The Adaptive Force of Healthy Young Women Is Inuenced by Emotionally Affective Imaginations

Emotionally affective imaginations influence the Adaptive Force (AF) in healthy participants as 16 was recently shown. The AF describes the neuromuscular holding capacity, suggested to be 17 especially vulnerable for interfering inputs. The present study investigated the influence of 18 neutral, pleasant, and unpleasant food imaginations on the manually assessed AF objectified 19 by a handheld device of elbow and hip flexors in 12 healthy participants with improved design. 20 Muscle lengthening started on a significantly lower maximal isometric AF (AFiso max ) during 21 unpleasant vs. neutral and pleasant imaginations ( p < 0.001), whereby oscillations (AFosc) occurred mainly after AFiso max ( vs. 23 16%). Thus, healthy participants show an impaired holding function due to negative 24 imaginations. Assuming this leads to joint destabilization, musculoskeletal complaints might 25 result. It could support understanding the causal chain of linked pain and mental issues. A case 26 example (current stress vs. positive imaginations) will be presented, underpinning the hypothesis this approach might support psychomotor diagnostics and therapeutics.


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The mind-body connection has been discussed since decades. [1,2] It was postulated emotions 30 influence different body systems, like the autonomic, endocrine and motor systems. In case the previous findings will be positively verified, this would underpin the novel insights 76 into the interaction of emotions and motor control. Furthermore, it could serve as an 77 explanation for the still poorly understood pathomechanisms of musculoskeletal diseases 78 related to mental health issues. Perspectively, a positive verification might result in innovative 79 diagnostic approaches for mental but also particular physical health states. 80

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The study was performed in the Neuromechanics Laboratory of the University of Potsdam 82 (Germany). The AF of elbow and hip flexors of one side was investigated by the manual muscle 83 test (MMT) executed by one experienced female tester (35 years, 168 cm, 55 kg; 8 yrs. of 84 MMT experience) objectified by a handheld device regarding its reaction to emotionally 85 affective pleasant and unpleasant food imaginations and without imagination (neutral). In 86 addition to the tester, two assistants participated and conducted the measurements: the first 87 assistant was responsible for handling software, controlling the handheld device, and 88 protocolling, the second assistant guided the imagination.

90
A priori power analysis (G*Power 3.1.9.7) for group differences (dependent t-test, two-tailed) 91 on the base of the parameter with the lowest effect size of the previous study (unpleasant vs. 92 pleasant imagination; parameter , dz = 1.390)[9] revealed a necessary sample size of at 93 least n = 9 (α = 0.05, β = 0.95). In the anticipation of possible dropouts and due to an assumed 94 lower effect size because of the improved design with a presumably lower bias, n = 12 95 participants were measured. 96 A total of 12 healthy women volunteered to participate in the study (age: 24.92 ± 3.50 yrs.; 97 body mass: 64.08 ± 7.69 kg; body height: 170.67 ± 7.63 cm) (detailed information see 98 supplementary material Table S1). Inclusion criteria were female sex, age between 18 and 35 99 years and good overall health (values >0 on mood and physical wellbeing numeric analogue 100 scales from -8 (worst) to +8 (best)). The participants reported their mood on the measurement 101 day on that scale with 4.94 ± 1.73 and their physical well-being with 4.08 ± 1.17. Exclusion 102 criteria were current or previous (last six months) diseases or health complaints, current feeling 103 of stress and an ongoing or planned psychological treatment. Furthermore, an impaired 104 neuromuscular function of the tested muscles assessed by the MMT prior to the measurements 105 led to exclusion. 106 The study was conducted according to the guidelines of the Declaration of Helsinki and was 107 approved by the Ethics Committee of the University of Potsdam, Germany (protocol code Handheld device for Adaptive Force recordings 110 The reliable and valid handheld device ( Fig. 1a;  precision: 1.0 ± 0.1%, sensitivity: 0.3 mV/V) and kinematic sensor technology (Bosch BNO055, 114 9-axis absolute orientation sensor, sensitivity: ±1%) and records the reaction force, the 115 accelerations and angular velocity (gyrometry) between tester and participant during the MMT. 116 The sampling rate was 180 Hz. The data were buffered, AD converted and sent by Bluetooth shows the suggested optimal force profile applied externally by the tester during the MMT, which force rise is necessary at the beginning, so that the neuromuscular system of the participant 147 gets the chance to adapt to the rising force (for neurophysiological explanations see [28]). 