T/A-analysis with or without measuring force: problems in the evaluation of normal limits

Turn/amplitude-analysis (TAA) has been applied to interference patterns of the right m. biceps brachii and the right m. rectus femoris of 33 healthy women aged 19 to 53 years. Interference patterns were recorded at 20, 40 and 60% +/- 10% of both muscles maximum force. The dependency of the turn/amplitude-parameters (T/A-parameters) on age, muscle and force is discussed. Normal limits for individual means of the T/A-parameters were calculated in form of the +/- 2 SD. Normal limits for single values were calculated in form of clouds. Both methods were applied to the values of each force level (20, 40 and 60%) and of all force levels together (10-70%). Clouds of the present study were clearly different from those of Stålberg. Evaluating individual means rates of false positive results were higher compared to those of single values. Rates of false positive results for single values and individual means of the parameters T/S and A/T were lower at the 20% force level than at the higher force levels and without measuring force. For the application of the TAA we advise every electrophysiological laboratory 1) to evaluate single values instead of individual means, 2) to use clouds instead of the +/- 2 SD as normal limits, 3) to measure force until a modified cloud-method will be applicable and 4) to elaborate its own normal limits.