- Email: [email protected]
A practical posture for hand grip dynamometry in the clinical setting
ARTICLE IN PRESS Clinical Nutrition (2005) 24, 224–228
http://intl.elsevierhealth.com/journals/clnu
ORIGINAL ARTICLE
A practical posture for hand grip dynamometry in the clinical setting T.E. Hillmana, Q.M. Nunesa, S.T. Hornbya, Z. Stangab, K.R. Nealc, B.J. Rowlandsa, S.P. Allisond, D.N. Loboa, a
Section of Surgery, Queen’s Medical Centre, University Hospital, Nottingham NG7 2UH, UK Department of Internal Medicine, Inselspital, Berne, Switzerland c Department of Public Health Medicine and Epidemiology, Queen’s Medical Centre, University Hospital, Nottingham, UK d Clinical Nutrition Unit, Queen’s Medical Centre, University Hospital, Nottingham, UK b
Received 2 August 2004; accepted 9 September 2004
KEYWORDS Hand grip dynamometry; Grip strength; Posture; Reproducibility; Nutritional assessment; Function
Summary Background & Aims: The optimal testing position for hand grip strength, which is a useful functional measure of nutritional status, is open to debate. We therefore examined the systematic difference between different postures in order to establish a methodology that is clinically relevant, easy to perform and reproducible. Methods: Grip strength was measured in the dominant and non-dominant hands with a strain gauge dynamometer in three positions: lying at 301 in bed with elbows supported, seated in an armchair with elbows supported and in a chair with elbows unsupported. The average of three readings made in each position, each 1 min apart, was recorded. Results: 55 normally nourished subjects (26 male) were studied. Mean (95% CI) grip strengths measured in the dominant hand with the subject in bed, sitting in an armchair and sitting in a chair were 45.7 (42.3–49.2), 46.3 (42.9–49.8) and 48.5 (45.4–51.7) kg, respectively for males. Corresponding values for females were 29.4 (27.0–31.8), 29.3 (26.8–31.9) and 31.6 (28.8–34.3) kg. There was no significant difference (Student t-paired test) between measurements made in bed and on an armchair (P ¼ 0:49), but the measurements made in a chair were significantly higher than those made in bed (P ¼ 0:001) and in an armchair (P ¼ 0:004). No statistical difference was present, comparing the three separate measurements in each position (Student t-paired test). Conclusions: Measurement of grip strength using hand dynamometry is reproducible and consistent. As all patients are not able to sit in a chair with elbows
Corresponding author. Tel.: +44 115 970 9245; fax: +44 115 970 9428.
E-mail address: [email protected] (D.N. Lobo). 0261-5614/$ - see front matter & 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.clnu.2004.09.013
ARTICLE IN PRESS Posture for hand grip dynamometry
225
unsupported, in clinical practice it is more practicable to perform hand dynamometry with the elbows supported in a bed or armchair. & 2004 Elsevier Ltd. All rights reserved.
Introduction Hand grip strength measurement is useful in functional nutritional assessment and is sensitive to short-term changes in nutritional status.1,2 There are several factors influencing the degree of strength generated and reproducibility of grip strength measurements and attempts have been made to standardise the methodology for measuring grip strength. The American Society of Hand Therapists in 1981 suggested a testing protocol in which the subject is seated with the shoulder adducted and neutrally rotated, the elbow flexed at 901 and the forearm and wrist in the neutral position.3 However, there is no consensus on the optimal body posture or positions of shoulder, elbow and wrist for measuring hand grip strength. Teraoka4 and Balogun et al.5 found that grip strength was greater in the standing than in the sitting position. Hazleton et al.6 found a slight increase in grip strength at 211 ulnar deviation or 141 radial deviation at the wrist while Purswell and Terell7 reported a 15% reduction in grip strength at 201 ulnar deviation and 18% reduction at 201 radial deviation as compared to the neutral position. According to O’Driscoll et al.,8 the optimum position for the wrist is 33–401 extension and 71 ulnar deviation. Mathiowetz et al.9 studied the effect of elbow position on grip strength and found it to be higher with the elbow flexed at 901 while Su et al.10 found that the highest mean grip strength score was obtained with the elbow fully extended. In the clinical setting there are a number of reasons why it may not be possible to follow standardised testing procedures. In this study we have measured hand grip strength in normal subjects in the supine and sitting (armchair with elbows supported and chair with elbows unsupported) positions in order to establish a methodology that is clinically relevant, easy to perform and reproducible.
