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Arm-Curl Field Test for Older Women: Is it a Measure of Arm Strength?

Dunsky, Ayelet; Ayalon, Moshe; Netz, Yael

Journal of Strength and Conditioning Research: January 2011 - Volume 25 - Issue 1 - p 193-197
doi: 10.1519/JSC.0b013e3181bac36a
Original Research
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Ayelet Dunsky, A, Ayalon, M, and Netz, Y. Arm-curl field test for older women: is it a measure of arm strength? J Strength Cond Res 25(1): 193-197, 2011-The facilitative effect of physical activity on age-related decline is well documented. Specifically, it has been found to reduce the risk of dependency. However, physical activity programs for older adults should be carefully designed so that improvements in all aspects of movement and physical capacities are achieved. This means that efficient fitness measurements should be made available for coaches and trainers. The arm-curl test is a common field test known for measuring the strength of upper extremities in older age. The objective of the current study was to determine to what extent this test indeed assesses arm strength as well as other fitness aspects such as arm muscle endurance or general endurance. Scores of the arm-curl test were compared with strength and endurance of elbow flexors measured by an isokinetic dynamometer and general endurance measured by a stress test in 48 independently functioning women (age 72.04 ± 6.28 yr). Significant correlations were indicated between the arm-curl scores and both isokinetic endurance (r = 0.452) and general endurance (r = 0.437); however, a very low nonsignificant correlation was found between the arm-curl and isokinetic maximal strength scores. Coaches must be aware of the fact that the repetitive arm-curl exercise contains a significant aerobic component and thus may contribute to aerobic fitness and arm muscle endurance but not necessarily to arm strength.

Zinman College of Physical Education and Sport Sciences, Wingate Institute, Israel

Address correspondence to Ayelet Dunsky, ayelet@wincol.ac.il.

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Introduction

With increasing age there is loss of muscle function, as manifested by declines in strength, power, and endurance (6,7,12). Strength and endurance of specific muscle groups have a major influence on functional ability of older men and women (1,12,29,32). Low absolute strength, as well as low strength per unit of muscle mass, has been associated with poor physical function (35). Declines in functional abilities could imply, for many older adults, the transition from a state of independence to that of disability (37).

To maintain good health and physical independence, older adults are advised to perform moderate-intensity aerobic activity for a minimum of 30 minutes 5 days a week or vigorous-intensity activity for a minimum of 20 minutes 3 days a week. These activities are in addition to light-intensity activities performed as a part of daily life (for example, walking to the parking lot or shopping). It is also recommended that 8 to 10 strength exercises be performed on at least 2 nonconsecutive days per week using the major muscle groups. The level of resistance used should allow 8 to 12 repetitions (8,15,25).

Arm functions are crucial for executing activities of daily living (ADL) such as carrying groceries, lifting a suitcase, household chores, and picking up grandchildren (21). Deterioration in any of the arm functions, but especially in those that involve elbow flexion, might cause an inability to perform ADL (21,34). Identifying age-related declines in strength and endurance of the arm muscles is therefore of major importance in tracking declines in functional ability.

Most test batteries in this area include components of strength and endurance of the upper extremities. Runnels et al. (29) suggested 3 different laboratory methods for measuring arm strength: isometric, isotonic, and isokinetic. The American College of Sports Medicine (2) suggested 1 repetition maximum (1RM) and 6 to 8RM isotonic protocols using machines as well as free weights. However, this method lacks portability and may be inappropriate with some groups of functionally limited older adults. Because laboratory tests are often expensive and impractical, some researchers have suggested using field tests. Field tests can be used for assessing the upper limit of various specific functional daily life capabilities. For example, the arm-curl test, initiated by Clark (9) as a part of a fitness test for older adults, is a common field test known for assessing strength of the upper extremities (11,14,16-19,26,28,31,33). It records the number of repetitions of elbow flexion and extension performed with a dumbbell in 30 seconds.

However, it is not clear to what extent the arm-curl test actually measures muscle strength. James et al. (18) found a correlation of 0.62 for men and 0.68 for women between arm-curl test scores and 1RM of elbow flexion using the Keiser pneumatic biceps machine. When comparing arm-curl field test scores with overall upper-body strength (which combines 1RM biceps, 1RM chest press, and 1RM seated row), they found a correlation of 0.81 for men and 0.78 for women. On the basis of these results, they considered the arm-curl test to be a measure of overall upper-body strength. Manor et al. (23), on the other hand, indicated that only 21% of the variance in maximal isokinetic strength of elbow flexors was explained by the results of the arm-curl band test. They suggested that this result implies that the arm-curl test incorporates an element other than muscular strength, perhaps muscular endurance.

