Human Performance

Endurance type exercise

To asses the maximal endurance capacity of our subjects, we generally use an incremental cycling exercise test to exhaustion. The subject cycles on an electronically braked cycle ergometer (Lode Excalibur, Groningen, The Netherlands), while his oxygen consumption and carbon dioxide production is measured by indirect calorimetry (Oxycon Pro, Mijnhart). During the test, the respiratory exchange ratio (RER), VO2, VCO2, heart rate, workload and cycling cadence are recorded. The protocol usually consists of a 5 min warm-up period, after which the workload is set at 75 W for women and 100 W for men. Every 2.5 min, the load is increased by 25-50 W until exhaustion. We generally use this maximal cycling test for screening purposes. An adapted protocol is being used for deconditioned patients.

To investigate the effect of an intervention on exercise performance, we use a specific time trial protocol. This protocol shows a coefficient of variation of ~3%. In a pretest, subject’s maximal workload capacity will be determined as described above. The target amount of work for the time trial is based on maximal workload capacity. It is assumed that a subject can cycle for 1 h at 75% Wmax. Target amount of work (J) is set at: 0.75 x Wmax x 3600 (sec). To simulate a field setting, the ergometer is set in a linear setting, with the linear factor set according to subject’s preferred cycling cadence. During the time trial, subjects only receive information on the percentage of the total preset work that has already been performed. No information is given on workload, pedaling rate, heartrate and time.



Other peformance tests include submaximal endurance trials to exhaustion and submaximal tests in which endogenous and/or exogenous substrate utilization rates are being used as markers for optimal performance. In the latter experiments indirect calorimetry, stable isotopes, blood and/or muscle sampling are generally applied.


Resistance type exercise
For determining muscle strength, 2 different assessment methods are generally applied in research and clinical practice: dynamometry and 1RM testing. Both methods are available within our Department. For dynamometry, we are routinely using a Cybex-II dynamometer, which enables us to assess both isometric and isokinetic (concentric) muscle strength. Though the Cybex is generally being used for determining knee extension and flexion strength, the machine can be adapted for assessing muscle strength around any desired joint, e.g., ankle, hip, shoulder, and/or elbow.



One repetition maximum-, or 1RM-testing refers to the assessment of the maximum amount of weight that can be lifted in a specific exercise. The latter can be done on both standard weightlifting (resistance training) equipment and/or using free weights. The equipment in our lab allows us to perform 1RM testing on various muscle groups of the upper and lower extremity, by using machines for leg press, leg extension, chest press, biceps curl, etc. The standard procedure being used includes at least one familiarization trial in which the exercise is explained and proper lifting technique is being demonstrated and practiced. In a second trial, 1RM is usually determined by performing a proper lift once, and then repeating the procedure with gradually increasing the weight that is lifted. This is done until proper execution of the exercise is no longer possible. 1RM is defined as the maximum amount of weight that can be lifted with proper execution, and should preferably be determined within 4-5 attempts to prevent fatigue.