Muscle endurance measurement using a progressive workload and a constant workload by maximal voluntary contraction

doi:10.4236/health.2010.211186

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Vol.2, No.11, 1255-1259 (2010)

doi:10.4236/health.2010.211186

Health

Openly accessible at

Muscle endurance measurement using a progressive

workload and a constant workload by maximal

voluntary contraction

Shinichi Demura1, Masakatsu Nakada2*

1Graduate School of Natural Science & Technology, Kanazawa University, Kanazawa, Japan;

2National Defense Academy, Yokosuka, Japan; *Corresponding Author: [email protected].

Received 12 August 2010; revised 18 August 2010; accepted 25 August 2010.

ABSTRACT

Muscle endurance measurement using a pro-

gressive workload method may reduce pain

sensation in the subject. This study aimed to

examine the relationships between force-time

parameters during sustained static gripping as

measured by maximal voluntary contraction

(MVC) using either a progressive workload (PW)

or a constant workload (CW). Sixteen subjects

performed sustained static gripping with 7 gra-

dually increasing relative demand values of 20%

to 80% MVC and sustained static gripping by

MVC. The staging of progressive workload was

10 s for 20% MVC, 20 s each for 30, 40, 50, 60,

and 70% MVC, and 10 s for 80% MVC. The forces

exerted at 120 s in the CW and PW methods

were at around the 23-27% MVC level. Peak

force, final force, and force during the last 30 s

for the PW method evaluated muscle endurance

after 1 min and showed high correlations (r =

0.746 − 0.895). Significant correlations (r = 0.575

− 0.605) were found between time to 40% MVC in

the CW method and peak force, final force, and

force in the last 30 s in the PW method group.

The peak force in the PW method may be useful

for evaluating muscle endurance with a short

testing time and without high pain sensation.

Keywords: Sustained Static Gripping; Progressive

Workload; Constant Workload; Muscle Endurance

1. INTRODUCTION

Muscle endurance has been measured by maximal vo-

luntary contraction (MVC) or fixed relative load intensity

[1-6]. Many researchers have reported force-decrease

properties exerted in the constant workload (CW) me-

thod [6-8]. Yamaji et al. [8] examined the physiological

properties of force-time parameters during maximal sus-

tained static gripping and reported that time to 40%

MVC reflects the individual difference of force based on

oxygen debt with muscle blood flow limitation. Muscle

endurance measurement using the force exertion by

MVC may be effective, but there are problems with se-

vere muscle-fatigue or dislike of the testing procedure.

In the case of evaluating muscle endurance from the

perspective of sustaining demand values, according to

Nagasawa et al. [6], the sustained time is very short

(about 16 ± 13 sec) when using the heavy workload

(75% MVC) and is very long (about 224 ± 144 sec) when

using the light workload (25% MVC). Even when using

any workload, the force value reaches a steady state at

15%-20% MVC and then decreases little [6,8,9].

Meanwhile, the progressive workload (PW) method

gradually increases the relative loads while considering

the physiological responses [10,11]. Measuring muscle

endurance by this method can reduce the physical bur-

den on the subjects (dislike, pain sensation, etc), because

this method does not impose rapidly large workloads on

the muscle groups. The PW method is also considered to

be effective for the elderly, with whom there is increased

risk associated with a rapid increase of blood pressure.

When considering the physiological parameters of mu-

scle endurance measurements based on MVC, it is im-

portant to remember that during the initial force exertion

due to large workloads, muscle endurance is evaluated in

a state of blood flow obstruction caused by an increase

in intramuscular pressure. On the other hand, the low

force exertion state in the latter half of the measurement

period evaluates muscle endurance in a state of sufficient

oxygen delivery to the muscles, with the resumption of

blood flow caused by the reduction of intramuscular

pressure [8,12]. The PW method may be able to evaluate

muscle endurance without significant fatigue or dislike

S. Demura et al. / HEALTH 2 (2010) 1255-1259

1256

Openly accessible at

and with higher safety. However, the relationships be-

tween evaluation parameters of muscle endurance for the

PW method and for the constant workload (CW) method

are unclear. It is assumed that the parameters in above

both methods have close relationships, because they are

measuring the same grip muscle endurance.

This study aimed to examine the relationships be-

tween force-time parameters during sustained static grip-

ping using both a progressive workload and a constant

workload by maximal voluntary contraction.

2. METHODS

2.1. Subjects

Subjects were 16 young male adults (height 172.7 ±

5.2 cm, body weight 67.1 ± 6.1 kg, and age 21.6 ± 2.0

years). Written informed consent was obtained from all

subjects after a full explanation of the experimental pur-

pose and protocol.

2.2. Materials

Grip strength was measured using a digital hand dy-

namometer with a load-cell sensor (EG-100, Sakai, Ja-

pan). Each signal was sampled at 20 Hz through an ana-

log-to-digital interface and then relayed to a personal

computer. The changes of force values on the computer

display were shown on a time-series graph on the hori-

zontal scale, and relative values were shown on the ver-

tical scale. The display of the target force line was fed

back to the subjects.