Methods Hand grip dynamometry was performed on 55 normal subjects (26 male, 29 female). Subjects with known medical disease, ongoing treatment and hand pain or upper limb deformities were excluded. The height of each subject was recorded to the nearest 0.01 m, weight measured to the
Figure 1 Subject in bed with elbows supported.
Figure 2 Subject in armchair with elbows supported.
nearest 0.1 kg using Avery 3306ABV scales (Avery Berkel, Royston, UK), and body mass index calculated. Grip strength was measured with a strain gauge dynamometer (Department of Medical Physics, Queen’s Medical Centre, Nottingham, UK). The forearm was placed with the elbow in 901 flexion and the wrist in the neutral position. Measurements were made in the dominant and non-dominant
ARTICLE IN PRESS 226
T.E. Hillman et al.
hands with the shoulder adducted and neutrally rotated in three positions: lying at 301 in bed with elbows supported, seated in an armchair with elbows supported and in a chair with elbows unsupported (Figs. 1–3). Three readings were made in each position, each 1 min apart, and the average of the three were calculated. Data were expressed as Mean (95% CI) and statistical analysis was performed using SPSSs for WindowsTM Release 11.0 software (SPSS, Inc., Chicago, USA). Data were tested for statistical significance using the
Student t-paired and unpaired tests and differences were considered significant at Po0:05: The design of this study was approved by the ethics committee of University Hospital, Nottingham and subjects were recruited after obtaining verbal consent.
Results The demographic profile of the 55 subjects is summarised in Table 1 and measurements of hand grip strength in males and females in the three positions are listed in Table 2. Grip strength was significantly greater in males than in females and in
Table 2 Hand grip strength (kg) measured in males and females in the three positions. Position Bed Dominant hand Nondominant hand Armchair Dominant hand Nondominant hand Chair Dominant hand Nondominant hand
Female (n ¼ 29)
45.7 (42.3–49.2) 29.4 (27.0–31.8) 43.4 (40.0–46.1) 28.0 (25.5–30.6)
46.3 (42.9–49.8) 29.3 (26.8–31.9) 43.4 (40.0–46.1) 28.0 (25.5–30.6)
48.5 (45.4–51.7) 31.6 (28.8–34.3) 45.9 (43.3–48.6) 30.0 (27.4–32.6)
All values are mean (95% CI). Dominant vs. non-dominant hand Po0.001 for all positions (Student t-paired test). Male vs. female Po0.001 for all positions [Student t-test (unpaired)].
Figure 3 Subject in chair with elbows unsupported.
Table 1
Male (n ¼ 26)
Demographic profile of subjects.
Age (yr) Weight (kg) Height (m) Body mass index (kg/m2) All values are Mean (95% CI).
Male (n ¼ 26)
Female (n ¼ 29)
34.0 80.9 1.78 26.6
36.4 65.1 1.62 24.7
(26.6–41.6) (77.2–84.5) (1.75–1.81) (24.4–26.8)
(28.8–44.1) (62.1–68.0) (1.60–1.65) (23.5–25.9)
ARTICLE IN PRESS
0.78 0.77
227 the dominant than in the non-dominant hand (Po0:001). Statistical significance was not attained when the paired differences between the three measurements performed in each position were compared (Table 3). While there was no significant difference when measurements made in bed were compared with those made in an armchair, measurements made in a chair were significantly greater than those made in bed and in an armchair for both the dominant and non-dominant hands (Table 4).
