Time-dependent cortical plasticity during moderate-intensity continuous training versus high-intensity interval training in rats.

The temporal pattern of cortical plasticity induced by high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) is required to clarify their relative benefits to prevent neurological disorders. The purpose of this study is to define the time-dependent effects of work-matched HIIT and MICT on cortical plasticity, endurance, and sensorimotor performances over an 8-week training period in healthy rats. Adult healthy rats performed incremental exercise tests and sensorimotor tests before and at 2, 4, and 8 weeks of training. In parallel, cortical markers related to neurotrophic, angiogenic, and metabolic activities were assessed. Results indicate that HIIT induced an early and superior endurance improvement compared to MICT. We found significant enhancement of speed associated with lactate threshold (SLT) and maximal speed (Smax) in HIIT animals. MICT promoted an early increase in brain-derived neurotrophic factor and angiogenic/metabolic markers but showed less influence at 8 weeks. HIIT upregulated the insulin-like growth factor-1 (IGF-1) as well as neurotrophic, metabolic/angiogenic markers at 2 and 8 weeks and downregulated the neuronal K-Cl cotransporter KCC2 that regulates GABAA-mediated transmission. HIIT and MICT are effective in a time-dependent manner suggesting a complementary effect that might be useful in physical exercise guidelines for maintaining brain health.

Effects of Different High-Intensity Interval Training Regimens on Endurance and Neuroplasticity After Cerebral Ischemia.

BACKGROUND AND PURPOSE: The objective is to compare the effects of high-intensity interval training (HIIT) with long versus short intervals on endurance and motor performance. Their influence on neuroplasticity markers is assessed in the ipsilesional and contralesional cortex and hippocampus since their remodeling could improve functional recovery. METHODS: Rats performed work-matched HIIT4 (long intervals: 4 minutes) or HIIT1 (short intervals: 1 minute) on treadmill for 2 weeks following transient middle cerebral artery occlusion. Forelimb grip strength evaluated motor function while incremental exercise tests measured the endurance performance. Key neuroplasticity markers were assessed by Western blot. RESULTS: Both regimens were effective in enhancing both the speed associated with the lactate threshold and maximal speed at D8 and D15. Neuroplasticity markers were upregulated in the contralesional hemisphere after training contrary to the ipsilesional side. Grip strength completely recovered but is faster with HIIT4. CONCLUSIONS: HIIT with short and long intervals induced early aerobic fitness and grip strength improvements. Our findings revealed that neuroplasticity markers were upregulated in the contralesional cortex and hippocampus to promote functional recovery.

Is High-Intensity Interval Training Suitable to Promote Neuroplasticity and Cognitive Functions after Stroke?

Stroke-induced cognitive impairments affect the long-term quality of life. High-intensity interval training (HIIT) is now considered a promising strategy to enhance cognitive functions. This review is designed to examine the role of HIIT in promoting neuroplasticity processes and/or cognitive functions after stroke. The various methodological limitations related to the clinical relevance of studies on the exercise recommendations in individuals with stroke are first discussed. Then, the relevance of HIIT in improving neurotrophic factors expression, neurogenesis and synaptic plasticity is debated in both stroke and healthy individuals (humans and rodents). Moreover, HIIT may have a preventive role on stroke severity, as found in rodents. The potential role of HIIT in stroke rehabilitation is reinforced by findings showing its powerful neurogenic effect that might potentiate cognitive benefits induced by cognitive tasks. In addition, the clinical role of neuroplasticity observed in each hemisphere needs to be clarified by coupling more frequently to cellular/molecular measurements and behavioral testing.

Does an increase in energy return and/or longitudinal bending stiffness shoe features reduce the energetic cost of running?

