Assessing mechanical ankle instability via functional 3D stress-MRI - A pilot study.

BACKGROUND: Quantitative measurement of the mechanical deficit in chronic ankle instability (CAI) is difficult. Therefore, the distinction between functional (FAI) and mechanical ankle instability (MAI) as well as the evaluation of surgical techniques is difficult. This pilot study uses a novel method of functional 3-dimensional stress ankle-MRI to test its applicability for assessing mechanical ankle instability. METHODS: We used a custom-built ankle arthrometer that allows a stepless positioning of the foot and an axial in situ loading with up to 500 N combined with a 3-dimensional MRI protocol. We assessed four parameters (3D cartilage contact area (CCA) fibulotalar, tibiotalar horizontal and vertical and intermalleolar distance) under six different conditions (neutral-null, plantarflexion-supination and dorsiflexion-pronation each with and without loading) in n = 10 individuals (7 suffering from MAI and 3 healthy controls). FINDINGS: The MAI group showed a substantially increased reduction of lateral osseous constraint compared to healthy controls when the foot was positioned in plantarflexion-supination (CCA fibulotalar 69% vs. 30% in controls). The reduction of the weight bearing surface in plantarflexion-supination was also more pronounced (CCA tibiotalar horizontal -49% in MAI vs. -28% in controls). INTERPRETATION: This novel technique is valuable for assessing mechanical ankle instability in the target population and has a potential clinical benefit for assessing the mechanical deficit of individual patients. Further studies are needed to provide evidence for a possible prognostic value of this novel technique.

It's never too late - balance and endurance training improves functional performance, quality of life, and alleviates neuropathic symptoms in cancer survivors suffering from chemotherapy-induced peripheral neuropathy: results of a randomized controlled trial.

BACKGROUND: Chemotherapy-induced peripheral neuropathy (CIPN) can affect functional performance and quality of life considerably. Since balance training has proven to enhance physical function, it might be a promising strategy to manage CIPN-induced functional impairments. METHODS: Fifty cancer survivors with persisting CIPN after finishing their treatment were randomly allocated to an intervention (IG) or active control group (CG). The IG did endurance plus balance training, the CG only endurance training (twice weekly over 12 weeks). Pre- and post-assessments included functional performance, cardiorespiratory fitness, vibration sense, and self-reported CIPN symptoms (EORTC QLQ-CIPN20). RESULTS: Intention-to-treat analyses (n = 41) did not reveal a significant group difference (CG minus IG) for sway path in semi-tandem stance after intervention (primary endpoint), adjusted for baseline. However, our per-protocol analysis of 37 patients with training compliance ≥70% revealed: the IG reduced their sway path during semi-tandem stance (- 76 mm, 95% CI -141 - -17; CG: -6 mm, 95% CI -52 - 50), improved the duration standing on one leg on instable surface (11 s, 95% CI 8-17; CG: 0 s, 95%CI 0-5) and reported decreased motor symptoms (-8points, 95% CI -18 - 0; CG: -2points 95% CI -6 - 2). Both groups reported reduced overall- (IG: -10points, 95% CI -17 - -4; CG: -6points, 95% CI -11 - -1) and sensory symptoms (IG: -7points, 95% CI -15 - 0; CG: -7points, 95% CI -15 - 0), while only the CG exhibited objectively better vibration sense (knuckle: 0.8points, 95% CI 0.3-1.3; IG: 0.0points, 95% CI -1.1 - 0.9; patella: 1.0points, 95% CI 0.4-1.6: IG: -0.8points, 95% CI -0.2 - 0.0). Furthermore, maximum power output during cardiopulmonary exercise test increased in both groups (IG and CG: 0.1 W/kg, 95% CI 0.0-0.2), but only the CG improved their jump height (2 cm, 95% CI 0.5-3.5; IG: 1 cm, 95% CI -0.4 - 3.2). CONCLUSION: We suppose that endurance training induced a reduction in sensory symptoms in both groups, while balance training additionally improved patients' functional status. This additional functional effect might reflect the IG's superiority in the CIPN20 motor score. Both exercises provide a clear and relevant benefit for patients with CIPN. TRIAL REGISTRATION: German Clinical Trials Register (DRKS) number: DRKS00005419 , prospectively registered on November 19, 2013.

Effects of perturbation or plyometric training on core control and knee joint loading in women during lateral movements.