Assessing strength by a task requiring as many repetitions as possible may incorporate an element of muscle endurance and possibly even general endurance, thus reducing its power as a strength measurement. For example, Netz et al. (27) found that the multiple sit-to-stand test, commonly used as a leg strength test, was predominantly a measure of general endurance and to some extent leg-muscle endurance but not leg strength. Therefore, the present study seeks to assess to what extent the arm-curl test measures arm strength, arm muscle endurance, and possibly other functions such as general endurance.

The subtests included in a field test assessing functional capacity in old age are determined on the basis of the importance of the daily functioning activities they represent. If it is determined that arm strength is essential for daily life and that it is important to include it as a subtest in assessing vital capacity, then the task representing this capacity should represent this and not other capacities. It is therefore essential to determine whether a certain movement indeed represents this function and not other body functioning capacities.

Although field tests are beneficial for assessing upper limits of functional capacities, it is imperative to determine what function is exactly measured by that specific test.

A trainer, especially a personal trainer who intends to focus on a specific body function, should be aware of the information he/she can achieve from that test and build a specific training program specifically targeted to achieve this goal. If a trainer thinks he/she assesses one function and in fact a different function is assessed, the training program will not reflect the physical capacity that meets the real physical need. Furthermore, if minimum/maximum scores to be determined by that test supposedly reflect strength needed for a certain functioning capacity, the scores produced by that test might over or underestimate the real strength level needed for that capacity.

The objective of the current study was therefore to determine to what extent the arm-curl test assesses arm muscle strength as opposed to arm muscle endurance and general endurance. For that purpose, we compared the scores of the arm curl with the following measurements: a) strength and endurance of elbow flexors measured by an isokinetic dynamometer and b) general endurance measured by a stress test assessed by a submaximal graded exercise test performed by walking.

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Methods

Experimental Approach to the Problem

The scores of the field test were compared with scores of well-established laboratory measurements known as a valid tool for assessing arm strength and endurance, and general endurance (concurrent validity).

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Subjects

Forty-eight independently functioning women (72.04 ± 6.28 yr) volunteered to participate in the study (Table 1). They met the following inclusion criteria: a) were ambulatory and b) did not suffer from upper-extremity pain. Each participant underwent a medical screening by a physician, and none were found to manifest significant neurologic, musculoskeletal, or cardiovascular disease. Written informed consent was obtained from each participant, which was approved by the Clinical Science Center Committee on Human Subjects.

Table 1

Table 1

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Instruments

  1. Arm strength and arm endurance were assessed by an isokinetic dynamometer (Biodex Multi-Joint System 2, Biodex Medical Systems, Inc., Shirley, NY, USA). The dynamometer was calibrated according to the manufacturer's protocol before data collection (Biodex Applications/Operations, Biodex Advantage Software 4.0).
  2. Aerobic capacity was assessed by a stress test performed on a treadmill (Clubtrack - 3/0, Quinton, WA, USA) and a 3-lead electrocardiogram (Cardiofax ECG - 6511, N. Kohden, Tokyo, Japan).
  3. An arm-curl field test (9) determined the number of times a 1 kg hand weight could be curled through a full range of motion in 30 seconds.
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Procedures

Each participant performed the stress test while supervised by a physician. This graded walking test, based on treadmill slope and walking speed, was performed according to the Balke protocol (4). Maximum aerobic capacity (V̇O2 peak), a well-established measure of cardiovascular fitness that has been reliably measured in older adults (3), was estimated on the basis of statistical tables specifically designed for prediction of maximum VO2 derived from submaximal scores (2). Scores were calculated in milliliters per kilogram of body weight per minute.

Participants then performed the isokinetic and arm-curl tests in random order. Half of the participants started with the isokinetic tests and the other half with the arm-curl test.

In the isokinetic tests, flexion-extension of the dominant elbow was measured with the participant in a seated position with her back reclined to 110°. The axis of elbow rotation (lateral epicondyle of the humerus) was aligned with the axis of rotation of the dynamometer. Participants were strapped to the chair at the chest, the load cell assembly was attached to the distal forearm by way of a wrist cuff, and the upper arm was secured in place by Velcro straps. After a warm-up of 15 submaximal repetitions to familiarize them with the general set-up and the specific testing velocity, participants rested for 3 minutes, after which they performed a maximal strength test consisting of 5 consecutive cycles of elbow flexion and extension movements. They were instructed to perform flexion only at maximal effort (maximal strength test). After a resting period of 3 minutes, they were asked to perform 30 maximal elbow flexion and extension movements, with an emphasis on the flexors for maximal effort (muscle endurance test). The range of motion was 130°, starting with the elbow fully extended at 180° and ending at 50° at the elbow. Testing velocity was 180°/s. This velocity was selected to match the total time of the muscle endurance test to that of the arm-curl test (approximately 30 s). Furthermore, 180°/s was found to be the most comfortable velocity for the study participants in a pilot study conducted beforehand. The variables measured by the isokinetic dynamometer were torque (N·m) and angle (degrees).