PURPOSE: This study focused on the effects of shoe energy return and shoe longitudinal bending stiffness on the energetic cost and biomechanics of running. METHODS: The energetic cost of running and biomechanical variables altering running economy (ground contact times, stride frequency, vertical and leg stiffness, ground reaction force impulses, alignment between the resultant ground reaction force and the leg) were measured for nineteen male recreational runners. Participants ran overground under their ventilatory anaerobic threshold (10.8 ± 1.1 km h-1 on average) using four shoe prototypes with features combining low or high magnitudes of energy return and longitudinal bending stiffness. RESULTS: Neither the energy return, nor the longitudinal bending stiffness, or the interaction of these shoe features altered the energetic cost of running. High energy return shoes induced significant increased ground contact time from 274.5 ± 18.3 to 277.1 ± 18.7 ms, and significant decreased stride frequency from 1.34 ± 0.05 to 1.33 ± 0.05 Hz. High bending stiffness shoes induced significant increased ground contact time from 273.8 ± 18.2 to 277.9 ± 18.7 ms, significant increased vertical stiffness from 23.2 ± 3.4 to 23.8 ± 3.0 kN m-1, and significant decreased net vertical impulse from 245.4 ± 17.2 to 241.7 ± 17.5 BW ms. CONCLUSIONS: Increased energy return and longitudinal bending stiffness induced subtle changes in the running biomechanics, but did not induce any decrease in the energetic cost of running.

Performing pull-ups with small climbing holds influences grip and biomechanical arm action.

Pull-ups are often used by sport-climbers and other athletes to train their arm and back muscle capabilities. Sport-climbers use different types of holds to reinforce finger strength concomitantly. However, the effect of grip types on pull-up performance had not previously been investigated. A vertical force platform sensor measured the force exerted by climbers when performing pull-ups under six different grip conditions (gym-bar, large climbing hold, and four small climbing holds: 22mm, 18mm, 14mm, and 10mm). The electromyography of finger flexors and extensor muscles were recorded simultaneously. The maximal arm power and summed mechanical work were computed. The results revealed that the number of pull-ups, maximal power, and summed mechanical work decreased significantly with the size of the climbing hold used, even if no differences were found between a large climbing hold and a gym-bar. Electromyography of the forearm muscles revealed that the use of a climbing hold generated finger flexor fatigue and that the level of cocontraction was impacted by the different segment coordination strategies generated during the pull-ups. These findings are likely to be useful for quantifying training loads more accurately and designing training exercises and programs.

Impaired corticomuscular coherence during isometric elbow flexion contractions in humans with cervical spinal cord injury.

After spinal cord injury (SCI), the reorganization of the neuromuscular system leads to increased antagonist muscles' co-activation-that is, increased antagonist vs. agonist muscles activation ratio-during voluntary contractions. Increased muscle co-activation is supposed to result from reduced cortical influences on spinal mechanisms inhibiting antagonist muscles. The assessment of the residual interactions between cortical and muscles activity with corticomuscular coherence (CMC) in participants with SCI producing different force levels may shed new lights on the regulation of muscle co-activation. To achieve this aim, we compared the net joint torque, the muscle co-activation and the CMC ~ 10 and ~ 20 Hz with both agonist and antagonist muscles in participants with SCI and healthy participants performing actual isometric elbow flexion contractions at three force levels. For all participants, overall CMC and muscle co-activation decreased with the increase in the net joint torque, but only CMC ~ 10 Hz was correlated with muscle co-activation. Participants with SCI had greater muscle co-activation and lower CMC ~ 10 Hz, at the highest force levels. These results emphasize the importance of CMC as a mechanism that could take part in the modulation of muscle co-activation to maintain a specific force level. Lower CMC ~ 10 Hz in SCI participants may reflect the decreased cortical influence on spinal mechanisms, leading to increased muscle co-activation, although plasticity of the corticomuscular coupling seems to be preserved after SCI to modulate the force level. Clinically, the CMC may efficiently evaluate the residual integrity of the neuromuscular system after SCI and the effects of rehabilitation.

Effects of hand configuration on muscle force coordination, co-contraction and concomitant intermuscular coupling during maximal isometric flexion of the fingers.

PURPOSE: The mechanisms governing the control of musculoskeletal redundancy remain to be fully understood. The hand is highly redundant, and shows different functional role of extensors according to its configuration for a same functional task of finger flexion. Through intermuscular coherence analysis combined with hand musculoskeletal modelling during maximal isometric hand contractions, our aim was to better understand the neural mechanisms underlying the control of muscle force coordination and agonist-antagonist co-contraction. METHODS: Thirteen participants performed maximal isometric flexions of the fingers in two configurations: power grip (Power) and finger-pressing on a surface (Press). Hand kinematics and force/moment measurements were used as inputs in a musculoskeletal model of the hand to determine muscular tensions and co-contraction. EMG-EMG coherence analysis was performed between wrist and finger flexors and extensor muscle pairs in alpha, beta and gamma frequency bands. RESULTS: Concomitantly with tailored muscle force coordination and increased co-contraction between Press and Power (mean difference: 48.08%; p < 0.05), our results showed muscle-pair-specific modulation of intermuscular coupling, characterized by pair-specific modulation of EMG-EMG coherence between Power and Press (p < 0.05), and a negative linear association between co-contraction and intermuscular coupling for the ECR/FCR agonist-antagonist muscle pair (r = - 0.65; p < 0.05). CONCLUSIONS: This study brings new evidence that pair-specific modulation of EMG-EMG coherence is related to modulation of muscle force coordination during hand contractions. Our results highlight the functional importance of intermuscular coupling as a mechanism contributing to the control of muscle force synergies and agonist-antagonist co-contraction.

