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00005768-201108000-0001900005768_2011_43_1531_marmon_practicing_8miscellaneous-article< 91_0_19_6 >Medicine & Science in Sports & Exercise©2011The American College of Sports MedicineVolume 43(8)August 2011pp 1531-1537Practicing a Functional Task Improves Steadiness with Hand Muscles in Older Adults[APPLIED SCIENCES]MARMON, ADAM R.1; GOULD, JEFFREY R.2; ENOKA, ROGER M.21Department of Physical Therapy, University of Delaware, Newark, DE; and 2Department of Integrative Physiology, University of Colorado at Boulder, Boulder, COAddress for correspondence: Adam R. Marmon, Ph.D., 301 McKinley Lab, Department of Physical Therapy, University of Delaware, Newark, DE 19711; E-mail: marmon@udel.edu.Submitted for publication September 2010.Accepted for publication January 2011.Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (www.acsm-msse.org ).ABSTRACTIntroduction: Improvements in steadiness with practice have been associated with enhanced performance on a functional task in old adults.Purpose: The aims of the study were to examine the specificity of the association between steadiness and a functional task and to assess the influence of practicing a functional task on force steadiness of hand muscles.Methods: Twenty-three older adults (≥70 yr) participated in the study and were assigned to either a practice group (n = 15) or a control group (n = 8). Subjects completed two testing sessions that were 2 wk apart. The practice group completed six additional sessions to practice a functional task (Grooved Pegboard). Tests included maximal voluntary contractions (MVC), force steadiness (precision pinch and index finger abduction) at three target forces (5%, 15%, and 25% MVC), and the Grooved Pegboard test. The associations between strength, steadiness, and the time needed to complete the Grooved Pegboard test were examined. In addition, MVC force, steadiness, and pegboard time were compared between the two testing sessions.Results: The time needed to complete the Grooved Pegboard test was associated with index finger abduction steadiness for two of the three target forces (15% and 25% MVC) but was not associated with pinch steadiness. Practice significantly reduced the time needed to complete the Grooved Pegboard test and improved steadiness in both tasks.Conclusions: Force steadiness provides an appropriate index of hand function, especially when measured at low forces.Studies on the control of movement and the changes that occur with advancing age require experimental constraints that can diminish the functional relevance of the task. One approach used to quantify changes in motor performance across the life span, for example, is to measure an individual's ability to maintain a constant force during contractions with hand muscles (3,6,8). The force exerted by both young and old adults during these tasks is not constant but fluctuates about an average value. These fluctuations are used to denote the steadiness of a contraction and are commonly interpreted as an index of hand function. The magnitude of these fluctuations is often greater for old adults (3,4,17). Some evidence indicates that improvements in steadiness with practice are associated with enhanced performance on a functional task in old adults (7). If this association has functional significance, then improvements in a functional task (Grooved Pegboard test) with practice should also augment force steadiness.Participation in either strength or steadiness training can reduce the magnitude of the fluctuations during steady contractions (5,6). In addition, a recent study (11) on 75 adults (19-89 yr) found that both index finger abduction and pinch grip steadiness (contractions at 5% of maximum) were correlated with one another (r = 0.532, P < 0.001) and with performance on the Grooved Pegboard test (r = 0.572 and r = 0.464, respectively, P < 0.001). The aim of the current study was to investigate the associations between a test of hand function (Grooved Pegboard test) and two measures of hand steadiness (index finger abduction and precision pinch) across a range of target forces (5%, 15%, and 25% of maximum) and the influence of practicing the functional task on steadiness.METHODSTwenty-three old adults (75.0 ± 4.4 yr, range = 71-84 yr; 12 women) participated in this study after informed consent was obtained. All subjects were right-handed (Edinburgh Handedness Inventory) (12), free of neurological disease, and were not taking any