2.3. Setting of Progressive and Constant

Workloads

When using loads over 75% maximum voluntary con-

traction (MVC), subject can sustain a target force [6,13].

In addition, the force exertion value in loads of less than

20% of MVC decreases little [6]. Hence, this study se-

lected a measurement time of 2 min with progressive

workloads of 20%-80% MVC. Yamaji et al. [14] re-

ported that the gripping force during maximal sustained

hand grip remarkably decreased until about 30-60 s and

reached an almost steady state when it decreased to 20%

MVC (within about 150 s). Hence, a constant workload

of 100% MVC and a measurement time of 3 min were

selected.

2.4. Experimental Procedure

After measuring maximal grip force, each subject per-

formed the sustained static gripping using the dominant

hand with a progressive workload having 7 relative de-

mand values (20% to 80% MVC) increasing by 10%

MVC each. The subject’s dominant hand was determined

based on Oldfield’s handedness inventory [15]. The time

of the demand values was 10 sec for 20% MVC, 20 sec

each for 30, 40, 50, 60, and 70% MVC, and 10 sec for

80% MVC. The sustained static maximal griping time

was 3 min for 100% MVC. Considering the fatigue ef-

fect, each measurement was performed once a day.

2.5. Parameters

Referring to previous studies [8,9] using sustained sta-

tic maximal hand gripping, the following progressive

workload (PW) parameters were selected: 1) peak of

force value (peak force), 2) time of peak force (peak

force time), 3) final force value (final force), and 4) av-

erage force during the last 30 s (last 30 s force). The fi-

nal force value was the force exerted at 120 s (Figure 1).

The following constant workload (CW) parameters by

maximal voluntary contraction were selected: the time

required to decrease from maximal grip strength to 1)

30% MVC, 2) 40% MVC, 3) 60% MVC, and 4) 80%

MVC; 5) 120 s force; and 6) final force value (final for-

ce) (Figure 2).

2.6. Data Analysis

Pearson’s correlation coefficient was used to examine

the relationships between CW parameters and PW pa-

rameters. A probability level of 0.05 was used as indica-

tive of statistical significance.

3. RESULTS

Figures 3 and 4 show average curves of changes in

time-series forces during sustained static gripping by

MVC using either PW or CW. The peak force appeared

at 60% MVC. The force then decreased until the end of

the 2 min measurement, and the final force was about

27% MVC. The individual difference of force exertion

0 20406080100120

Demand value

Exerted force

Peak force

Peak force timeFinal force

sec

%MVC

Last 30s

force

Figure 1. Progressive workload parameter.

S. Demura et al. / HEALTH 2 (2010) 1255-1259

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Openly accessible at

100

0306090120 150 180

Force

Time to 80% MVC

Time to 60% MVC

Time to 40%MVC

sec

%MVC

Final force

120 s force

Time to 30%MVC

Figure 2. Constant workload parameter.

020 40 60 80100120

Demand value

Exerted force

sec

%MVC

Figure 3. Average curves of changes in time-series forces dur-

ing sustained static gripping by MVC using either PW.

100

0 3060901201501

Force

sec

%MVC

Figure 4. Average curves of changes in time-series forces dur-

ing sustained static gripping by MVC using either CW.

values increased from 60 s (demand value: 50% MVC)

to 90 s (demand value: 70% MVC) after the onset of

sustained static gripping. The force values during sus-

tained static gripping using MVC decreased markedly

until 60 s after sustained static grip onset and reached

nearly 40% MVC. The individual difference of force

values increased until 30 s after the onset of gripping and

then reduced until 60 s at which point a steady state was

reached.

Table 1 shows the correlations between PW and CW

parameters. Significant and high correlations (r = 0.713-

0.895) were found among PW parameters. In CW pa-

rameters, significant and high correlations (r = 0.709-

0.868) were found between time to 80% MVC and time

to 60% MVC, between time to 60% MVC and time to

40% MVC, and between times to 30%-40% MVC and

120 s force. Time to 40% MVC in the CW method showed

significant correlations with peak force, final force, and

last 30 s force in the PW method.

Mean of peak force time in the PW method was about

83 s, and mean decreased times until 80%, 60%, 40%

and 30% MVC in CW method were about 14 s, 31 s, 60

s, and 89 s, respectively. Final force and last 30 s force

in the PW method were about 27% MVC and 35% MVC,

respectively. The 120 s force and final force in the CW

method were 20 and 23% MVC, respectively.

4. DISCUSSION

High correlations (0.713-0.895) in this study were found

among peak force, peak force time, final force, and last

30 s force. The peak force is an unsustainable progres-

sive workload time point, and peak force time was 83.4 s.

Because these parameters evaluate muscle endurance

after 1 min (80-120 s), they are considered to have high

correlations among their parameters.

Meanwhile, parameters in the CW method showed

high correlations (r > 0.70) only between respective near-

ness decreased times as follows: time to 80% MVC and

time to 60% MVC, time to 60% MVC and time to 40%

MVC, and time to 40% MVC and time to 30% MVC.