Active tuning of stroke-induced vibrations by tennis players.

This paper investigates how tennis players control stroke-induced vibration. Its aim is to characterise how a tennis player deals with entering vibration waves or how he/she has the ability to finely adjust them. A specific experimental procedure was designed, based on simultaneously collecting sets of kinematic, vibration and electromyographic data during forehand strokes using various commercial rackets and stroke intensities. Using 14 expert players, a wide range of excitations at spectral and temporal levels were investigated. Energetic and spectral descriptors of stroke-induced vibration occurring at the racket handle and at the player's wrist and elbow were computed. Results indicated that vibrational characteristics are strongly governed by grip force and to a lower extent by the racket properties. Grip force management drives the amount of energy, as well as its distribution, into the forearm. Furthermore, hand-grip can be assimilated to an adaptive filter which can significantly modify the spectral parameters propagating into the player's upper limb. A significant outcome is that these spectral characteristics are as much dependent on the player as on the racket. This contribution opens up new perspectives in equipment manufacture by underlining the need to account for player/racket interaction in the design process.

The effects of player grip on the dynamic behaviour of a tennis racket.

The aim of this article is to characterise the extent to which the dynamic behaviour of a tennis racket is dependent on its mechanical characteristics and the modulation of the player's grip force. This problem is addressed through steps involving both experiment and modelling. The first step was a free boundary condition modal analysis on five commercial rackets. Operational modal analyses were carried out under "slight", "medium" and "strong" grip force conditions. Modal frequencies and damping factors were then obtained using a high-resolution method. Results indicated that the dynamic behaviour of a racket is not only determined by its mechanical characteristics, but is also highly dependent on the player's grip force. Depending on the grip force intensity, the first two bending modes and the first torsional mode frequencies respectively decreased and increased while damping factors increased. The second step considered the design of a phenomenological hand-gripped racket model. This model is fruitful in that it easily predicts the potential variations in a racket's dynamic behaviour according to the player's grip force. These results provide a new perspective on the player/racket interaction optimisation by revealing how grip force can drive racket dynamic behaviour, and hence underlining the necessity of taking the player into account in the racket design process.

Neuro-mechanical adjustments to shod versus barefoot treadmill runs in the acute and delayed stretch-shortening cycle recovery phases.

In habitually shod recreational runners, we studied the combined influence of footwear and stretch-shortening cycle (SSC) fatigue on treadmill running pattern, paying special attention to neuro-mechanical adjustments in the acute and 2-day delayed recovery periods. The SSC exercise consisted of a series of 25 sub-maximal rebounds on a sledge apparatus repeated until exhaustion. The acute and delayed functional fatigue effects were quantified in a maximal drop jump test. The neuro-mechanical adjustments to fatigue were examined during two submaximal treadmill run tests of 3 min performed either barefoot or with shoes on. Surface electromyographic (EMG) activities, tibial accelerations and kinematics of the right lower limb were recorded during the first and last 15 s of each run. The main result was that neuro-mechanical differences between the shod and barefoot running patterns, classically reported in the absence of fatigue, persisted in the fatigued state. However, in the delayed recovery phase, rearfoot eversion was found to significantly increase in the shod condition. This specific footwear effect is considered as a potential risk factor of overuse injuries in longer runs. Therefore, specific care should be addressed in the delayed recovery phase of SSC fatigue and the use of motion control shoes could be of interest.

Effects of task and age on the magnitude and structure of force fluctuations: insights into underlying neuro-behavioral processes.