Deficits in trunk control are argued to increase the risk of knee injuries. However, no existing training program effectively addresses trunk control during lateral movements, such as cutting maneuvers. The purpose of this study was to investigate whether a combination of perturbation and plyometric training (PPT) would reduce trunk excursions against the new movement direction and reduce knee joint moments during lateral movements. Twenty-four active women participated in a RCT, where trunk and pelvis kinematics and knee joint moments were measured during lateral reactive jumps (LRJ) and unanticipated cutting maneuvers before and after a 4-week PPT program and compared to a control group. During LRJ, trunk rotation away from the new movement direction was reduced (P < 0.001), while pelvis rotation toward the new direction was increased (P = 0.006) after PPT. Moreover, decreased knee extension moments (P = 0.028) and knee internal rotation moments (P < 0.001) were reported after both trainings. Additionally, PPT reduced trunk rotation by 7.2° during unanticipated cuttings. A 4-week PPT improved core control by reducing trunk rotation and reduced knee joint moments during LRJ. During training, perturbations should be introduced to improve core control during dynamic athletic movements, possibly reducing the risk of ACL injuries.

Acute corticospinal and spinal modulation after whole body vibration.

OBJECTIVES: The objective of this study was to investigate neural effects of acute whole body vibration (WBV) on lower limb muscles regarding corticospinal and spinal excitability. METHODS: In 44 healthy subjects (16 f/ 28 m), motor evoked potentials (MEP) and H-reflexes in m. soleus (SOL) and gastrocnemius medialis (GM) were elicited before (t1), immediately after (t2), 2 (t3), 4 (t4) and 10 min after (t5) WBV. RESULTS: After WBV, MEP amplitudes were significantly increased in SOL (t2+15±30%, t3+22±32%, t4+15±35%, t5+20±30%, P<0.05), but not in GM (t2+32±62%, t3+9±35%, t4+8±36%, t5+22±47%; P=0.07). Contrarily, H-reflexes were significantly reduced in SOL (t2-19±28%, t3-21±22%, t4-20±21%, t5-14±28%, P<0.05) and GM (t2-14±37%, t3-16±25%, t4-18±29%, t5-16±28%, P<0.05). CONCLUSIONS: A temporary sustained enhancement of corticospinal excitability concomitant with spinal inhibition after WBV points towards persisting neural modulation in the central nervous system. This could indicate greater neural modulation over M1 and descending pathways, while the contribution of spinal pathways is reduced.

Using Thorax Expansion to Detect a Ventilatory Inflection Point in the Field.

Assessing an individual's physical fitness can usually be achieved through evaluating lactate or ventilatory thresholds. Unfortunately, the detection of ventilatory thresholds still requires uncomfortable mass flow sensors and a laboratory setting. Therefore, this study aimed to evaluate a ventilatory inflection point (VIP) derived from thorax expansion as a useful surrogate to assess an individual's physical fitness under field conditions. 348 and 107 ramp tests have been selected respectively to examine validity and retest variability of VIP. The individual anaerobic threshold (IAT) determined by means of blood lactate sampling was used as reliable rationale for evaluation. Calibrated respiratory inductance plethysmography (RIP) was utilized to derive ventilation from thorax expansion during the ramp test. An automated software routine was applied to detect the VIP. Speed, heart rate and ventilation at the VIP correlated significantly to corresponding values at IAT (r=0.840, 0.876, 0.933). Non-systematic differences between repeated testing ranged within ±1.15 km·h(-1), ±8.74 b·min(-1) and ±12.69 l·min(-1) (±1.96 SD). The timing of VIP is not solely dependent on the aerobic capacity and might instead quantify an individual's physical fitness in terms of the efficiency of the compensative and supportive ventilatory response during increased exercise intensities.

Influence of Gender on Trunk and Lower Limb Biomechanics during Lateral Movements.

This study investigates gender differences in lateral trunk lean to confound possible associations with hip and knee joint biomechanics during lateral reactive jumps. Twelve female and 12 male athletes performed lateral reactive jumps while three-dimensional knee, hip and trunk kinematics as well as ground reaction forces and electromyography of selected thigh muscles were recorded. Lateral trunk lean did not differ between genders, while females had greater knee valgus angle than males (-4.9 ± 3.9° vs. 1.6 ± 3.2°, p = 0.001). A significant association between the lateral trunk lean and the hip abduction moment (r = 0.55) was found. Moreover, lateral trunk lean and knee abduction moment showed a significant relationship (r = 0.67). The positive association between trunk lean and knee abduction moment suggests that higher lateral trunk lean may increase the risk of knee injury during lateral movements and that the trunk should be trained accordingly in team sports.