Discussion
*P calculated using Student t-paired test (n ¼ 55).
0.35 0.76
0.14
0.49
0.42
0.62
0.63
Test 2–3 0.1 (1.2–0.9) Test 1–3 0.1 (0.9–1.2) Test 1–2 0.3 (0.9–1.5) Test 1–3 0.5 (0.6–1.7) Test 1–2 0.2 (1.1–0.8)
Paired tests Mean difference in kg (95% CI) P*
Test 2–3 0.7 (0.2–1.6)
Test 1–2 0.3 (1.2–0.6)
Test 1–3 0.5 (1.8–0.8)
Test 2–3 0.2 (1.1–0.7)
Chair Armchair Bed Position
Table 3
Comparison between the grip strength measured on each of the three occasions in the three positions in the dominant hand.
Posture for hand grip dynamometry
Although early mobilisation of patients is desirable, some who are acutely or chronically ill spend most of their time either supine in bed or in an armchair. Their body posture may vary depending on the stage of the disease which makes it difficult to compare the results of hand grip dynamometry. We therefore tested normal subjects in the supine and sitting positions in order to establish a more clinically useful methodology. In our study the grip strength was highest when subjects were seated in a chair with their elbows unsupported (Table 2). This is consistent with the studies by Balogun et al.5 and Kuzala and Vargo.11 The resting position of the elbow is 701 flexion12 and muscles tend to be strongest at lengths just greater than their maximal resting lengths.13 In this position there is optimal overlap between the actin and myosin filaments.14,15 In our study statistical significance was not attained when the paired differences between the three measurements performed in each position were compared indicating that measurements in each of the three postures were reproducible (Table 3). There was no statistically significant difference (P ¼ 0:49) when measurements made with the elbow supported in bed were compared with those made in an armchair, while measurements made in a chair with the elbow unsupported were significantly greater than those made in bed (P ¼ 0:001) and in an armchair (P ¼ 0:004) (Table 4). When the upper limb is not supported, grip strength becomes stronger due to the synergistic actions of other muscles, but this is variable.8,16 Also with the forearm and wrist properly stabilized, between-day grip strength measurements are highly repeatable.17 We, therefore, recommend that in the clinical situation, grip strength should be measured with the elbows supported in bed or in an armchair rather than in a chair with the elbows unsupported.
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T.E. Hillman et al.
Table 4 Comparison between the grip strength measured in the three positions in the dominant and nondominant hands. Paired differences
Mean difference (kg)
95% CI
P*
Dominant hand Armchair–chair Bed–chair Armchair–bed
2.2 2.5 0.2
3.7–0.7 3.8–1.1 0.4–0.9
0.004 0.001 0.49
Non-dominant hand Armchair–chair Bed–chair Armchair–bed
1.9 2.1 0.2
3.1–0.7 3.2–0.9 0.6–1.0
0.003 0.001 0.57
*P calculated using Student t-paired test (n ¼ 55).
References 1. Jeejeebhoy KN. The functional basis of nutritional assessment. In: Kinney JM, Jeejeebhoy KN, Hill GL, Owen OE editors. Nutrition and metabolism in patient care. Philadelphia: WB Saunders; 1988. p. 739–51. 2. Windsor JA, Hill GL. Grip strength: a measure of the proportion of protein loss in surgical patients. Br J Surg 1998;75:880–2. 3. Fess EE, Moran C. Clinical assessment recommendations. Indianapolis: American Society of Hand Therapists Monograph; 1981. 4. Teraoka T. Studies on the peculiarity of grip strength in relation to body positions and aging. Kobe J Med Sci 1979;25:1–17. 5. Balogun JA, Akomolafe CT, Amusa LO. Grip strength: effects of testing posture and elbow position. Arch Phys Med Rehabil 1991;72:280–3. 6. Hazelton FT, Schmidt GL, Flatt AE, Stephens RI. The influence of wrist position on the force produced by the finger flexors. J Biomech 1975;8:301–6. 7. Purswell JL, Terrel R. The influence of forearm and wrist orientation on static grip strength as a design criterion for hand tools. Proceedings of the sixth congress of the International Ergonomics Association, 1976. p. 28–32. 8. O’Driscoll SW, Horii E, Ness R, Cahalan TD, Richards RR, An KN. The relationship between wrist position, grasp size, and grip strength. J Hand Surg 1992;17:169–77.