BACKGROUND: The present study aimed at characterizing the effects of increasing (relative) force level and aging on isometric force control. To achieve this objective and to infer changes in the underlying control mechanisms, measures of information transmission, as well as magnitude and time-frequency structure of behavioral variability were applied to force-time-series. RESULTS: Older adults were found to be weaker, more variable, and less efficient than young participants. As a function of force level, efficiency followed an inverted-U shape in both groups, suggesting a similar organization of the force control system. The time-frequency structure of force output fluctuations was only significantly affected by task conditions. Specifically, a narrower spectral distribution with more long-range correlations and an inverted-U pattern of complexity changes were observed with increasing force level. Although not significant older participants displayed on average a less complex behavior for low and intermediate force levels. The changes in force signal's regularity presented a strong dependence on time-scales, which significantly interacted with age and condition. An inverted-U profile was only observed for the time-scale relevant to the sensorimotor control process. However, in both groups the peak was not aligned with the optimum of efficiency. CONCLUSION: Our results support the view that behavioral variability, in terms of magnitude and structure, has a functional meaning and affords non-invasive markers of the adaptations of the sensorimotor control system to various constraints. The measures of efficiency and variability ought to be considered as complementary since they convey specific information on the organization of control processes. The reported weak age effect on variability and complexity measures suggests that the behavioral expression of the loss of complexity hypothesis is not as straightforward as conventionally admitted. However, group differences did not completely vanish, which suggests that age differences can be more or less apparent depending on task properties and whether difficulty is scaled in relative or absolute terms.

Shoe drop has opposite influence on running pattern when running overground or on a treadmill.

PURPOSE: Minimalist running shoes are designed to induce a foot strike made more with the forepart of the foot. The main changes made on minimalist shoe consist in decreasing the height difference between fore and rear parts of the sole (drop). Barefoot and shod running have been widely compared on overground or treadmill these last years, but the key characteristic effects of minimalist shoes have been yet little studied. The purpose of this study is to find whether the shoe drop has the same effect regardless of the task: overground or treadmill running. METHODS: Twelve healthy male subjects ran with three shoes of different drops (0, 4, 8 mm) and barefoot on a treadmill and overground. Vertical ground reaction force (vGRF) (transient peak and loading rate) and lower limb kinematics (foot, ankle and knee joint flexion angles) were observed. RESULTS: Opposite footwear effects on loading rate between the tasks were observed. Barefoot running induced higher loading rates during overground running than the highest drop condition, while it was the opposite during treadmill running. Ankle plantar flexion and knee flexion angles at touchdown were higher during treadmill than overground running for all conditions, except for barefoot which did not show any difference between the tasks. CONCLUSIONS: Shoe drop appears to be a key parameter influencing running pattern, but its effects on vGRF differ depending on the task (treadmill vs. overground running) and must be considered with caution. Unlike shod conditions, kinematics of barefoot condition was not altered by treadmill running explaining opposite conclusions between the tasks.

Estimation of hand and wrist muscle capacities in rock climbers.

PURPOSE: This study investigated the hand and wrist muscle capacities among expert rock climbers and compared them with those of non-climbers. The objective was to identify the adaptations resulting from several years of climbing practice. METHODS: Twelve climbers (nine males and three females) and 13 non-climber males participated in this study. Each subject performed a set of maximal voluntary contractions about the wrist and the metacarpo-phalengeal joints during which net joint moments and electromyographic activities were recorded. From this data set, the muscle capacities of the five main muscle groups of the hand (wrist flexors, wrist extensors, finger flexors, finger extensors and intrinsic muscles) were estimated using a biomechanical model. This process consisted in adjusting the physiological cross-sectional area (PCSA) and the maximal muscle stress value from an initial generic model. RESULTS: Results obtained from the model provided several new pieces of information compared to the analysis of only the net joint moments. Particularly, the capacities of the climbers were 37.1 % higher for finger flexors compared to non-climbers and were similar for finger extensor and for the other muscle groups. Climbers thus presented a greater imbalance between flexor and extensor capacities which suggests a potential risk of pathologies. CONCLUSIONS: The practice of climbing not only increased the strength of climbers but also resulted in specific adaptations among hand muscles. The proposed method and the obtained data could be re-used to optimize the training programs as well as the rehabilitation processes following hand pathologies.

Influence of short-term unweighing and reloading on running kinetics and muscle activity.

