ReviewHand grip strength: Outcome predictor and marker of nutritional status
Introduction
Impaired muscle strength is a well-known phenomenon occurring in disease-related malnutrition. Reduced nutritional intake results in a compensatory loss of whole body protein which is preferably lost from muscle mass, the body’s largest protein reserve.3, 4 Simultaneously, muscle protein synthesis can also be reduced in disease-related malnutrition.
Since muscle function correlates closely with whole body protein,10, 11 body cell mass,12 anthropometrically measured arm muscle mass,13 and even with body mass index (BMI),14, 15 loss of weight or muscle mass invariably results in decreased muscle strength, i.e. weakness, which is reflected in deteriorating function tests as well as in prominently altered muscle morphology.
Reduced muscle strength is in turn associated with loss of physical functionality and with negative impact on recovery of health after illness or surgery, which partly explains the high predictive power of muscle function tests. Various studies have shown a close correlation between muscle strength and outcome in acute and chronic disease.16, 17, 18, 19
Section snippets
Measurement of hand grip strength as indicator of muscle function
Just as measuring body composition offers a qualitative aspect of nutritional status, muscle function represents a dynamic indicator of muscle mass. Measurement of muscle function as indicator of functional as well as nutritional status has therefore gained considerable attention in the past years. There are several methods for the measurement of voluntary and involuntary muscle function. Electrical stimulation at various frequencies but constant isometric length is used for the determination
Determinants of hand grip strength
In healthy people, age and gender are the strongest influencing factors on hand grip strength.25 In acute or chronic disease, however, various further factors such as disease severity, co-morbidity load, medical treatment, and immobilisation contribute to a certain extent to muscle weakness and therefore to the patients’ decreased well-being. Bed rest and muscle disuse,26 inflammation, infection, endotoxemia, corticosteroids, muscle relaxants, hypoxia, electrolyte imbalances and oxidative
Muscle function in obese subjects
There are several reasons why muscle strength might be affected in obesity. Obese subjects have greater muscle mass which is a major determinant of muscle strength, at least in normal weight subjects. Also, a certain training effect induced by bearing and supporting the higher weight can strengthen the muscles of obese subjects. On the other hand, high body weight is associated with decreased sedentary lifestyle,30 as well as reduced physical activity and mobility. Moreover, higher weight
Changes of muscle morphology and function in malnutrition
The alterations in muscle morphology found in malnutrition are well described. Muscle biopsy specimens of untreated anorectics,35, 36, 37 of children with malnutrition38 and even of morbidly obese patients after two weeks of starvation7 consistently show myopathic changes with selective type II fibre (anaerobic, glycolytic, fast twitch) atrophy. Also, Z band degeneration is found in malnutrition.7, 39 These principal ultra structural changes in muscle have been suggested to reflect loss of
Outcome associated with impaired muscle function
The predictive power of muscle function, and hand grip strength in particular, has been demonstrated in numerous clinical as well as epidemiological studies (see Table 1).
In disease, reduced muscle function has severe consequences for functional status, recovery from disease and clinical outcome, particularly as several further factors may also interact.
Reduced hand grip strength was early shown to be strongly correlated with postoperative complications18, 19, 46 and has also been reported to
Hand grip strength as predictor of bone mass
There is a known site specific effect between muscle mass and strength and bone mineral density (BMD) as the torque placed on bone by muscle contraction strengthens the bone.57, 58 This is clinically relevant in the case of knee extension strength and total hip BMD e.g. since muscle weakness is a possible contributing risk factor for falls59, 60 and low BMD a clinical predictor for increased risk of fracture in falls.
Similarly, hand grip strength functions as indicator of hand BMD in adults,61,
Hand grip strength as nutritional outcome variable
Since muscle function reacts earlier to nutritional deprivation as well as restoration than muscle mass, as described above, it is obviously very tempting to employ hand grip strength as target variable for detecting and monitoring changes in nutritional status (see Table 2). Christie and coworkers demonstrated rapid improvement of various muscle function tests including voluntary hand grip strength in 41 severely malnourished IBD patients undergoing a 14 day intervention with total parenteral
Limitations and controversies related to hand grip strength
Some limitations related to the measurement of hand grip strength must also be addressed. There is still e.g. no consensus on measurement protocols.92 The American Society of Hand therapists93 proposes assessment of grip strength with the elbow flexed at 90° with the subject in the sitting position, with their shoulders adducted, their elbows flexed 90°, and their forearms in neutral, a methodology which is associated with high intra-test and inter-test reliability.94 Consistency in measuring
Conflict of interest statement
The authors have no disclosure of interest regarding this review article.
Acknowledgements
KN, NS and MP: concept, literature research and writing of the article. KN and MCG: concept of figures. MCG and JDS: critical revision. All authors have actively contributed, read and approved the final manuscript. No writing assistance was needed.
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