A wearable respiratory monitoring device--the between-days variability of calibration.

The between-days variability in ascertained gain factors for calibration of a wearable respiratory inductance plethysmograph (RIP) and validity thereof for the repeated use during exercise were examined. Consecutive 5-min periods of standing still, slow running at 8 km·h(-1), fast running at 14 km·h(-1) (male) or 12 km·h(-1) (female) and recovery were repeated by 10 healthy subjects on 5 days. Breath-by-breath data were recorded simultaneously by flow meter and RIP. Gain factors were determined individually for each trial (CALIND) via least square regression. Reliability and variability in gain factors were quantified respectively by intraclass correlation coefficients (ICC) and limits of agreement. Within a predefined error range of ±20% the amount of RIP-derived tidal volumes after CALIND was compared to corresponding amounts when gain factors of the first trial were applied on the following 4 trials (CALFIRST). ICC ranged within 0.96 and 0.98. The variability in gain factors (up to ± 24.06%) was reduced compensatively by their sum. Amounts of breaths within the predefined error range did not differ between CALIND and (CALFIRST) (P>0.32). The between-days variability of gain factors for a wearable RIP-device does not show impaired reliability in further derived tidal volumes.

Improved postural control in response to a 4-week balance training with partially unloaded bodyweight.

Balance training (BT) is successfully implemented in therapy as a countermeasure against postural dysfunctions. However, patients suffering from motor impairments may not be able to perform balance rehabilitation with full body load. The purpose of this study was to investigate whether partial unloading leads to the same functional and neuromuscular adaptations. The impact on postural control of a 4-week BT intervention has been compared between full and partial body load. 32 subjects were randomly assigned to a CON (conventional BT) or a PART group (partially unloaded BT). BT comprised balance exercises addressing dynamic stabilization in mono- and bipedal stance. Before and after training, centre of pressure (COP) displacement and electromyographic activity of selected muscles were monitored during different balance tasks. Co-contraction index (CCI) of soleus (SOL)/tibialis (TA) was calculated. SOL H-reflexes were elicited to evaluate changes in the excitability of the spinal reflex circuitry. Adaptations in response to the training were in a similar extent for both groups: (i) after the intervention, the COP displacement was reduced (P<0.05). This reduction was accompanied by (ii) a decreased CCI of SOL/TA (P<0.05) and (iii) a decrease in H-reflex amplitude (P<0.05). BT under partial unloading led to reduced COP displacements comparable to conventional BT indicating improved balance control. Moreover, decreased co-contraction of antagonistic muscles and reduced spinal excitability of the SOL motoneuron pool point towards changed postural control strategies generally observed after full body load training. Thus, BT considering partial unloading is an appropriate alternative for patients unable to conduct BT under full body load.

Exercise program improves therapy-related side-effects and quality of life in lymphoma patients undergoing therapy.

BACKGROUND: Lymphoma patients undergoing therapy must cope with the side-effects of the disease itself, therapy and associated immobility. Peripheral neuropathy (PNP), loss of balance control and weakness not only diminishes patients' quality of life (QOL), it can also affect planning and the dosage of therapy. Exercise may enable patients to reverse these declines, improving their performance level and QOL. PATIENTS AND METHODS: We carried out a randomized, controlled trial, assigning 61 lymphoma patients either to a control group (CG; N=31) or to a 36-week intervention (IG; N=30), consisting of sensorimotor-, endurance- and strength training twice a week. Primary end point was QOL; secondary end points included movement coordination, endurance, strength and therapy-induced side-effects. RESULTS: Intergroup comparison revealed improved QOL- (ΔT1-T0; P=0.03) and PNP-related deep sensitivity in the IG: 87.5% were able to reduce the symptom, compared with 0% in the CG (P<0.001). Significant differences in the change of balance control could be found between the groups, with the IG improving while the CG steadily declined (monopedal static ΔT3-T0; P=0.03; dynamic ΔT3-T0; P=0.007; perturbed mono-ΔT3-T0; P=0.009 and bipedal ΔT3-T0; P=0.006), failed attempts (monopedal static ΔT3-T0; P=0.02, dynamic ΔT3-T0; P<0.001and perturbed ΔT3-T0; P=0.006) and improved time to regain balance (ΔT3-T0; P=0.04). Moreover, the change in the aerobic performance level (ΔT3-T0; P=0.05) and additional amount of exercise carried out per week [metabolic equivalent (MET); P=0.02] differed significantly across groups. CONCLUSIONS: Exercise, especially sensorimotor training, is a feasible and promising method to support cancer patients during therapy. It improves patients QOL, reduces restrictions from side-effects such as PNP and improves patients' balance control, physical performance level and mobility. GERMAN CLINICAL TRIALS REGISTER NUMBER: DRKS00003894.