medications known to influence neuromuscular function. In addition, none of the subjects reported engaging in activities that required extensive use of the hands for fine motor control. Subjects were assigned to either a practice group (n = 15) or a control group (n = 8). All practice and testing was completed with the left hand. The institutional review board for the University of Colorado at Boulder approved the experimental protocol.Testing procedures.All subjects completed two sessions that each lasted ∼2.5 h and were separated by 2 wk. A testing session comprised measuring, in a counterbalanced order, performance on the Grooved Pegboard test (Lafayette Instruments, Lafayette, IN), maximal voluntary contractions (MVC), and steadiness (expressed as the coefficient of variation for force) in two tasks. The order of testing for each subject was the same in both sessions.The Grooved Pegboard test required subjects to place uniform metal pegs into holes on a board as quickly as possible. The board had 25 holes arranged in 5 rows by 5 columns. The pegs and holes had a keyhole shape, and the orientation of the 25 holes varied across the board (Fig. 1A). Subjects were instructed to fill the entire board one row at a time from right to left and top to bottom. All subjects completed three trials during each testing session. Pegboard performance was expressed as the time needed to fill all 25 holes of the pegboard.FIGURE 1-Experimental setups for the Grooved Pegboard test (A), index finger abduction (B) (figure by Michael A. Pascoe), and precision pinch (C). Panels A and C, adapted from Marmon et al. (11), used with permission. Panel B, adapted from Marmon and Enoka (10), used with permission.Strength and steadiness were measured as the index finger exerted an abduction force and as the thumb and index finger performed a precision pinch grip. The tasks were performed with subjects seated comfortably in a chair, the shoulder abducted by ∼45°, the elbow extended slightly past 90°, and the forearm resting on a table. The index finger measurements were recorded with the hand secured to a custom-fabricated device that maintained the wrist in a neutral position and limited movement of the index finger to the abduction-adduction plane about the metacarpophalangeal joint (Fig. 1B). Index finger abduction forces were measured with three force transducers to account for strength differences across subjects during the maximal contractions and to provide the necessary resolution during the steadiness trials (0.020, 0.201, or 0.425 V·N−1; Model 13 (Sensotec, Columbus, OH)). The precision pinch grip tasks were performed with the forearm in a neutral posture, the styloid process of the ulna resting on the edge of the table, and digits 3-5 flexed (Fig. 1C). Pinch grip forces were recorded using a strain gauge (0.090 V·N−1; Mini-40 (ATI Industrial Automation, Apex, NC)) mounted between two cylinders (2.5-cm diameter; 4-cm length). Subjects held the device between the thumb and index finger.Subjects performed MVC by increasing force from resting to maximum in ∼3 s and then maintaining the maximum force for ∼2 s. Subjects completed no more than five MVC trials, with at least 1 min of rest between trials. The peak value during the MVC trials was taken as the MVC force provided it was within 5% of another trial. Verbal encouragement was given during each trial. Visual feedback was provided (Spike2; Cambridge Electronic Design, Cambridge, UK) on a 17-inch computer monitor placed 1.2 m in front of the subjects at eye level. The force signals were sampled at 1 kHz using an analog-to-digital converter (Power 1401; Cambridge Electronic Design) and stored on a computer for offline analysis.The steady contractions involved maintaining an isometric contraction for 60 s at three target forces (5%, 15%, and 25% MVC force). Visual feedback was provided intermittently (5 s with feedback, 5 s without) using custom software (LabVIEW version 8.2; National Instruments, Austin, TX) that displayed the target force and the force exerted by the subject with a feedback gain of 1.36% MVC force per centimeter. The target force was displayed as a horizontal white line on a black background. The force produced by the subject was shown as a red line that moved across the monitor from left to right during the trial. All subjects affirmed that they were able to see both lines. Subjects completed three force steadiness trials at each target force for the two steadiness tasks.Pegboard practice.Subjects