9. Mathiowetz V, Rennells C, Donahoe L. Effect of elbow position on grip and key pinch strength. J Hand Surg 1985;10:694–7. 10. Su CY, Lin JH, Chien TH, Cheng KF, Sung YT. Grip strength in different positions of elbow and shoulder. Arch Phys Med Rehabil 1994;75:812–5. 11. Kuzala EA, Vargo MC. The relationship between elbow position and grip strength. Am J Occup Ther 1992;46:509–12. 12. Kaltenborn FM. Mobilisation of the extremity of the joints, 3rd ed. Oslo: Olaf Norlis Bokhandel Universitetsgaten; 1980 (pp. 86–91). 13. Lamb DR. Physiology of exercise: responses and adaptations, 2nd ed. New York: MacMillan; 1984 (pp. 242–268). 14. Josephson RK. Extensive and intensive factors determining the performance of striated muscle. J Exp Zool 1975;194:135–53. 15. Zierlger KL. Mechanism of muscle contraction and its energetics. In: Mouncastle VB editor. Medical physiology. 13th ed. St. Louis: Mosby; 1974. p. 77–120. 16. Swanson AB, Matev IB, de Groot G. The strength of the hand. Bull Prosthet Res 1970;10:145–53. 17. Fong PWK, Ng GYF. Effect of wrist positioning on the repeatability and strength of power grip. Am J Occup Ther 2001;55:212–6.
http://intl.elsevierhealth.com/journals/clnu
ORIGINAL ARTICLE
A practical posture for hand grip dynamometry in the clinical setting T.E. Hillmana, Q.M. Nunesa, S.T. Hornbya, Z. Stangab, K.R. Nealc, B.J. Rowlandsa, S.P. Allisond, D.N. Loboa, a
Section of Surgery, Queen’s Medical Centre, University Hospital, Nottingham NG7 2UH, UK Department of Internal Medicine, Inselspital, Berne, Switzerland c Department of Public Health Medicine and Epidemiology, Queen’s Medical Centre, University Hospital, Nottingham, UK d Clinical Nutrition Unit, Queen’s Medical Centre, University Hospital, Nottingham, UK b
Received 2 August 2004; accepted 9 September 2004
KEYWORDS Hand grip dynamometry; Grip strength; Posture; Reproducibility; Nutritional assessment; Function
Summary Background & Aims: The optimal testing position for hand grip strength, which is a useful functional measure of nutritional status, is open to debate. We therefore examined the systematic difference between different postures in order to establish a methodology that is clinically relevant, easy to perform and reproducible. Methods: Grip strength was measured in the dominant and non-dominant hands with a strain gauge dynamometer in three positions: lying at 301 in bed with elbows supported, seated in an armchair with elbows supported and in a chair with elbows unsupported. The average of three readings made in each position, each 1 min apart, was recorded. Results: 55 normally nourished subjects (26 male) were studied. Mean (95% CI) grip strengths measured in the dominant hand with the subject in bed, sitting in an armchair and sitting in a chair were 45.7 (42.3–49.2), 46.3 (42.9–49.8) and 48.5 (45.4–51.7) kg, respectively for males. Corresponding values for females were 29.4 (27.0–31.8), 29.3 (26.8–31.9) and 31.6 (28.8–34.3) kg. There was no significant difference (Student t-paired test) between measurements made in bed and on an armchair (P ¼ 0:49), but the measurements made in a chair were significantly higher than those made in bed (P ¼ 0:001) and in an armchair (P ¼ 0:004). No statistical difference was present, comparing the three separate measurements in each position (Student t-paired test). Conclusions: Measurement of grip strength using hand dynamometry is reproducible and consistent. As all patients are not able to sit in a chair with elbows
Corresponding author. Tel.: +44 115 970 9245; fax: +44 115 970 9428.