The isokinetic tests used in the current study have been found to be reliable (r = 0.82-0.95) as well as valid for estimating muscular strength in older adults (22,24,36). Peak torque measured with isokinetic tests is routinely referenced as the absolute strength of an individual and is used extensively in studies assessing strength in older adults (5,10,13,20,30). For the maximal strength test, peak force was defined as the highest value of torque developed in 1 of the 5 repetitions. This value was used as the measure of arm strength. For the muscle endurance test, the endurance index was defined as total work performed during 30 repetitions. The total work value served as a measure of arm endurance.

In the arm-curl test, participants sat on a chair and were asked to flex the elbow of their stronger arm as many times as possible in 30 seconds while holding a 1-kg dumbbell. Participants were instructed to maintain a normal breathing pattern and keep their elbow at their side during the entire test. A single repetition consisted of full elbow flexion from maximal extension. The reliability of the arm-curl field test was found to be r = 0.81 (28).

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Statistical Analyses

Four scores were calculated for each participant: aerobic capacity, arm strength, arm endurance, and arm-curl test. A Pearson correlation was used for evaluating correlations between the 4 tests (alpha level for significance p < 0.01). Power analysis was used to determine the number of participants to be recruited for the study (α = 0.05; β = 0.85). This method was based on previous studies reporting assessment of arm muscle tests. The analysis was conducted by R program (http://www.r-project.org) using the MBESS:ss.aipe.R2 procedure, which detects sample size for testing parameter estimation for the multiple correlation coefficient.

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Results

In addition to demographic information, Table 1 presents means and SDs of the 4 test scores. The correlations between the arm-curl test and the isokinetic endurance test and between the arm-curl test and the general endurance test were moderate and significant (r = 0.452, p < 0.01 and r = 0.437, p < 0.01, respectively). However, the correlation between the arm-curl test and the isokinetic maximal strength test was very low and nonsignificant (r = 0.15).

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Discussion

Our findings suggest that the arm-curl assessment does not reflect arm muscle strength. Rather, it incorporates 2 endurance components: arm muscle endurance and general endurance. The inclusion of the arm muscle endurance component in this test is in line with a previous study (23). However, the lack of any strength component in the arm-curl test is inconsistent with the findings of James et al. (18), who found an association between this test and 1RM of elbow flexion as well as between this and the chest press.

These inconsistent findings may stem from the use of different methods for assessing strength. Whereas James and colleagues (18) used isotonic measurement (1RM), we used an isokinetic dynamometer for assessing strength, as did Manor et al. (23). The isokinetic method was found to be more sensitive to age-related changes in elbow strength compared with other methods (29). Furthermore, the isokinetic method is capable of differentiating between maximum strength and arm muscle endurance by assessing them separately. Our finding that the general endurance component of the arm curl (based on the association of its scores with the scores of a submaximal graded exercise test performed by walking on a treadmill) is highly significant and similar to that of arm muscle endurance emphasizes the endurance component of the arm-curl as opposed to the strength component. This finding supports a previous study that used an isokinetic dynamometer to compare leg strength and leg endurance as opposed to a field test known as the leg strength test (27). The findings of that study indicated neither a leg strength nor a leg endurance component in the leg strength field test but did indicate general endurance. Based on the fact that for maximizing strength development only 8 to 12 repetitions of each exercise are recommended (8,15,25), the findings of the present study combined with those in a previous one (27) question the usefulness of tasks requiring as many repetitions as possible within a certain time period for assessing or developing strength. It is possible that strength is not the key component in those particular tasks but rather muscle or general endurance. Therefore, those exercises might even add an additional component to the aerobic activity suggested by the same guidelines as a part of general aerobic ability improvement.

Assuming that the purpose of the arm-curl test is to assess daily functioning, as stated by those using this test (18,19,26,28,31,33), it is questioned whether this test really represents daily functioning. Arm strength is crucial for executing ADL such as carrying groceries, lifting a suitcase, household chores, and picking up grandchildren (21). However, it is unclear whether the arm-curl test indeed represents those daily activities. Further studies are needed to assess the extent to which the arm curl represents such activities.

As in most tests assessing physical capacity, participants' cooperation in the tests applied in this study was personality dependent. Furthermore, the fact that most of our participants were introduced to the isokinetic machine for the first time might have intimidated some of them and could have prevented them from giving their best performance. To minimize such an effect, the protocol of the isokinetic test included 15 submaximal repetitions to familiarize them with the general set-up and the specific testing velocity, as was mentioned earlier.

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Practical Applications

Physical activity trainers must assess their programs to efficiently develop the strength of their clients. To decide on the right measurement to use, they should be aware of the fact that the arm-curl test assesses muscle or general endurance rather than muscle strength. Furthermore, using this test for training purposes might improve their clients' muscle or general endurance but not their strength.

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Keywords:

aging; muscle strength; muscle endurance; general endurance; isokinetic

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