in the practice group completed six additional sessions between the two test sessions. Each practice session comprised 25 trials of the pegboard task. The trials were completed in five blocks of five trials with at least 1 min of rest between each trial and 5 min of rest between each block. The practice sessions were separated by at least 1 d but were no more than 3 d apart. The final practice session was no more than 3 d before the second testing session.Data analysis.Steadiness was quantified over selected segments from the 60-s plateau of each trial (Fig. 2). The plateau comprised six 10-s sweeps, with feedback provided for 5 s of each sweep and removed for the other 5 s. The analysis was performed on the middle four sweeps by using the last 2.3 s of the feedback segment and the first 2.3 s of the no-feedback segment, not including the 600-ms transition period between the two conditions. Steadiness was expressed as the coefficient of variation for force, and only the feedback data are reported because vision was necessary for completing the Grooved Pegboard test. However, the results were not influenced by feedback condition (see Supplemental Digital Content 1, Table, Comparison of Feedback and No Feedback Statistical Outcomes, http://links.lww.com/MSS/ A70). The outcome measure for the pegboard test was the average time to complete the three trials performed in each testing session.FIGURE 2-Force segments that were selected for steadiness analysis. The force exerted by the index finger during a 60-s isometric contraction at a target force of 5% MVC force. Each steadiness trial consisted of six 10-s sweeps, where feedback was intermittently presented (5 s with, 5 s without). The last 2.3 s of the feedback condition and the first 2.3 s of the no-feedback condition, excluding a 0.6-s transition period, were averaged across the middle four sweeps. Marmon and Enoka (10), used with permission.Pearson correlation coefficients were calculated to examine the associations between pegboard time and steadiness in both tasks for the three target forces (5%, 15%, and 25% MVC force) performed by the 23 subjects in the initial testing sessions. To examine differences between the practice and control groups at baseline, independent t-tests were performed for each dependent measure (strength, steadiness, and pegboard time). Changes in steadiness from the initial to final testing session were evaluated separately for each group using two × three repeated-measures ANOVA (two times, before and after; three targets: 5%, 15%, and 25% MVC) for each task. Paired t-tests were used to evaluate strength changes in both tasks from before to after the six practice sessions. Data for one subject at a single target force (25% MVC) from the final testing and from one control subject at a single target (15% MVC) from the initial testing were not available. All statistical analyses were performed with SPSS Statistics (version 16.0.1; SPSS, Inc., Chicago, IL). The α level for all statistical analyses was set at 0.05.RESULTSThe main findings were that time to complete the Grooved Pegboard test and steadiness were associated for two of the three contraction intensities during index finger abduction (15% and 25% MVC), and when an outlier was removed, for two of the three contraction intensities (5% and 15% MVC) for the pinch task. Practice of the Grooved Pegboard test reduced the magnitude of the coefficient of variation for force in both tasks.Associations among strength, steadiness, and the Grooved Pegboard test.The time to complete the Grooved Pegboard test was significantly correlated with the coefficient of variation for force during the steady contractions for the index finger abduction task at 15% MVC (r2 = 0.348, P = 0.004) and 25% MVC (r2 = 0.250, P = 0.018), with a trend toward significance for the 5% MVC target (r2 = 0.138, P = 0.089) (Figs. 3A-C). Pinch steadiness and pegboard time were not significantly correlated for any of the target forces (r2 values ranged from 0.089 to 0.161, P ≥ 0.065). However, there was one outlier whose pinch steadiness performance was consistently >2 SD from the mean (e.g., pinch steadiness at 5% MVC: mean = 2.7% ± 1.5%, 7.9%). When the pinch steadiness performance for this subject was removed, performance in the Grooved Pegboard and pinch steadiness were significantly correlated for the 5% MVC (r2 = 0.194, P = 0.046) and 15% MVC (r2 = 0.242, P = 0.023) target forces, with at trend toward significance for the 25% MVC target (r2 = 0.141, P = 0.093; Figs. 3D-F). The time needed to complete the Grooved Pegboard test was not significantly correlated with strength during either the index abduction task (r2 = 0.027, P = 0.458) or the pinch task (r2 = 0.004, P = 0.786).FIGURE 3-Associations between steadiness at the three target forces and time to complete the Grooved Pegboard test. Steadiness was quantified as the coefficient of variation (CV) for the force exerted during index finger abduction (A-C), which largely involved the first dorsal interosseus (FDI) muscle and during the pinch task (D-F), which involved first dorsal interosseus and other hand muscles. The one subject, whose performance was classified as an outlier during the pinch trials, was removed. The three target forces were 5%, 15%, and 25% MVC. *Statistically significant associations.Changes in pegboard performance.Time to complete the Grooved Pegboard test during the initial testing session was not significantly different between the control and practice groups (83.7 ± 12.0 and 92.5 ± 11.6 s, P = 0.099) (Table 1). Pegboard time did not change for the control group from the initial to final testing session (P = 0.322). Subjects in the practice group, however, reduced pegboard time by 38% (P < 0.001). Changes in pegboard time across the six practice sessions are displayed in Figure 4.TABLE 1. Descriptive statistics for control and practice groups.FIGURE 4-Changes in Grooved Pegboard time for the practice group. Comparison of the time needed to complete the Grooved Pegboard test across sessions (before practice, across six practice sessions, and after practice). Data are mean ± SE. *P ≤ 0.01 relative to the previous session.Changes in strength.Initial MVC forces for the control and practice groups (Table 1) were not statistically different between groups for index finger abduction (P = 0.618) or pinch (P = 0.814). Strength measures did not change for the control group from the initial to the final testing for either the index finger abduction task (P = 0.807) or the pinch task (P = 0.994). Similarly, index finger abduction strength did not change for the practice group (P = 0.449), but pinch strength increased significantly for the practice group (P = 0.015) (Table 1).Changes in steadiness.Initial levels of steadiness were not significantly different between the control and practice groups at any of the three target forces (Table 1) during the index finger abduction task (P ≥ 0.597) or the pinch task (P ≥ 0.186). Steadiness for the control group did not change across the two test sessions at any of the target forces (Table 1) for either the index finger abduction task or the pinch task (P ≥ 0.204 and P ≥ 0.284, respectively). The practice group exhibited significant main effects for time, for both the index finger abduction task (F = 6.826, P = 0.021; observed power = 0.676) and the pinch task (F = 5.688, P = 0.032; observed power = 0.602) (Fig. 5).FIGURE 5-Influence of practice on steadiness (coefficient of variation (CV) for force) at the three target forces. Mean ± SE for before (open bars) and after (filled bars) the six practice sessions. A, Steadiness for index finger abduction (FDI). B, Steadiness for the pinch task. Main effects for time were observed for steadiness during both index finger abduction (P = 0.021) and pinch (P = 0.032) tasks.DISCUSSIONThe goals of the study were to examine the specificity of the association between steadiness and a functional task and to assess the influence of practicing a functional task on force steadiness of hand muscles. In previous work, the coefficient of variation for force during constant-force contractions with hand muscles was associated with the time to complete the Grooved Pegboard test at 5% MVC (11). Whereas the current study did not identify a statistically significant association at 5% MVC, which was likely due to smaller sample size and greater variability in steadiness at lower target forces, there was a trend toward significance. In addition, significant associations between pegboard performance and steadiness were identified at two new target forces (15% and 25% MVC) during index finger abduction but not the pinch task. The current study also reports reductions in pegboard time and increases in steadiness for both the index finger abduction and pinch tasks in response to practice of the Grooved Pegboard task. The decrease in the coefficient of variation for force was largest for the lowest target force (5% MVC) during the index finger