@article{BittmannDechSchaefer2023,
  author    = {Bittmann, Frank and Dech, Silas and Schaefer, Laura},
  title     = {Another way to confuse motor control},
  series = {Brain Sciences},
  volume    = {13},
  journal   = {Brain Sciences},
  number    = {7},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2076-3425},
  doi       = {10.3390/brainsci13071105},
  pages     = {20},
  year      = {2023},
  abstract  = {Sensorimotor control can be impaired by slacked muscle spindles. This was shown for reflex responses and, recently, also for muscular stability in the sense of Adaptive Force (AF). The slack in muscle spindles was generated by contracting the lengthened muscle followed by passive shortening. AF was suggested to specifically reflect sensorimotor control since it requires tension-length control in adaptation to an increasing load. This study investigated AF parameters in reaction to another, manually performed slack procedure in a preselected sample (n = 13). The AF of 11 elbow and 12 hip flexors was assessed by an objectified manual muscle test (MMT) using a handheld device. Maximal isometric AF was significantly reduced after manual spindle technique vs. regular MMT. Muscle lengthening started at 64.93 \& PLUSMN; 12.46\% of maximal voluntary isometric contraction (MVIC). During regular MMT, muscle length could be maintained stable until 92.53 \& PLUSMN; 10.12\% of MVIC. Hence, muscular stability measured by AF was impaired after spindle manipulation. Force oscillations arose at a significantly lower level for regular vs. spindle. This supports the assumption that they are a prerequisite for stable adaptation. Reduced muscular stability in reaction to slack procedures is considered physiological since sensory information is misled. It is proposed to use slack procedures to test the functionality of the neuromuscular system, which is relevant for clinical practice.},
  language  = {en}
}
@article{BittmannDechSchaefer2023,
  author    = {Bittmann, Frank and Dech, Silas and Schaefer, Laura},
  title     = {How to confuse motor control},
  series = {Life : open access journal},
  volume    = {13},
  journal   = {Life : open access journal},
  number    = {4},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2075-1729},
  doi       = {10.3390/life13040911},
  pages     = {18},
  year      = {2023},
  abstract  = {Adaptation to external forces relies on a well-functioning proprioceptive system including muscle spindle afferents. Muscle length and tension control in reaction to external forces is most important regarding the Adaptive Force (AF). This study investigated the effect of different procedures, which are assumed to influence the function of muscle spindles, on the AF. Elbow flexors of 12 healthy participants (n = 19 limbs) were assessed by an objectified manual muscle test (MMT) with different procedures: regular MMT, MMT after precontraction (self-estimated 20\% MVIC) in lengthened position with passive return to test position (CL), and MMT after CL with a second precontraction in test position (CL-CT). During regular MMTs, muscles maintained their length up to 99.7\% +/- 1.0\% of the maximal AF (AF(max)). After CL, muscles started to lengthen at 53.0\% +/- 22.5\% of AF(max). For CL-CT, muscles were again able to maintain the static position up to 98.3\% +/- 5.5\% of AF(max). AFiso(max) differed highly significantly between CL vs. CL-CT and regular MMT. CL was assumed to generate a slack of muscle spindles, which led to a substantial reduction of the holding capacity. This was immediately erased by a precontraction in the test position. The results substantiate that muscle spindle sensitivity seems to play an important role for neuromuscular functioning and musculoskeletal stability.},
  language  = {en}
}
@article{SchaeferCarnariusDechetal.2023,
  author    = {Schaefer, Laura and Carnarius, Friederike and Dech, Silas and Bittmann, Frank},
  title     = {Repeated measurements of Adaptive Force},
  series = {Frontiers in physiology},
  volume    = {14},
  journal   = {Frontiers in physiology},
  publisher = {Frontiers Research Foundation},
  address   = {Lausanne},
  issn      = {1664-042X},
  doi       = {10.3389/fphys.2023.1020954},
  pages     = {19},
  year      = {2023},
