SUMMARY Tendons are able to remodel their mechanical and morphological properties in response to mechanical loading. However, there is little information about the effects of controlled modulation in cyclic strain magnitude applied to the tendon on the adaptation of tendon's properties in vivo. The present study investigated whether the magnitude of the mechanical load induced as cyclic strain applied to the Achilles tendon may have a threshold in order to trigger adaptation effects on tendon mechanical and morphological properties. Twenty-one adults (experimental group, N=11; control group, N=10) participated in the study. The participants of the experimental group exercised one leg at low-magnitude tendon strain (2.85±0.99%) and the other leg at high-magnitude tendon strain (4.55±1.38%) of similar frequency and volume. After 14 weeks of exercise intervention we found a decrease in strain at a given tendon force, an increase in tendon-aponeurosis stiffness and tendon elastic modulus and a region-specific hypertrophy of the Achilles tendon only in the leg exercised at high strain magnitude. These findings provide evidence of the existence of a threshold or set-point at the applied strain magnitude at which the transduction of the mechanical stimulus may influence the tensional homeostasis of the tendons. The results further show that the mechanical load exerted on the Achilles tendon during the low-strain-magnitude exercise is not a sufficient stimulus for triggering further adaptation effects on the Achilles tendon than the stimulus provided by the mechanical load applied during daily activities.

The need to move over uneven terrain is a daily challenge. In order to face unexpected perturbations due to changes in the morphology of the terrain, the central nervous system must flexibly modify its control strategies. We analysed the local dynamic stability and the modular organisation of muscle activation (muscle synergies) during walking and running on an even- and an uneven-surface treadmill. We hypothesized a reduced stability during uneven-surface locomotion and a reorganisation of the modular control. We found a decreased stability when switching from even- to uneven-surface locomotion (p < 0.001 in walking, p = 0.001 in running). Moreover, we observed a substantial modification of the time-dependent muscle activation patterns (motor primitives) despite a general conservation of the time-independent coefficients (motor modules). The motor primitives were considerably wider in the uneven-surface condition. Specifically, the widening was significant in both the early (+40.5%, p < 0.001) and late swing (+7.7%, p = 0.040) phase in walking and in the weight acceptance (+13.6%, p = 0.006) and propulsion (+6.0%, p = 0.041) phase in running. This widening highlighted an increased motor output’s robustness (i.e. ability to cope with errors) when dealing with the unexpected perturbations. Our results confirmed the hypothesis that humans adjust their motor control strategies’ timing to deal with unsteady locomotion.

BackgroundPreference-based tempo-pace synchronized music has been shown to reduce perceived physical activity exertion and improve exercise performance. The extent to which such strategies can improve adherence to physical activity remains unknown. The objective of the study is to explore the feasibility and efficacy of tempo-pace synchronized preference-based music audio-playlists on adherence to physical activity among cardiovascular disease patients participating in a cardiac rehabilitation.MethodsThirty-four cardiac rehabilitation patients were randomly allocated to one of two strategies: (1) no music usual-care control and (2) tempo-pace synchronized audio-devices with personalized music playlists + usual-care. All songs uploaded onto audio-playlist devices took into account patient personal music genre and artist preferences. However, actual song selection was restricted to music whose tempos approximated patients’ prescribed exercise walking/running pace (steps per minute) to achieve tempo-pace synchrony. Patients allocated to audio-music playlists underwent further randomization in which half of the patients received songs that were sonically enhanced with rhythmic auditory stimulation (RAS) to accentuate tempo-pace synchrony, whereas the other half did not. RAS was achieved through blinded rhythmic sonic-enhancements undertaken manually to songs within individuals’ music playlists. The primary outcome consisted of the weekly volume of physical activity undertaken over 3 months as determined by tri-axial accelerometers. Statistical methods employed an intention to treat and repeated-measures design.ResultsPatients randomized to personalized audio-playlists with tempo-pace synchrony achieved higher weekly volumes of physical activity than did their non-music usual-care comparators (475.6 min vs. 370.2 min, P < 0.001). Improvements in weekly physical activity volumes among audio-playlist recipients were driven by those randomized to the RAS group which attained weekly exercise volumes that were nearly twofold greater than either of the two other groups (average weekly minutes of physical activity of 631.3 min vs. 320 min vs. 370.2 min, personalized audio-playlists with RAS vs. personalized audio-playlists without RAS vs. non-music usual-care controls, respectively, P < 0.001). Patients randomized to music with RAS utilized their audio-playlist devices more frequently than did non-RAS music counterparts (P < 0.001).ConclusionsThe use of tempo-pace synchronized preference-based audio-playlists was feasibly implemented into a structured exercise program and efficacious in improving adherence to physical activity beyond the evidence-based non-music usual standard of care. Larger clinical trials are required to validate these findings.Trial registrationClinicalTrials.gov ID (NCT01752595)Electronic supplementary materialThe online version of this article (doi:10.1186/s40798-015-0017-9) contains supplementary material, which is available to authorized users.

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