Knee and hip joint biomechanics are gender-specific in runners with high running mileage.

Female runners are reported to be more prone to develop specific knee joint injuries than males. It has been suggested that increased frontal plane joint loading might be related to the incidence of these knee injuries in running. The purpose of this study was to evaluate if frontal plane knee and hip joint kinematics and kinetics are gender-specific in runners with high mileage. 3D-kinematics and kinetics were recorded from 16 female and 16 male runners at a speed of 3 m/s, 4 m/s, and 5 m/s. Frontal plane joint angles and joint moments were ascertained and compared between genders among speed conditions. Across all speed conditions, females showed increased hip adduction and reduced knee adduction angles compared to males (p < 0.003). The initial peak in the hip adduction moment was enhanced in females (p = 0.003). Additionally, the hip adduction impulse showed a trend towards an increase in females at slow running speed (p = 0.07). Hip and knee frontal plane joint kinematics are gender-specific. In addition, there are indications that frontal plane joint loading is increased in female runners. Future research should focus on the relationship of these observations regarding overuse running injuries.

The effect of whole body vibration on the H-reflex, the stretch reflex, and the short-latency response during hopping.

The effect of whole body vibration (WBV) on reflex responses is controversially discussed in the literature. In this study, three different modalities of reflex activation with increased motor complexity have been selected to clarify the effects of acute WBV on reflex activation: (1) the electrically evoked H-reflex, (2) the mechanically elicited stretch reflex, and (3) the short-latency response (SLR) during hopping. WBV-induced changes of the H-reflex, the stretch reflex, and the SLR during hopping were recorded in the soleus and gastrocnemius muscles and were analyzed before, during (only the H-reflex), immediately after, 5 min and 10 min after WBV. The main findings were that (1) the H-reflexes were significantly reduced during and at least up to 5 min after WBV, (2) the stretch reflex amplitudes were also significantly reduced immediately after WBV but recovered to their initial amplitudes within 5 min, and (3) the SLR during hopping showed no vibration-induced modulation. With regard to the modalities with low motor complexities, the decreased H- and stretch reflex responses are assumed to point toward a reduced Ia afferent transmission during and after WBV. However, it is assumed that during hopping, the suppression of reflex sensitivity is compensated by facilitatory mechanisms in this complex motor task.

"Obese equals lazy?" analysis of the association between weight status and physical activity in children.

INTRODUCTION: Literature provides evidence that overweight children are more sedentary. To verify this generalized statement behavior patterns of overweight and nonoverweight children needs to be understood. Therefore, we investigated the distribution of sedentary and activity levels in a quantitative and qualitative way. METHODS: Data was collected from 37 randomly selected nonoverweight and 55 overweight children. They were 8 to 11 years of age. Height and weight were measured and weight status was characterized by BMI (BMI-percentile, BMI-SDS). Daily PA (physical activity) was measured by direct accelerometry. Spare time and screen time entertainment were obtained by questionnaires. RESULTS: The amount of time spent "passive" was significantly higher in overweight children, while nonoverweight children were more "active." The multiple regression model shows a significant association between weight status (BMI-SDS) and activity parameters. Additionally, screen time entertainment was significantly related to BMI-SDS. CONCLUSION: The results support the statement that overweight children are less active than nonoverweight children. The high amount of PA seems to be an important factor to prevent overweight in children given that PA shows the highest correlation to weight status. Quantitative and qualitative measurements are needed for further analysis.

