A non-ischemic forearm exercise test for the screening of patients with exercise intolerance

Abstract

The authors propose a standardized non-ischemic grip test that overcomes the main drawbacks of the classic ischemic forearm exercise test. It provides a specific, efficient, and safe screening test for patients with exercise intolerance. Its sensitivity was very good for patients with a glycogenolysis defect but remains partial in patients with a mitochondrial disorder.

Forearm Exercise Testing

“…An elevated baseline level of serum lactate may occur if • the forearm muscles are contracted while the baseline sample is taken. Mitochondrial disorders myopathies may be associated • with elevated baseline lactate [ 14 ] , as may numerous other toxic and metabolic disorders [ 5,23 ] . An elevated baseline serum ammonia level may be due to • medications such as valproic acid, smoking, and undue exertion prior to the test [ 24 ] .…”

“…Hogrel et al utilized isometric exercise for 30 s at 70 % of maximal voluntary contraction, without a sphygmomanometer cuff [ 5 ] . Although the authors describe their test as "nonischemic," this level of isometric contraction is probably suf fi cient to block blood fl ow [ 76 ] .…”

“…Forearm exercise test is relatively simple to perform and interpret and has proved to be a robust tool in diagnosing defects in muscle energy metabolism Exercise testing may be carried under conditions of ischemia or unrestricted blood fl ow. Reports of complications of the ischemia during forearm exercise testing in patients with glycogenoses have led some researchers to modify the test so that muscle ischemia is not intentionally produced [4][5][6] . Results of these modi fi ed forearm exercise tests have been similar to those of the ischemic forearm exercise testing.…”

Lactate production upon short-term non–ischemic forearm exercise in mitochondrial disorders and other myopathies

“…Lactate production during short-term exercise is not classically used for the detection of mitochondrial disorders. In patients with mitochondrial disorders the mean lactate curve of 14 patients fell into the normal range [3]. Three other studies using short-term high-intensity protocols which focused on the analysis of oxygen desaturation also reported no different exercise-induced venous peak lactate in patients with mitochondrial disorders, normal and diseased controls [7,9,10].…”

“…Three other studies using short-term high-intensity protocols which focused on the analysis of oxygen desaturation also reported no different exercise-induced venous peak lactate in patients with mitochondrial disorders, normal and diseased controls [7,9,10]. However, if the venous lactate was normalized to the mechanical energy production during exercise the sensitivity of the NIFET for mitochondriopathy was 57 % and the specifity for normal subjects and patients with unclassified exercise-induced complaints was 92 % [3]. Therefore, an increased lactate production normalized to the mechanical energy production (specific lactate production) was suggested as an early and specific indicator of disturbed oxidative phosphorylation in patients with mitochondrial disorders.…”