148 Thirdly, a linear force increase follows. In case an oscillating force equilibrium between tester 149 and participant is reached, this should be sustained for a few seconds, whereby the maximal 150 AF (AFmax) is attained. The interaction is stopped by the tester and the force decreases again. 151 The duration of the entire force increase (phase 2 to 4) should be ~4 s (Fig. 1b) Two questionnaires had to be filled, the first one online prior to the measurement appointment. 160 It examined general data, current or planned psychological counselling, sensory perception of 161 food consumption while eating (e.g., odour, taste, optics, texture; scale from 1 = not important 162 to 5 = very important) as well as the three most pleasant and the three most unpleasant foods. 163 The foods had to be rated on a scale from -4 (most unpleasant) to +4 (most pleasant). Those 164 were the base for food imaginations during the MMT and were discussed at the measurement 165 appointment to get precise instructions for the imagination tasks (see below). Additionally, the 166 first questionnaire asked for preferences of food consumption (alone, in company, while 167 watching TV). 168 The second questionnaire was filled on-site before the measurements. The current state of 169 mood and physical well-being were obtained (see above). 170 171 The queried food preferences were discussed between participant, tester, and assistants on 172 the measurement day. The participant described the food experience as detailed as possible 173 and the tester noted the exact words used. Thereby, the tester enquired individual memorable 174 experiences of the two most pleasant and two most unpleasant foods as, e.g., smells, tastes, 175 associations etc. The aim was to identify triggering and exact words used by the participant to 176 ensure a well-executed imagination during the MMT trials. Furthermore, the participant chose 177 the most suitable picture of the respective food on a tablet (pictures of a common online search 178 engine) provoking pleasure or disgust. Across all participants, the most pleasant foods 179 included brownies, pasta with salmon, strawberries, chocolate, pancakes, mango, ice cream, 180 pizza, curry with rice, sushi, BLT sandwich, lasagne, potatoes with quark, mustard eggs, yeast 181 dumplings or hamburger; the most disgusting foods ranged from meat, fish, blood sausage, 182 beet root, octopus, offal, bananas, Brussels sprout, spinach, tomatoes on a sandwich, aspic, 183 liquorice to pickled gherkins. This highlights the very individual food choices perceived as 184 pleasant or unpleasant. Overall, the unpleasant foods were rated in 13 cases with -4, in 10 the participant who named "BLT Sandwiches" as one of her most pleasant foods (+4) described 188 it reminds her of the positive situation "being on family vacation in Sweden, sitting in the winter 189 garden and watching the lake" while "eating a BLT sandwich with fresh toast, mayonnaise, 190 lettuce, flavoursome bacon and tomatoes". She reported this as "experience of great pleasure". 191

Food imaginations
The same participant described her most unpleasant food (-4) as aspic. She described it as 192 "glibbery with pieces of meat inside, it wobbles in the mouth" and "you don´t know what is Prior to the measurement day, the participant received information on the study, the consent 214 paper, and the access to the first questionnaire via e-mail. On the measurement day, the tester 215 introduced the participant to the procedure and the informed declaration of consent was signed 216 before the second questionnaire was filled. In case mood and physical well-being were rated 217 on the scale with >0, the preliminary MMT of the elbow and hip flexors were executed on both 218 sides. In case of regular stability, the participant was included, and the muscles of her preferred 219 side were measured. If only one side showed regular stability, this side was used for the 220 following measurements. The measurement of Adaptive Force followed. In total, 18 trials were 221 performed: each two measurements of elbow and hip flexors without imagination (neutral; 222 'thinking of nothing particular', without picture) at the beginning; followed by 12 single-blinded, 223 randomized measurements: six tests during pleasant (tasty) and six during unpleasant 224 such as noises or sounds. As soon as the participant successfully imagined the respective 234 food (~20 s; indicated by head-nodding), the tester was informed to enter the laboratory. She 235 had no eye contact, neither to the participant (avoided by the curtain) nor to the assistants. The 236 first assistant named the muscle to be tested and confirmed that the handheld device was 237 ready for recording ("ok") without making eye-contact. Any further verbal interaction was 238 prohibited. The participant was priorly instructed to stay in her imagination during the MMT. 239 The whole procedure of one trial lasted ~40 s. Resting periods were ~60 s. After all pleasant 240 and unpleasant imagination trials, another neutral measurement with each muscle was 241 executed to check the status of muscular regulation after the imagination trials. After each trial, 242 the result of the subjective rating of the MMT (stable/unstable) was given by the tester to the 243 first assistant by a thumb up (stable) or thumb down (unstable) sign without eye contact. The 244 measurements were completed after the last neutral trial. 245 Afterwards, both muscles were tested again during each imagination without blinding, without 246 the curtain and without the handheld device. This should check the testers' evaluation of the 247 for feedback. Information on the imagination process or thoughts during the measurement 250 were of interest and were protocolled. 251 In the previous studies,[9,26] both interacting partners developed an oscillating force 303 equilibrium, especially in case of stable MMTs. This was accompanied by arising 304 oscillations in the force signal, indicating a clearly distinguishable regular oscillatory 305 behaviour (swing up). Therefore, the force at the moment of onsetting oscillations (AFosc 306 (N)) was investigated. For that, the force signal was checked for oscillations (force maxima) 307 appearing sequentially after the exponential phase (phase 2). In case, four force maxima 308 with a time distance dx < 0.15 s appeared consecutively, the force value of the first maxima 309 was defined as AFosc, which marked the force at the onset of oscillations. If no oscillations 310 appeared during the entire trial, AFosc = AFmax. For AFosc, the ratios to AFmax (%) and 311 maxAFmax (%) were calculated, too. It was previously found that AFosc appeared prior to 312

Data processing and statistical analysis
AFisomax in stable and after AFisomax in unstable MMTs, hence, the ratio (%) was 313 additionally calculated. 314  the result of at least one trial was not according to the hypothesis that during pleasant 368 imagination the AF would be stable; in two participants this was the case for 50% and 40% of 369 all imagination trials. Two other participants had difficulties to enter the imaginations. They also 370 showed deviations from the hypothesis in 17%. Only in two of the remaining 6 participants who 371 had no difficulties to imagine the food experience one trial each was not according to the 372 hypothesis. This might indicate that the trials which were not according to the hypothesis could 373 result from the imagination quality rather than from the tester's MMT performance. 374 In contrast, the gyrometer signals during neutral (grey) and pleasant (blue) imaginations 387 oscillate around zero throughout the entire force increase, reflecting the quasi-isometric muscle  413 The slope of force rises for elbow and hip flexors revealed no significant difference between 414 the three groups (elbow: χ²(2) = 0.722, p = 0.697, n = 10; hip: χ²(2) = 0.250, p = 0.882, n = 8, 415  422 For elbow flexors the AFmax showed no significant difference between the three groups 423 (F(2,18) = 1.427, p = 0.266), reflecting that the AFmax, irrespective if reached during isometric 424 or eccentric muscle action, was similar between the imaginations (Fig. 5a, Table 1   During neutral and pleasant imaginations was 100 ± 0% and 97.14 ± 5.00% for elbow 453 flexors, respectively, and 98.54 ± 3.55% and 95.22 ± 6.66% for hip flexors, respectively (Table  454 1, Fig. 5c,f) (Table 1, S8). Furthermoreand in contrast to elbow flexors -AFosc 500 was significantly lower for neutral state vs. pleasant imaginations (Fig. 6d). The ratio 501 amounted 66.17 ± 14.08%, 76.27 ± 17.50% and 161.17 ± 130.54% during neutral, pleasant, 502 and unpleasant imaginations, respectively. This reflects the high variation of the oscillatory 503 onset related to the breaking point for unpleasant imaginations, which is visible in the 95%-CIs 504 (Fig. 6f). In 6 of 11 participants, the oscillations occurred after the breaking point (AFisomax) during unpleasant imaginations (105.8 % to 521.3 %), however, in 5 of 11 participants, the 506 oscillations arose before the breaking point (83.7 % to 94.7 %). 507

508