[Ankle arthrometry for evaluation of the mechanical component in chronic ankle instability]. / Sprunggelenkarthrometrie zur Diagnostik der mechanischen Komponente der chronischen Sprunggelenkinstabilität.

BACKGROUND: Chronic ankle instability (CAI) is a term that is not well defined until now in spite of a large body of respective literature. Most frequently this umbrella term is used synonymously for functional ankle instability and the role of the mechanical component is not fully understood. PATIENTS/MATERIAL AND METHODS: In a cohort consisting of 15 patients suffering from CAI we preoperatively investigated the mechanical component using both stress radiographs and ankle arthrometry. The functional impact was measured with the FAAM-G (foot and ankle ability measure, German version). The results were compared with a respective group of 17 uninjured subjects. RESULTS: Relevant differences were found between the patients and the uninjured groups in the mechanical (stiffness in the 40 - 60 N region of the load deformation curves and the ratio between stiffness in the 125 - 175 N and 40 - 60 N region) and functional analyses (FAAM-G), respectively (p < 0.001 - 0.040). There was no difference found between groups in the upper (125 - 175 N) region of the load deformation curves. CONCLUSIONS: This article helps to clarify the role of the mechanical component in CAI. Patients suffering from both functional and mechanical ankle instability can be detected with the FAAM-G questionnaire and with different ankle stiffness parameters from ankle arthrometer stress testing. These measures differentiate CAI patients from uninjured persons with functionally and mechanically stable ankles. Therefore, these instruments can be recommended to diagnose and quantify the mechanical component in CAI.

How to sprain your ankle - a biomechanical case report of an inversion trauma.

In order to develop preventive measures against lateral ankle sprains, it is essential to have a detailed understanding of the injury mechanism. Under laboratory experimental conditions the examination of the joint load has to be restricted with clear margins of safety. However, in the present case one athlete sprained his ankle while performing a run-and-cut movement during a biomechanical research experiment. 3D kinematics, kinetics, and muscle activity of the lower limb were recorded and compared to 16 previously performed trials. Motion patterns of global pelvis orientation, hip flexion, and knee flexion in the sprain trail deviated from the reference trials already early in the preparatory phase before ground contact. During ground contact, the ankle was rapidly plantar flexed (up to 1240°/s), inverted (up to 1290°/s) and internally rotated (up to 580°/s) reaching its maximum displacement within the first 150 ms after heel strike. Rapid neuromuscular activation bursts of the m. tibialis anterior and the m. peroneus longus started 40-45 ms after ground contact and overshot the activation profile of the reference trials with peak activation at 62 ms and 74 ms respectively. Therefore, it may be suggested that neuromuscular reflexes played an important role in joint control during the critical phase of excessive ankle displacement. The results of this case report clearly indicate that (a) upper leg mechanics, (b) pre-landing adjustments, and (c) neuromuscular contribution have to be considered in the mechanism of lateral ankle sprains.

Leg stiffness can be maintained during reactive hopping despite modified acceleration conditions.

AIM: The aim of the present study was to evaluate reactive hops under systematically modified acceleration conditions. It was hypothesized that a high preactivity of the leg extensors and phase-specific adjustments of the leg muscle activation would compensate the alterations caused by the various acceleration levels in order to maintain a high leg stiffness, thus enabling the jumper to perform truly reactive jumps with short ground contact times despite the unaccustomed acceleration conditions. METHODS: Ground reaction forces (GRF), kinematic and electromyographic data of 20 healthy subjects were recorded during reactive hopping in a special sledge jump system for seven different acceleration levels: three acceleration levels with lower than normal gravity (0.7g, 0.8g, 0.9g), one with gravitational acceleration (1g) and three with higher acceleration (1.1g, 1.2g, 1.3g). RESULTS: The increase of the acceleration from 0.7g to 1.3g had no significant effect on the preactivity of the leg extensors, the leg stiffness and the rate of force development. However, it resulted in increased peak GRF (+15%), longer ground contact time (+10%) and increased angular excursion at the ankle and knee joints (+3°). DISCUSSION: Throughout a wide acceleration range, the subjects were able to maintain a high leg stiffness and perform reactive hops by keeping the preactivity constantly high and adjusting the muscle activity in the later phases. In consequence, it can be concluded that the neuromuscular system can cope with different acceleration levels, at least in the acceleration range used in this study.