abduction task. There were no significant changes observed for the control group.Associations among strength, steadiness, and function.Although measures of steadiness have been studied extensively, the functional relevance of these measures has been uncertain. To address this issue, Marmon et al. (11) found moderate correlations for strength (index finger abduction, pinch, and hand grip) and steadiness (index finger abduction and pinch at 5% MVC force) with performance on two tests of hand function (P ≤ 0.05) in a cohort of 75 adults (19-89 yr). One test was the Grooved Pegboard task and the other test was the game Operation™ (Hasbro, Pawtucket, RI). Findings from the current study expand the specificity of the association between steadiness and time to complete the Grooved Pegboard test to larger target forces (15% and 25% MVC) for index finger abduction. It should be noted that although these associations were moderate, other studies examining the transfer of strength, steadiness, and functional performance tasks have reported similar magnitudes of improvement (6,7,13). Given that the constant abduction force was largely produced by a single hand muscle and the Grooved Pegboard test involved repetitive actions with multiple hand muscles, the finding of a transfer from one task to the other is remarkable. Because some motor units were likely involved in both tasks, one might speculate that the focused activation of the requisite motor units contributed to the transfer of gains from one task to the other. The substantial difference in the number of motor unit pools that could have been activated for each task, however, likely could have to the variability across subjects in the transfer between tasks.Changes in strength and steadiness with practice.Previous investigations have shown that strength training (6,9,16) or practicing steady contractions (7) can reduce the coefficient of variation for force. For example, Kornatz et al. (7) studied the influence of practice on steadiness when the first dorsal interosseus muscle was used to lift and lower a load over a 10° range of motion with steady contractions. The subjects practiced with a light load (∼10% of maximum) during the first 2 wk of the study and then trained for 4 wk with a heavy load (∼70% of maximum). Steadiness, expressed as the SD of acceleration, improved after 2 wk of practice during both shortening (0.245 ± 0.124 to 0.125 ± 0.077 m·s−2, P < 0.001) and lengthening (0.286 ± 0.102 to 0.140 m·s−2, P < 0.001) contractions. However, the final 4 wk of training with the heavier load did not produce any further changes in steadiness (shortening = 0.116 ± 0.084 m·s−2, lengthening = 0.136 ± 0.145 m·s−2). Kornatz et al. (7) also examined the influence of practice and training on a test of manual dexterity, the Purdue pegboard test, which was quantified as the number of pegs inserted into a board in 30 s. At the beginning of the study, there was a significant difference between the right (13 ± 3 pegs) and the left hands (11 ± 3 pegs), but after the 6 wk of practice and training with the left hand, significant improvements were observed for the left hand only (P = 0.004) resulting in similar performance between the two hands.In addition to improving steadiness, the training and practice protocols often evoke significant increases in strength (6,7,9). For example, Kornatz et al. (7) observed progressive strength increases from baseline to 2 wk (0.96 ± 0.43 to 1.38 ± 0.49 kg, P < 0.001) with the light load and again at 6 wk (1.75 ± 0.39 kg, P < 0.001) after training with the heavy load. On the basis of this association, Sosnoff and Newell (15) demonstrated that age-related differences in steadiness were more strongly associated with muscle weakness than with chronological age. Laidlaw et al. (9), however, found that changes in steadiness during index finger abduction were similar for subjects who trained with light (10% MVC) and heavy (80% MVC) loads despite a greater strength gain by the heavy-load group. Similarly, the current study found no statistically significant differences in index finger abduction strength despite an improvement in index finger abduction steadiness.The observed improvements in steadiness must be associated with changes in some features of muscle activation (14,18). Patterns of muscle activation that could improve steadiness, as well as strength, include the coordination of multiple muscles acting together (synergists) or muscles acting in opposition (antagonist