E-mail address: [email protected] (D.N. Lobo). 0261-5614/$ - see front matter & 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.clnu.2004.09.013
ARTICLE IN PRESS Posture for hand grip dynamometry
225
unsupported, in clinical practice it is more practicable to perform hand dynamometry with the elbows supported in a bed or armchair. & 2004 Elsevier Ltd. All rights reserved.
Introduction Hand grip strength measurement is useful in functional nutritional assessment and is sensitive to short-term changes in nutritional status.1,2 There are several factors influencing the degree of strength generated and reproducibility of grip strength measurements and attempts have been made to standardise the methodology for measuring grip strength. The American Society of Hand Therapists in 1981 suggested a testing protocol in which the subject is seated with the shoulder adducted and neutrally rotated, the elbow flexed at 901 and the forearm and wrist in the neutral position.3 However, there is no consensus on the optimal body posture or positions of shoulder, elbow and wrist for measuring hand grip strength. Teraoka4 and Balogun et al.5 found that grip strength was greater in the standing than in the sitting position. Hazleton et al.6 found a slight increase in grip strength at 211 ulnar deviation or 141 radial deviation at the wrist while Purswell and Terell7 reported a 15% reduction in grip strength at 201 ulnar deviation and 18% reduction at 201 radial deviation as compared to the neutral position. According to O’Driscoll et al.,8 the optimum position for the wrist is 33–401 extension and 71 ulnar deviation. Mathiowetz et al.9 studied the effect of elbow position on grip strength and found it to be higher with the elbow flexed at 901 while Su et al.10 found that the highest mean grip strength score was obtained with the elbow fully extended. In the clinical setting there are a number of reasons why it may not be possible to follow standardised testing procedures. In this study we have measured hand grip strength in normal subjects in the supine and sitting (armchair with elbows supported and chair with elbows unsupported) positions in order to establish a methodology that is clinically relevant, easy to perform and reproducible.
Methods Hand grip dynamometry was performed on 55 normal subjects (26 male, 29 female). Subjects with known medical disease, ongoing treatment and hand pain or upper limb deformities were excluded. The height of each subject was recorded to the nearest 0.01 m, weight measured to the
Figure 1 Subject in bed with elbows supported.
Figure 2 Subject in armchair with elbows supported.
nearest 0.1 kg using Avery 3306ABV scales (Avery Berkel, Royston, UK), and body mass index calculated. Grip strength was measured with a strain gauge dynamometer (Department of Medical Physics, Queen’s Medical Centre, Nottingham, UK). The forearm was placed with the elbow in 901 flexion and the wrist in the neutral position. Measurements were made in the dominant and non-dominant
ARTICLE IN PRESS 226
T.E. Hillman et al.
hands with the shoulder adducted and neutrally rotated in three positions: lying at 301 in bed with elbows supported, seated in an armchair with elbows supported and in a chair with elbows unsupported (Figs. 1–3). Three readings were made in each position, each 1 min apart, and the average of the three were calculated. Data were expressed as Mean (95% CI) and statistical analysis was performed using SPSSs for WindowsTM Release 11.0 software (SPSS, Inc., Chicago, USA). Data were tested for statistical significance using the
Student t-paired and unpaired tests and differences were considered significant at Po0:05: The design of this study was approved by the ethics committee of University Hospital, Nottingham and subjects were recruited after obtaining verbal consent.