PURPOSE: In running, body weight reduction is reported to result in decreased lower limb muscle activity with no change in the global activation pattern (Liebenberg et al. in J Sports Sci 29:207-214). Our study examined the acute effects on running mechanics and lower limb muscle activity of short-term unweighing and reloading conditions while running on a treadmill with a lower body positive pressure (LBPP) device. METHOD: Eleven healthy males performed two randomized running series of 9 min at preferred speed. Each series included three successive running conditions of 3 min [at 100 % body weight (BW), 60 or 80 % BW, and 100 % BW]. Vertical ground reaction force and center of mass accelerations were analyzed together with surface EMG activity recorded from six major muscles of the left lower limb for the first and last 30 s of each running condition. Effort sensation and mean heart rate were also recorded. RESULT: In both running series, the unloaded running pattern was characterized by a lower step frequency (due to increased flight time with no change in contact time), lower impact and active force peaks, and also by reduced loading rate and push-off impulse. Amplitude of muscle activity overall decreased, but pre-contact and braking phase extensor muscle activity did not change, whereas it was reduced during the subsequent push-off phase. CONCLUSION: The combined neuro-mechanical changes suggest that LBPP technology provides runners with an efficient support during the stride. The after-effects recorded after reloading highlight the fact that 3 min of unweighing may be sufficient for updating the running pattern.

Handle Shape Affects the Grip Force Distribution and the Muscle Loadings During Power Grip Tasks.

The objectives of this study were to investigate the effect of handle shape on the grip force distribution in the hand and on the muscle forces during maximal power grip tasks. Eleven subjects maximally grasped 3 handles with different external shapes (circular, elliptic, and double-frustum). A handle dynamometer, equipped with both a force sensor and a pressure map, was used to record the forces exerted at the hand/handle interface. The finger and wrist joint postures were also computed from synchronized kinematic measurement. These processed data were then used as input of a biomechanical hand model to estimate muscle forces. The results showed that handle shape influences the maximal grip force, the grip force distribution, and the finger joint postures. Particularly, we observed that the elliptical shape resulted in a 6.6% lower maximal grip force compared with the circular and double-frustum handle. Concomitantly, the estimated muscle forces also varied significantly according to the handle shape, with up to 48% differences for the flexor digitorum superficialis muscle for example. Interestingly, different muscle coordination strategies were observed depending on the handle shape, therefore suggesting a potential influence of these geometrical characteristics on pathological risks such as tendonitis.

TMS reveals a direct influence of spinal projections from human SMAp on precise force production.

The corticospinal (CS) system plays an important role in fine motor control, especially in precision grip tasks. Although the primary motor cortex (M1) is the main source of the CS projections, other projections have been found, especially from the supplementary motor area proper (SMAp). To study the characteristics of these CS projections from SMAp, we compared muscle responses of an intrinsic hand muscle (FDI) evoked by stimulation of human M1 and SMAp during an isometric static low-force control task. Subjects were instructed to maintain a small cursor on a target force curve by applying a pressure with their right precision grip on a force sensor. Neuronavigated transcranial magnetic stimulation was used to stimulate either left M1 or left SMAp with equal induced electric field values at the defined cortical targets. The results show that the SMAp stimulation evokes reproducible muscle responses with similar latencies and amplitudes as M1 stimulation, and with a clear and significant shorter silent period. These results suggest that (i) CS projections from human SMAp are as rapid and efficient as those from M1, (ii) CS projections from SMAp are directly involved in control of the excitability of spinal motoneurons and (iii) SMAp has a different intracortical inhibitory circuitry. We conclude that human SMAp and M1 both have direct influence on force production during fine manual motor tasks.

Aging of running shoes and its effect on mechanical and biomechanical variables: implications for runners.

This study investigates the effect of running shoes' aging on mechanical and biomechanical parameters as a function of midsole materials (viscous, intermediate, elastic) and ground inclination. To this aim, heel area of the shoe (under calcaneal tuberosity) was first mechanically aged at realistic frequency and impact magnitudes based on a 660 km training plan. Stiffness (ST) and viscosity were then measured on both aged and matching new shoes, and repercussions on biomechanical variables (joint kinematics, muscular pre-activation, vertical ground reaction force and tibial acceleration) were assessed during a leg-extended stepping-down task designed to mimic the characteristics of running impacts. Shoes' aging led to increased ST (means: from 127 to 154 N ∙ mm(-1)) and decreased energy dissipation (viscosity) (means: from 2.19 to 1.88 J). The effects induced by mechanical changes on body kinematics were very small. However, they led with the elastic shoe to increased vastus lateralis pre-activation, tibial acceleration peak (means: from 4.5 g to 5.2 g) and rate. Among the three shoes tested, the shoe with intermediate midsole foam provided the best compromise between viscosity and elasticity. The optimum balance remains to be found for the design of shoes regarding at once cushioning, durability and injury prevention.

