of resistance

training sessions. This involves providing a global rating of the effort level for the entire training session rather than reporting acute RPE

measurements for each exercise within a session. It appears reasonable to assume that performing a single exercise, particularly if it

involves single-joint movements, might engage fewer muscle groups and potentially elicit a lower level of effort, which may not be

accurately perceived by the participant and precisely measured using the Borg RPE scale. Nevertheless, further investigation is required

to substantiate this assumption.

A novel resistance training method, voluntary co-contraction, has been developed and presented sufficient muscle recruitment

to effectively enhance strength

15-17

and muscular hypertrophy

17,18

. This method involves simultaneous voluntary contractions of

antagonist pairs of muscles (e.g., simultaneous contraction of elbow flexors and extensors muscles) without external devices

. Since

voluntary co-contraction demands an organization of excitatory motor commands so that the muscles themselves produce resistive

forces that act against each other

, it is possible that it may pose challenges related to factors such as age, level of experience, and

training

. Moreover, currently, there is no available tool to verify the intensity of co-contraction training other than assessing muscle

activation during the training; unlike conventional resistance training, which can be accessed using methods such as RPE

and

percentage of one-repetition maximum

. To date, no RPE scale has been specifically designed and validated for co-contraction training.

To verify if RPE effectively measures resistance training intensity, it is crucial to investigate its correlation with physiological and

performance parameters

, such as heart rate, total weight lifted, and EMG activity. Some methods of monitoring resistance exercise

intensities through external load require expensive equipment such as dynamometers and surface EMG recording

. EMG is widely

applied in medical, neuroscience, and sports science areas

to assess muscle activity based on the electric potential detected from

muscle fibers' transmembrane current (muscle excitation)

. This allows us to measure the intensity of the exercise based on the values

of muscle activity, although with high equipment cost, time-consuming protocols

, and technical knowledge

. Investigating the

correlation between EMG and RPE could provide a more accessible and cost-effective way to assess intensity, benefiting practitioners

and the public in practical settings.

The EMG activity recorded during contraction is related to the muscle-generated force, which influences the intensity of

physical effort during the task. Therefore, it is reasonable to presume that the intensity of effort affects the perceived exertion.

Furthermore, when interested in measuring localized muscle group effort, it is common to use EMG signals to investigate the level of

muscular excitation during physical activities

. Additionally, different types of strength training can influence both intensity and

perception of effort, considering factors such as exercise selection, rest periods and movement velocity

. How muscles are recruited can

influence both EMG and RPE responses, given that co-contraction involves simultaneous recruitment of agonist and antagonist muscles,

while conventional training often focuses on agonist recruitment. Finally, variations in muscle overload due to different types of exercises

can also influence the responses of both EMG and RPE. Therefore, considering the potential influence of different kinds of exercises on

muscle activity and perception of effort, it becomes interesting to analyze how these variables behave in response to different types of

training. Furthermore, investigating the existence of a relationship between muscle activity measured by EMG and the RPE reported by

participants can provide valuable insights into how these aspects interrelate in different training methods.

Thus, we analyzed the correlation between EMG activity (external load) and RPE (internal load) in co-contraction and

conventional resistance training. Examining the relationship between RPE and EMG allows one to comprehend the most suitable

approach for quantifying exercise intensity in resistance training, particularly co-contraction training. Considering the characteristics of the

training session of our study (exercise programs only for knee muscles composed of few exercises) and the characteristics of our study

population (older adults without previous experience of strength training), we assume that a correlation may not be observed.

Additionally, we compared EMG activity and RPE across training types. Furthermore, isometric exercise substantially elevates blood

pressure and heart rate

. Given limited knowledge of cardiovascular responses to co-contraction training in older individuals, we

prioritized monitoring blood pressure and heart rate for safety.

METHODS