Results The demographic profile of the 55 subjects is summarised in Table 1 and measurements of hand grip strength in males and females in the three positions are listed in Table 2. Grip strength was significantly greater in males than in females and in
Table 2 Hand grip strength (kg) measured in males and females in the three positions. Position Bed Dominant hand Nondominant hand Armchair Dominant hand Nondominant hand Chair Dominant hand Nondominant hand
Female (n ¼ 29)
45.7 (42.3–49.2) 29.4 (27.0–31.8) 43.4 (40.0–46.1) 28.0 (25.5–30.6)
46.3 (42.9–49.8) 29.3 (26.8–31.9) 43.4 (40.0–46.1) 28.0 (25.5–30.6)
48.5 (45.4–51.7) 31.6 (28.8–34.3) 45.9 (43.3–48.6) 30.0 (27.4–32.6)
All values are mean (95% CI). Dominant vs. non-dominant hand Po0.001 for all positions (Student t-paired test). Male vs. female Po0.001 for all positions [Student t-test (unpaired)].
Figure 3 Subject in chair with elbows unsupported.
Table 1
Male (n ¼ 26)
Demographic profile of subjects.
Age (yr) Weight (kg) Height (m) Body mass index (kg/m2) All values are Mean (95% CI).
Male (n ¼ 26)
Female (n ¼ 29)
34.0 80.9 1.78 26.6
36.4 65.1 1.62 24.7
(26.6–41.6) (77.2–84.5) (1.75–1.81) (24.4–26.8)
(28.8–44.1) (62.1–68.0) (1.60–1.65) (23.5–25.9)
ARTICLE IN PRESS
0.78 0.77
227 the dominant than in the non-dominant hand (Po0:001). Statistical significance was not attained when the paired differences between the three measurements performed in each position were compared (Table 3). While there was no significant difference when measurements made in bed were compared with those made in an armchair, measurements made in a chair were significantly greater than those made in bed and in an armchair for both the dominant and non-dominant hands (Table 4).
Discussion
*P calculated using Student t-paired test (n ¼ 55).
0.35 0.76
0.14
0.49
0.42
0.62
0.63
Test 2–3 0.1 (1.2–0.9) Test 1–3 0.1 (0.9–1.2) Test 1–2 0.3 (0.9–1.5) Test 1–3 0.5 (0.6–1.7) Test 1–2 0.2 (1.1–0.8)
Paired tests Mean difference in kg (95% CI) P*
Test 2–3 0.7 (0.2–1.6)
Test 1–2 0.3 (1.2–0.6)
Test 1–3 0.5 (1.8–0.8)
Test 2–3 0.2 (1.1–0.7)
Chair Armchair Bed Position
Table 3
Comparison between the grip strength measured on each of the three occasions in the three positions in the dominant hand.
Posture for hand grip dynamometry
Although early mobilisation of patients is desirable, some who are acutely or chronically ill spend most of their time either supine in bed or in an armchair. Their body posture may vary depending on the stage of the disease which makes it difficult to compare the results of hand grip dynamometry. We therefore tested normal subjects in the supine and sitting positions in order to establish a more clinically useful methodology. In our study the grip strength was highest when subjects were seated in a chair with their elbows unsupported (Table 2). This is consistent with the studies by Balogun et al.5 and Kuzala and Vargo.11 The resting position of the elbow is 701 flexion12 and muscles tend to be strongest at lengths just greater than their maximal resting lengths.13 In this position there is optimal overlap between the actin and myosin filaments.14,15 In our study statistical significance was not attained when the paired differences between the three measurements performed in each position were compared indicating that measurements in each of the three postures were reproducible (Table 3). There was no statistically significant difference (P ¼ 0:49) when measurements made with the elbow supported in bed were compared with those made in an armchair, while measurements made in a chair with the elbow unsupported were significantly greater than those made in bed (P ¼ 0:001) and in an armchair (P ¼ 0:004) (Table 4). When the upper limb is not supported, grip strength becomes stronger due to the synergistic actions of other muscles, but this is variable.8,16 Also with the forearm and wrist properly stabilized, between-day grip strength measurements are highly repeatable.17 We, therefore, recommend that in the clinical situation, grip strength should be measured with the elbows supported in bed or in an armchair rather than in a chair with the elbows unsupported.