A multi-level approach to investigate the control of an input device: application to a realistic pointing task.

This study investigates the subjects' performance during realistic conditions of control of a joystick. An adapted reciprocal aiming task consisting in driving a virtual vehicle along a slalom course as fast as possible was performed while accuracy constraints were manipulated. Realistic dynamical Interface Screen Relationship between the joystick displacements and the displacements of the vehicle was simulated. Vehicle displacements and motor activity (muscle activity and joint kinematics) were recorded. The results highlighted the applicability of the Fitts' law to more realistic conditions where the use of an input device is performed in an intensive control situation. Besides, biomechanical results suggested that neuromuscular responses were different regarding the direction of movement, whereas the performance at a behavioural level were not affected. Thus, this study demonstrates the interest in considering two different aspects of the user's performance (behavioural and biomechanical ones) to make a better agreement between the device design and users' needs. PRACTITIONER SUMMARY: This study considered two different aspects of the subject's performance in a realistic situation of speed­accuracy trade-off: the behavioural and motor activity. The necessity for the design of the future ergonomics pointing devices to meet the expectations of the neuromuscular system in order to facilitate their uses is highlighted.

Age-related changes of movement patterns in discrete Fitts' task.

BACKGROUND: Inspired by the framework of dynamical system theory, we aimed at exploring how the behavioural repertoire of the sensorimotor system can be reshaped with aging. Our reasoning was founded on the assumption that, with age, some of the existing patterns can be destabilized or even lost. In the present paper, this issue was investigated through the study of age-related changes in the movement patterns that are used to perform a discrete Fitts' task. We analysed the performance of two groups of participants (young and older adults) across nine task difficulty levels, obtained via manipulation of target width. RESULTS: Two movement patterns were revealed by the fact that increase in the index of the difficulty (ID) was accommodated through either the lengthening of both acceleration (AT) and deceleration (DT) times (co-variation pattern), or only DT (dissociation pattern). Analysis of the discontinuity in ID-AT relation showed that young participants switched from the co-variation to the dissociation pattern as ID increased. Pattern switching was accompanied by concomitant changes in the variability of AT/DT ratio. Older adults, on the other hand, used the dissociation pattern regardless of the ID. Consequently, they showed neither an abrupt discontinuity in ID-AT relation nor significant changes in the variability of AT/DT ratio across difficulty levels. Though the dissociation pattern was adaptive in young adults for high accuracy constraints, in older adults, it compromised task performance for lower difficulty levels. CONCLUSION: These findings support the view that aging may result in a compression of the neuro-behavioural repertoire. In sensorimotor tasks, it can lead to a loss of multi-stability in terms of available movement patterns, thereby compromising the ability of the neuro-musculo-skeletal system to adapt and face task constraints.

Aging of sensorimotor processes: a systematic study in Fitts' task.

Though age-related decrease in information-processing capacities is hypothesized to be a prominent cause of behavioral slowing, it has been scarcely systematically studied in goal-directed motor tasks. The present study investigated how the decrease in information processing affects the sensorimotor processes underlying the control of a discrete Fitts' task. The index of difficulty (ID) of the task was manipulated using changes in either target distance (D) or target width (W). In each manipulation, movement (MTs), acceleration (ATs) and deceleration times (DTs) of young and older participants were compared across eight ID levels. They were analyzed with efficiency functions, state traces and Brinley plots. Our results showed that older participants were always slower. However, in both age groups, MTs were longer in D manipulation, which resulted from a slowing of both ATs and DTs, while W manipulation affected mainly DTs. In D manipulation, equivalent age-related slowing ratios were observed for AT and DT (1.3). In W manipulation, ATs of older participants were additively slower than those of young participants. Conversely, DTs presented a multiplicative slowing ratio of 1.3. These findings showed that ID manipulations differentially loaded information processing in the nervous system and that age-related slowing of multisensory control processes was independent of the manipulated dimension. Nevertheless, ID manipulations revealed different age-related adaptations to task constraints, suggesting that D and W manipulations are complementary means to assess age-related slowing of the processes involved in target-directed rapid-aiming tasks, with D scaling being more specific to capture the slowing of force-impulse control.