Assessment of muscle function

Isokinetic and isometric muscle strength were measured by using IsoMed 2000‐system B‐series version (D&R Ferstl GmbH, Hemau, Germany). The use of isokinetic dynamometer is considered a gold standard method to evaluate strength in cancer patients.2 It has already been shown to be valid and reliable in healthy subjects21 and has been used previously in various cancer populations.22, 23, 24

Maximal isokinetic peak torque (MIPT) was tested for shoulder external and internal rotation and for knee extensors and flexors at the angular velocities of 60 and 180°/s. The range of motion (ROM) for isokinetic knee measurement was limited between the angles from 10° to 90°. The position of the dynamometer for shoulder rotation was tilted at 40° of abduction. The ROM for isokinetic testing was from 10° external rotation to 70° internal rotation. The MIPT for shoulder rotation was calculated for dominant side.

With this device, we also measured the maximal voluntary isometric contraction (MVIC) for shoulder internal rotator in the position of 43° and knee extensor muscles in the position of 35° (0° is straight leg), which sustainably were the strongest angle positions. For BC patients, we calculated MVIC on the operated and non‐operated side. For healthy women, we calculated MVIC from the mean of left and right side.

Muscular fatigue was determined by the calculation of the peak torque decline at 60°/s in knee extensors of the dominant leg. Therefore, we used the muscular fatigue index: FI% = [(peak torque of initial three repetitions−peak torque of final three repetitions)/peak torque of initial three repetitions] × 100, an adapted formula as described by Kannus25 to define the ability of an individual to maintain a level of performance. A high FI% indicates that muscles fatigue quickly. The peak torque of the first repetition overall was markedly lower than that of the second repetition, and it was considered as a first ‘attempt’ for the patient; it was omitted from the calculation of the initial peak torque values.

Additionally, we measured the ROM in the arm elevation with a goniometer in a standardized supine lying position to elicit the flexibility limitations after surgery in both the operated and healthy sides.

Participants were secured using thigh, pelvic, and torso straps to minimize extraneous body movements. The subjects were permitted to use the handlebars on both sides of the IsoMed 2000 chair (D&R Ferstl GmbH, Hemau, Germany) for additional stability during leg testing, but not for shoulder testing. For the MVIC testing, the participants were instructed to push as hard as possible against the fixed lever arm. Contraction time for MVIC was restricted to 6 s for each position. Each subject performed 10 maximal reciprocal contractions in both angular velocities for MIPT. During testing, both the subject and the instructor were able to see the strength curve on the monitor. Subjects were given verbal encouragement to generate the highest possible strength. Each torque artefact resulting from deceleration, which often exceeds the true peak torque, was removed by using a filter; only gravity‐corrected data were used for analysis.