ARTICLE IN PRESS 228
T.E. Hillman et al.
Table 4 Comparison between the grip strength measured in the three positions in the dominant and nondominant hands. Paired differences
Mean difference (kg)
95% CI
P*
Dominant hand Armchair–chair Bed–chair Armchair–bed
2.2 2.5 0.2
3.7–0.7 3.8–1.1 0.4–0.9
0.004 0.001 0.49
Non-dominant hand Armchair–chair Bed–chair Armchair–bed
1.9 2.1 0.2
3.1–0.7 3.2–0.9 0.6–1.0
0.003 0.001 0.57
*P calculated using Student t-paired test (n ¼ 55).
References 1. Jeejeebhoy KN. The functional basis of nutritional assessment. In: Kinney JM, Jeejeebhoy KN, Hill GL, Owen OE editors. Nutrition and metabolism in patient care. Philadelphia: WB Saunders; 1988. p. 739–51. 2. Windsor JA, Hill GL. Grip strength: a measure of the proportion of protein loss in surgical patients. Br J Surg 1998;75:880–2. 3. Fess EE, Moran C. Clinical assessment recommendations. Indianapolis: American Society of Hand Therapists Monograph; 1981. 4. Teraoka T. Studies on the peculiarity of grip strength in relation to body positions and aging. Kobe J Med Sci 1979;25:1–17. 5. Balogun JA, Akomolafe CT, Amusa LO. Grip strength: effects of testing posture and elbow position. Arch Phys Med Rehabil 1991;72:280–3. 6. Hazelton FT, Schmidt GL, Flatt AE, Stephens RI. The influence of wrist position on the force produced by the finger flexors. J Biomech 1975;8:301–6. 7. Purswell JL, Terrel R. The influence of forearm and wrist orientation on static grip strength as a design criterion for hand tools. Proceedings of the sixth congress of the International Ergonomics Association, 1976. p. 28–32. 8. O’Driscoll SW, Horii E, Ness R, Cahalan TD, Richards RR, An KN. The relationship between wrist position, grasp size, and grip strength. J Hand Surg 1992;17:169–77.
9. Mathiowetz V, Rennells C, Donahoe L. Effect of elbow position on grip and key pinch strength. J Hand Surg 1985;10:694–7. 10. Su CY, Lin JH, Chien TH, Cheng KF, Sung YT. Grip strength in different positions of elbow and shoulder. Arch Phys Med Rehabil 1994;75:812–5. 11. Kuzala EA, Vargo MC. The relationship between elbow position and grip strength. Am J Occup Ther 1992;46:509–12. 12. Kaltenborn FM. Mobilisation of the extremity of the joints, 3rd ed. Oslo: Olaf Norlis Bokhandel Universitetsgaten; 1980 (pp. 86–91). 13. Lamb DR. Physiology of exercise: responses and adaptations, 2nd ed. New York: MacMillan; 1984 (pp. 242–268). 14. Josephson RK. Extensive and intensive factors determining the performance of striated muscle. J Exp Zool 1975;194:135–53. 15. Zierlger KL. Mechanism of muscle contraction and its energetics. In: Mouncastle VB editor. Medical physiology. 13th ed. St. Louis: Mosby; 1974. p. 77–120. 16. Swanson AB, Matev IB, de Groot G. The strength of the hand. Bull Prosthet Res 1970;10:145–53. 17. Fong PWK, Ng GYF. Effect of wrist positioning on the repeatability and strength of power grip. Am J Occup Ther 2001;55:212–6.