Since the decrease to 40% MVC takes about 1 min, sub-

jects feel significant pain for a long period of time.

Meanwhile, the mean time of the peak force in the PW

method, which gradually increases loads, was about 83 s

without large pain sensation. This time is nearly equiva-

lent to the time to 30% MVC (88.8 s) in the CW method,

but the force (63.9% MVC) was around twice that

measured at 30% MVC. The forces exerted at 120 s in

the CW and PW methods were at the 20% MVC level

(PW: about 27% MVC, CW: 23% MVC). Hence, the

PW method may be able to exert twice the force of the

CW method at about 90 s without large pain sensation.

However, the force after the peak force decreases re-

markably similarly to the initial phase in the CW method,

and the force after 120 s is considered to decrease to a

nearly comparable level. Yamaji et al. [9] reported that

the gripping force that a person can sustain without de-

crease was 15% MVC (about 150 s) of maximal grip.

Hence, the exertion force in the PW method also reaches

an almost steady state after 120 s.

Peak force in the PW method correlated significantly

with time to 40% MVC in the CW method (r = 0.605).

The time to 40% MVC corresponds to the phase which

S. Demura et al. / HEALTH 2 (2010) 1255-1259

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Table 1. Correlations between PW parameters and CW parameters.

Parameter Unit Mean SD CV

Peak

force

Peak

force

time

Final

Force

Last

30s

Force

Time to

80%

Time to

60% Time to

40% Time to

30%

120s

force

Peak force % MVC 63.9 4.8 7.5

Peak force

time sec 83.4 10.1 12.1 0.775*

Final Force % MVC 27.4 6.5 23.6 0.746*0.713*

Progressive

Workload

Last 30s Force % MVC 34.7 9.7 28.0 0.895*0.878*0.874*

Time to

80%MVC sec 14.3 7.7 54.0 -0.122-0.071-0.0600.005

Time to

60%MVC sec 30.8 9.9 32.2 0.3360.2060.3980.4160.712*

Time to

40%MVC sec 60.4 17.4 28.9 0.605*0.4290.575*0.594*0.4250.738 *

Time to

30%MVC sec 88.8 24.8 27.9 0.3090.1910.3260.3080.4730.581 * 0.868 *

120s force % MVC 22.7 4.8 21.3 0.2180.2110.1250.2690.536*0.463 0.709 * 0.845*

Constant

Workload

Final Force % MVC 20.0 8.5 42.4 0.1780.3980.2950.3350.3210.149 0.346 0.2670.396

Note: *(p < 0.05)

uses more oxygen due to blood flow reflux and which

shows a gender difference in muscle endurance [16]. In

short, this time is considered to evaluate the moving

phase from a state of blood flow obstruction to a state of

blood flow reflux. Peak force in the PW method is con-

sidered to closely relate with the above phase during

maximal sustained gripping. From significant correla-

tions (r = 0.575-0.594) found between the time to 40%

MVC in the CW method and the final force and last 30 s

force in the PW method, the phase after reaching peak

force may produce a similar phenomenon to the moving

phase in the CW method.

Openly accessible at

Meanwhile, at a submaximal constant workload (ex.

50% MVC), the pain sensation may be reduced. How-

ever, according to Nagasawa et al. [6], the sustained

time becomes very long when using a light workload

(50% MVC) which increases the sense of fatigue.

Therefore, even a submaximal constant workload method

cannot solve the problem.

Royce [17] compared force-decrease curves during

sustained static maximal gripping with and without oc-

clusion of arterial blood flow, reporting that they were

similar in the phase of over 60% MVC. That is, it is

considered that the phase over 60% MVC in sustained

static maximal gripping produces a blood flow obstruc-

tion and that the recruitment and fatigue of fast twitch

fibers is largely reflected. Parameters evaluating the

blood flow obstruction phase of sustained static maximal

gripping in this study are time to 80% MVC and time to

60% MVC. They may estimate an individual difference

of muscle endurance in blood flow obstruction phase.

Significant correlations were not found between the above

initial parameters (time to 80%, time to 60% MVC) and

4 PW parameters. The PW parameters may not be able

to evaluate the blood flow obstruction state.

However, in the case of the CW method by MVC,

both phases of blood flow obstruction and blood flow

reflux appear. Hence, Yamaji et al. [9] suggested that the

CW method can evaluate muscle endurance in these two

phases. In the future, the examination of the muscle

oxygenation kinetics during force exertion by the PW

method will be needed to clarify relationships with phy-

siological parameters.

5. SUMMARY

In summary, peak force, final force, and last 30 s force

in the PW method evaluate muscle endurance after 1

min (80-120 s), and they have high relationships. Sig-

nificant relationships were found between time to 40%

MVC in the CW method and peak force, final force, and

last 30 s force in the PW method. The peak force in the

PW method may be useful in that it is able to evaluate

muscle endurance over a shorter time and without high

pain sensation.

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