  abstract  = {The Adaptive Force (AF) reflects the neuromuscular capacity to adapt to external loads during holding muscle actions and is similar to motions in real life and sports. The maximal isometric AF (AFisoₘₐₓ) was considered to be the most relevant parameter and was assumed to have major importance regarding injury mechanisms and the development of musculoskeletal pain. The aim of this study was to investigate the behavior of different torque parameters over the course of 30 repeated maximal AF trials. In addition, maximal holding vs. maximal pushing isometric muscle actions were compared. A side consideration was the behavior of torques in the course of repeated AF actions when comparing strength and endurance athletes. The elbow flexors of n = 12 males (six strength/six endurance athletes, non-professionals) were measured 30 times (120 s rest) using a pneumatic device. Maximal voluntary isometric contraction (MVIC) was measured pre and post. MVIC, AFisoₘₐₓ, and AFₘₐₓ (maximal torque of one AF measurement) were evaluated regarding different considerations and statistical tests. AFₘₐₓ and AFisoₘₐₓ declined in the course of 30 trials [slope regression (mean ± standard deviation): AFₘₐₓ = -0.323 ± 0.263; AFisoₘₐₓ = -0.45 ± 0.45]. The decline from start to end amounted to -12.8\% ± 8.3\% (p < 0.001) for AFₘₐₓ and -25.41\% ± 26.40\% (p < 0.001) for AFisoₘₐₓ. AF parameters declined more in strength vs. endurance athletes. Thereby, strength athletes showed a rather stable decline for AFmax and a plateau formation for AFisoₘₐₓ after 15 trials. In contrast, endurance athletes reduced their AFₘₐₓ, especially after the first five trials, and remained on a rather similar level for AFisomax. The maximum of AFisoₘₐₓ of all 30 trials amounted 67.67\% ± 13.60\% of MVIC (p < 0.001, n = 12), supporting the hypothesis of two types of isometric muscle action (holding vs. pushing). The findings provided the first data on the behavior of torque parameters after repeated isometric-eccentric actions and revealed further insights into neuromuscular control strategies. Additionally, they highlight the importance of investigating AF parameters in athletes based on the different behaviors compared to MVIC. This is assumed to be especially relevant regarding injury mechanisms.},
  language  = {en}
}
@article{SchaeferBittmann2023,
  author    = {Schaefer, Laura and Bittmann, Frank},
  title     = {The adaptive force as a potential biomechanical parameter in the recovery process of patients with long COVID},
  series = {Diagnostics},
  volume    = {13},
  journal   = {Diagnostics},
  number    = {5},
  publisher = {MDPI},
  address   = {Basel},
  issn      = {2075-4418},
  doi       = {10.3390/diagnostics13050882},
  pages     = {25},
  year      = {2023},
  abstract  = {Long COVID patients show symptoms, such as fatigue, muscle weakness and pain. Adequate diagnostics are still lacking. Investigating muscle function might be a beneficial approach. The holding capacity (maximal isometric Adaptive Force; AFisomax) was previously suggested to be especially sensitive for impairments. This longitudinal, non-clinical study aimed to investigate the AF in long COVID patients and their recovery process. AF parameters of elbow and hip flexors were assessed in 17 patients at three time points (pre: long COVID state, post: immediately after first treatment, end: recovery) by an objectified manual muscle test. The tester applied an increasing force on the limb of the patient, who had to resist isometrically for as long as possible. The intensity of 13 common symptoms were queried. At pre, patients started to lengthen their muscles at ~50\% of the maximal AF (AFmax), which was then reached during eccentric motion, indicating unstable adaptation. At post and end, AFisomax increased significantly to ~99\% and 100\% of AFmax, respectively, reflecting stable adaptation. AFmax was statistically similar for all three time points. Symptom intensity decreased significantly from pre to end. The findings revealed a substantially impaired maximal holding capacity in long COVID patients, which returned to normal function with substantial health improvement. AFisomax might be a suitable sensitive functional parameter to assess long COVID patients and to support therapy process},
  language  = {en}
}