The present study should verify previous findings regarding the influence of pleasant and 509 unpleasant emotionally affective imaginations on different AF parameters of elbow and hip 510 flexors in an improved design. Since the force rises (slope) did not differ significantly between 511 neutral state, pleasant and unpleasant imaginations, the following considerations are based 512 on reproducible force rises. 513 At first it should be stated that the blinding did not lead to a considerably different MMT 514 assessment by the tester compared to non-blinding, which was the main limitation of the 515 previous study. It was hypothesized the MMTs would be rated as stable for neutral and 516 pleasant and as unstable for unpleasant imaginations. For elbow flexors, this was the case in 517 100% for neutral state and ~90% for pleasant as well as for unpleasant imaginations; for hip 518 flexors, 97%, 87% and 84%, respectively, were assessed according to the hypothesis, 519 whereby for unpleasant imaginations, 9% of the MMTs were classified as unclear. Thus, even 520 though the tester did not know which imagination was performed, the subjective rating of the 521 MMTs showed the effect of reduced stability for unpleasant imaginations. Some limitations 522 (above-mentioned) must be considered regarding imagination quality which possibly led to the 523 deviating results. 524 The main hypothesis (1)  Although the present study design was improved compared to the previous, including single-557 blinding and randomization, limitations especially regarding the evaluation must be considered. 558 The evaluation of the oscillatory onset (AFosc) was adopted from the previous study and is 559 based on the criterion that four consecutive maxima in force rise with a time distance dx < 0.15 560 s must arise. The amplitude and frequency of those oscillations were not considered. As above-561 mentioned, in some cases a clear swing up was missing, although four consecutive maxima 562 were present. Therefore, the algorithm of oscillatory onset should be revised. From a visual 563 inspection, the frequency and the amplitude seem to differ between stable and unstable MMTs. 564 Therefore, probably a power-frequency analysis could be applied. 565 Furthermore, the quality of imagination was not assessed quantitatively. The talk after the 566 measurements gave an impression on how good the participant interpreted their ability to 567 mentioned. This might have led to deviations regarding the stability of AF. However, the aim 569 was not to quantify the quality of imagination but their general effect on AF. Therefore, they 570 were included. 571 Possible limitations concerning MMT performance were previously described,[9,26] especially 572 regarding the maximal value and slope of force application. The hip flexors showed a 573 significantly lower AFmax for trials without imagination (discussed above). This might result 574 from the lower maximal force applied by the tester, probably because of perceiving the mutual 575 oscillations already on a low force level. Since the crucial parameter is the AF under isometric 576 conditions (AFisomax), which was still clearly and significantly lower during unpleasant 577 imagination, the lower AFmax in neutral state can be neglected here. 578 on muscular activity in healthy participants. [10,18,19] It is suggested that the AF, especially 588 the isometric AF, characterizes a particular functioning of the neuromuscular control which 589 seems to be highly sensitive to interfering inputs. Because not only emotional states are 590 intervening motor processing but also various afferences like nociception or proprioception, it 591 is suggested that the AF could be influenced by other disturbing factors. Based on the findings, 592 negative imaginations apparently result in substantial muscular instability even in healthy 593 participants. It can only be assumed how stressful situations and traumas influence the AF. If 594 stress is persisting (at work, relationships, conditions after traumatic experiences, e.g., 595

Neurophysiological considerations of muscular adaptations and practical
