Use of inertial measurement units to assess movement and performance

The ability to generate muscle power, defined as the product of force and velocity, is considered one of the major responsible of falls, injuries, and functional limitations. To evaluate functional ability, in particular muscle power, motor capacity and motor development, several field tests such as Countermovement jump (CMJ) and Squat Jump (SJ) are considered as the most accurate tests to evaluate lower limbs skills. These measurements are typically carried out through the use of force plates, defined as the “gold standard” for their accuracy, and subsequently, information is extrapolated through equations. However, Inertial Measurement Units (IMUs) are promising alternatives to laboratory-based motion capture methods in biomechanical assessment of athletic movements and overcome the force platforms’ costs and transportability issues. For upper limb assessment, IMUs, in combination with tools like the wobble board (WB), enable the analysis of fine motor skills and inter-limb asymmetry, especially useful for evaluating hand stability, coordination, and tremor control. These applications are essential for capturing complex aspects of upper limb motor control, such as the effects of hand exercises on tremor asymmetry and overall fine motor skills, which are pivotal in tasks requiring precise and coordinated movements. For these reasons, the main aim of this thesis was to explore the use of IMU to assess the acute effects of targeted training sessions on upper and lower limb performance, with specific focus on enhancing motor control, reducing inter-limb asymmetries, and optimizing biomechanical and neuromuscular responses in healthy subjects. Building on this overarching aim, research has been organized into three principal distinct areas of investigation as follows: (a) to evaluate the acute effects of mini trampoline training on lower limb Stiffness and Reactive Power and its immediate impact on training, contributing to the development of evidence-based training protocols; (b) to evaluate intra-limb asymmetry using a WB following mini trampoline training by exploring the characteristics of asymmetry within the lower limbs, and (c) to evaluate the acute effects of WB hand exercise training on the inter-limb asymmetry of tremors. Methods The project is organized into three distinct phases: I. the first part of the present project aimed to evaluate the sex-related acute effects of a single mini trampoline training session on leg Stiffness (K) and Reactive Power (RP) in young adults. Twenty college students (11 females, 9 males) participated in the study. After a familiarization jumping session, the subjects performed a repetitive jump test to assess lower limb stiffness and muscle RP before (PRE) and after (POST) the Superjump® training session. The Superjump® training session consisted of a period of free practice on the mini trampoline followed by a 30-min workout, during which subjects were required to engage in continuous jumping and perform upper limb exercises and breathing exercises. II. The leg stiffness mean (KMEAN) and RP mean of the five repetitive jumps (RJs) in each of the three trials along with the mean of the best RJs (one per trial) (KBEST) over the five jumps for each subject were considered for the subsequent analysis. III. Despite the beneficial acute and chronic effects of mini trampoline training on several physical outcomes, no study has yet investigated its acute effects on dynamic balance performances and balance inter-limb asymmetries in young subjects. For this purpose, the second part of this project evaluated the acute effects of Superjump® training on dynamic balance performance and Bilateral Asymmetry (BA) and Unilateral Asymmetry (UA) Indexes in healthy young adults. Following a familiarization session, participants completed a 30-minute mini trampoline workout, focusing on different hopping exercises involving both lower and upper limbs. Dynamic balance was assessed using a WB test, where subjects performed single-leg stance trials to minimize motion marker (MM) displacement. Bilateral and unilateral asymmetry (UA and BA) indices were calculated. IV. Regarding the third part, since eye–hand coordination has a significant impact on sporting performance and daily activities, it was investigated the impact on hand tremors and inter-limb asymmetry. Therefore, the main aim of the study was to evaluate the effect of eye–hand coordination exercises on the asymmetry of physiological hand tremor in healthy young participants, in relation to sex. A total of 38 apparently healthy young participants were evaluated using a tri-axial accelerometer (TalentPlayers TPDev, firmware version 1.3) to measure the postural hand tremor. Hand tremor magnitude was recorded for both dominant and non-dominant limbs before (PRE) and after (POST) WB hand exercises. The goal was to evaluate the impact of hand-eye coordination exercises on hand tremor asymmetry. Participants Participants were selected among the student population of the University of Cassino and Lazio Meridionale. Only participants aged between 20 and 35 years old were selected. Participants were also excluded if they reported pre- existing diagnosed conditions such as neurological conditions, cardiovascular, respiratory, and/or metabolic diseases, hypertension, osteoporosis, musculoskeletal injury of the back or lower extremities that had occurred during the past year, visual and vestibular disorders, or any drugs use. The project was conducted following the guidelines of the Declaration of Helsinki and received approval from the Institutional Review Board of the Department of Human Science, Society, and Health of the University of Cassino and Lazio Meridionale. Prior to participating, all participants read and signed a written consent form, and they were informed of their right to withdraw from the study at any time without facing any consequences. In accordance with the Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016, also known as the General Data Protection Regulation (GDPR), which safeguards the rights and privacy of individuals with respect to the processing of personal data, we took measures to ensure the appropriate security and confidentiality of the participants’ personal data. To maintain anonymity, each participant was assigned a unique identification code, and their personal data were solely used for statistical purposes. Results The main findings from this project include the following: Phase I: Women exhibited significantly lower KMEAN and KBEST values than men both before (PRE) and after (POST) the mini trampoline training session, with these sex differences persisting post-training. Both men and women showed significant improvements in RP after the training session. Phase II: SJ training significantly reduced UA in lower limb balance, as indicated by the UA index. Subjects with higher baseline UA showed greater improvements following the SJ intervention. There was no significant effect of SJ training on BA, though dynamic balance performance on the WB improved in both men and women post-training. Phase III: Hand-eye coordination exercises led to a significant reduction in inter-limb asymmetry of hand tremors. This effect was observed across both sexes, with tremor asymmetry present PRE intervention and disappearing POST intervention. Collectively, these studies illustrate the effectiveness of IMU-based assessments and specific training interventions in improving motor control, stability, and symmetry, thus supporting their application in sports and clinical settings. Conclusions The findings highlight the potential of targeted training interventions using mini trampolines and WBs, in enhancing motor performance and balance. Specifically, the first study demonstrated that Superjump® training effectively increased lower limb K and RP, suggesting it as a valuable tool for improving muscular response in athletic training. The second study revealed that mini trampoline exercises could significantly reduce intra-limb asymmetry in dynamic balance, underlining its role in promoting musculoskeletal equilibrium and injury prevention. Lastly, the third study showed that WB hand exercises effectively decreased inter-limb asymmetry in physiological hand tremors, illustrating their utility in improving fine motor control and hand stability. Collectively, these results emphasize the practicality of IMU-based assessments and targeted training protocols to foster balanced motor function and support both clinical and athletic applications.