coactivation). For example, Laidlaw et al. (9) found that the improvements in strength and steadiness achieved by both the light-load and heavy-load training groups exhibited declines in the average EMG amplitude, suggesting that the reduction in the coefficient of variation for force during the steadiness trials could be attributed to altered patterns of agonist and antagonist activation. One candidate underlying improvements in steadiness is a reduction in the variability of the discharge times by the activated motor units as force fluctuations are influenced by variability in discharge times (1) and decreases in pegboard time were associated with reductions in the variability of motor unit discharge (7).One reason why the improvements in steadiness in the current study were largest for the lowest target force may be the association between variability in motor unit discharge rate and steadiness (1). Because the contributions of individual motor units to the net force exerted by a muscle are greatest at low forces (2), relatively minor decreases in motor unit discharge variability due to practicing the pegboard practice would be most effective at reducing the magnitude of the force fluctuations at the lowest target forces.The current findings provide further support for the use of force steadiness as an index of hand function, especially using index finger abduction as a surrogate for fine motor performance of the hand. The improvements observed in both steadiness and the time needed to complete the Grooved Pegboard test after the pegboard practice, without improvements in strength, suggest that similar neuromuscular adaptations are involved in both tasks. Continued study of the factors responsible for differences in steadiness will provide insight into mechanisms responsible for changes in motor performance across the adult life span.CONCLUSIONSThe current study examined the influence of practicing a functional hand task on force steadiness of hand muscles. The choice of the Grooved Pegboard test for the functional task was based on previous findings (11) that showed moderate associations between the Grooved Pegboard test and steadiness during both index finger abduction and pinch tasks. As low-force muscle contractions are used during the Grooved Pegboard test, transference of improvement in the Grooved Pegboard test was largest for the lowest target force during the steady contractions.This work was supported by AG09000 to R.M. Enoka and T32 AG00279 awarded to Robert Schwartz that supported A. R. Marmon.Funding received for this work is from the National Institutes of Health.The authors have no conflict of interest.The results of the present study do not constitute endorsement by the American College of Sports Medicine.REFERENCES1. Barry BK, Pascoe MA, Jesunathadas M, Enoka RM. Rate coding is compressed but variability is unaltered for motor units in a hand muscle of old adults. J Neurophysiol. 2007;97(5):3206-18. [CrossRef] [Medline Link] [Context Link]2. Fuglevand AJ, Winter DA, Patla AE. Models of recruitment and rate coding organization in motor-unit pools. J Neurophysiol. 1993;70(6):2470-88. [Context Link]3. Galganski ME, Fuglevand AJ, Enoka RM. Reduced control of motor output in a human hand muscle of elderly subjects during submaximal contractions. J Neurophysiol. 1993;69(6):2108-15. [Medline Link] [Context Link]4. Graves AE, Kornatz KW, Enoka RM. Older adults use a unique strategy to lift inertial loads with the elbow flexor muscles. J Neurophysiol. 2000;83(4):2030-9. 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[Context Link] AGING; GROOVED PEGBOARD; PRACTICE; HAND FUNCTIONovid.com:/bib/ovftdb/00005768-201108000-0001900005073_2007_97_3206_barry_variability_|00005768-201108000-00019#xpointer(id(R1-19))|11065213||ovftdb|SL00005073200797320611065213P65[CrossRef]10.1152%2Fjn.01280.2006ovid.com:/bib/ovftdb/00005768-201108000-0001900005073_2007_97_3206_barry_variability_|00005768-201108000-00019#xpointer(id(R1-19))|11065405||ovftdb|SL00005073200797320611065405P65[Medline Link]17360826ovid.com:/bib/ovftdb/00005768-201108000-0001900005073_1993_69_2108_galganski_contractions_|00005768-201108000-00019#xpointer(id(R3-19))|11065405||ovftdb|SL00005073199369210811065405P67[Medline Link]8350134ovid.com:/bib/ovftdb/00005768-201108000-0001900005073_2000_83_2030_graves_strategy_|00005768-201108000-00019#xpointer(id(R4-19))|11065405||ovftdb|SL00005073200083203011065405P68[Medline 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