accidents, death of related persons or alike), we expect an impaired holding function in the 596 sense of AFisomax. This is based on own experience of long-term clinical practice and is 597 supported by the present findings. If the holding function is impaired permanently, joints might 598 not be stabilized appropriately anymore. In daily activities and sports, the adaptive muscular 599 capability is necessary for joint stabilization. In case the holding capacity is reduced, joints 600 could suffer from inappropriate joint alignment under strain, which might result in pain and 601 probably leads to degeneration or increased danger of injury. This could explain the still poorly 602 understood "overuse"-injuries and might clarify the causal chain regarding the above-603 mentioned pain associated with mental health. From our point of view, mental problems lead 604 to an impaired neuromuscular control which, in turn, could result in complaints of the 605 musculoskeletal system. The results of the present investigation underpin this hypothesis, 606 since already healthy participant showed a reduced muscular holding capacity even by just 607 imagining unpleasant food experiences. This effect was only temporary and could be reversed 608 immediately by imagining pleasant experiences. It is assumed that for persons suffering from chronic stress the AF might be impaired permanently. In those cases, a positive effect could 610 be gained by, e.g., imagining positive situations. 611 Case example: Adaptive Force under current stress vs. positive imaginations 612 One female participant (28 years, 174 cm, 69 kg) initially showed an impaired neuromuscular 613 function in preliminary MMTs. A brief talk revealed she experienced current stress (time 614 pressure, several exams ahead). The initial instability of her muscles could be repealed by 615 positive imaginations (yoga or victory in kickboxing competition; both good feelings of 616 relaxation and strength). Therefore, we decided spontaneously to perform the AF 617 measurements of elbow and hip flexors (same setting as above) using the negative imagination 618 (exam situation) vs. the positive imaginations (yoga/kickboxing) randomized and single-blinded 619 (each 3x per muscle). After this, one measurement without imagination was finally performed 620 for both muscles. For negative imaginations, the elbow flexors showed an unstable behaviour 621 in 2 of 3 trials, in one trial the MMT was rated as stable despite of negative imagination. For 622 positive imaginations, the elbow flexors were rated as stable for all trials. For hip flexors, all 623 three trials during negative imagination were unstable, for positive imagination, the first two 624 trials were assessed as stable and the last one as unstable. Also, the subsequent neutral trial 625 of hip flexors was unstable, whereas the neutral trial for elbow flexors was stable. Figure 7  626 displays exemplary measuring curves of force and gyrometer signals for elbow and hip flexors 627 during positive (blue) and negative imaginations (red). The tester's MMT ratings were again 628 confirmed by the recorded data of the handheld device.
was 49 ± 5% 631 and 189 ± 177% for positive and negative imaginations for elbow flexors, respectively, and 93 632 ± 61 % and 201 ± 25 % for hip flexors, respectively. The AFisomax was considerably lower 633 during negative imaginations, which was the entry state of the participant. By imagining positive 634 experiences, the holding capability was immediately improved, indicating a regular 635 neuromuscular function. The oscillatory onset in stable MMTs occurred before and for unstable 636 MMTs after AFisomax. 637 This case example indicates that emotional stress might lead to a persisting state of muscular 638 instability. In such cases, positive imaginations might help to resolve this impaired condition. 639 Hence, the AF assessment seems to be suitable to evaluate this effect and to test which 640 proposed. Including the findings of this study, the suggested values can be extended. In the 653 following, the data of all three studies are included. Stable adaptation seems to be 654 characterized by a high AFisomax ≈ AFmax (≥ 99% of AFmax), indicating the muscle length 655 stays quasi-isometric during the entire force increase. Unstable adaptation, in turn, shows a 656 significantly lower AFisomax ≈ 56% of AFmax, reflecting that the muscle starts to lengthen on a 657 significantly lower force during adaptation. Furthermore, during stable adaptation oscillations 658 occur at a force level ~73% of AFmax, in turn, for unstable adaptation at ~88%. The occurrence 659 of oscillations for unstable adaptation was on a higher force level based on previous data and 660 for elbow flexors here (~95%). It is not clear, why the oscillations under unstable conditions for 661 hip flexors arose on a low force level in the present study (75%). Hereby, as above-mentioned, 662 the evaluation might play a role or possibly the participant's regulatory state. However, it seems 663 to be more important if oscillations arise before or after AFisomax ( ). Considering the 664 data of all three studies, 202 stable and 124 unstable MMTs were recorded. In 197 stable trials 665 (97.5%), oscillations occurred before AFisomax, thus, in isometric conditions; in 108 unstable