The drop height determines neuromuscular adaptations and changes in jump performance in stretch-shortening cycle training.

There is an ongoing discussion about how to improve jump performance most efficiently with plyometric training. It has been proposed that drop height influences the outcome, although longitudinal studies are missing. Based on cross-sectional drop jump studies showing height-dependent Hoffmann (H)-reflex activities, we hypothesized that the drop height should influence the neuromuscular activity and thus, the training result. Thirty-three subjects participated as a control or in one of two stretch-shortening cycle (SSC) interventions. Subjects either trained for 4 weeks doing drop jumps from 30, 50, and 75 cm drop heights (SSC1) or completed the same amount of jumps exclusively from 30 cm (SSC2). During training and testing (from 30, 50, and 75 cm), subjects were instructed to minimize the duration of ground contact and to maximize their rebound height. Rebound heights were significantly augmented after SSC1, but a trend was only observed after SSC2. In contrast, the duration of ground contact increased after SSC1 but decreased after SSC2. The performance index (rebound height/duration of ground contact) improved similarly after SSC1 (+14%) and SSC2 (+14%). Changes in performance were accompanied by neuromuscular adaptations: for SSC1, activity of the soleus increased toward take-off (between 120 and 170 ms after touchdown), whereas SSC2-trained subjects showed enhanced activity shortly after ground contact (20-70 ms after touch down). The present study demonstrates a strong link among drop height, neuromuscular adaptation, and performance in SSC training. As the improvement in the performance index was no different after SSC1 or SSC2, the decision whether to apply SSC1 or SSC2 should depend on the specific requirements of the sports discipline.

[Acute and overuse injuries in elite paracycling - an epidemiological study]. / Verletzungen und Überlastungsbeschwerden im paralympischen Radsport - eine Fragebogenerhebung bei Nationalkaderathleten.

Although paracycling is a growing discipline in high level competitive sports as well as in posttraumatic rehabilitation, epidemiological data of resulting injuries is still missing. Therefore, 19 athletes of the German national paracycling team were asked about their injuries during the 2008 season using a standardized questionnaire. Overall, 18 (94.7 %) of 19 athletes reported overuse injuries; most commonly localized at the back (83.3 %), neck/shoulder (77.8 %), knee (50 %), groin/buttock (50 %) and hands/wrists (38.9 %). Altogether, 18 accidents were registered, corresponding to an injury rate of 0,95 acute injuries per athlete per year (0,07 / 1000 km). The most common acute injuries were abrasions (69.2 %) and contusions (61.5 %), whereas fractures were stated only twice (11.8 %). The anatomical distribution of overuse injuries in disabled cyclists confirms the results of studies in able-bodied cycling, although the incidences in low-back pain and neck/shoulder pain is clearly higher in disabled cycling, as well as the rate of traumatic injuries.

Spinal reflex plasticity in response to alpine skiing in the elderly.

The present study was designed to assess the influence of 12 weeks (28.5 ± 2.6 skiing days) of alpine skiing on spinal reflex plasticity, strength and postural control in senior citizens. Therefore, soleus H-reflexes and postural stability were measured during bipedal quiet and unstable stance in 22 (12 male and 10 female) elderly subjects aged 66.6 ± 1 years. Furthermore, the maximal isometric force was determined in a leg press. The results showed an increased H-reflex excitability after the training (+39%; P<0.05) while no changes occurred in the background EMG. The postural sway decreased after training (-6.6 cm; P ≤ 0.05) and the maximal force increased (+16.1%; P<0.05). No adaptations in any parameter could be observed in the control group. The present study demonstrated that skiing training was effective to alter the spinal reflex activity in elderly individuals. The increased H-reflexes correspond to adaptations known from strength training in young subjects. It may be assumed that alpine skiing induced a functional adaptation in that subjects have learned to integrate Ia afferent feedback more efficiently to ensure adequate motoneuron output.

Effects and mechanisms of strength training in children.

It has been demonstrated that strength training can be organized in children in a safe and effective way. However, there is limited data regarding its impact on muscle hypertrophy. This study investigated the effects of a high-intensity strength training (HIS) on knee extensor/flexor strength, countermovement (CMJ) jumping height, postural control, soft lean mass and muscle cross-sectional area (CSA) of the dominant leg in prepubertal children. Thirty-two children participated in this study and were assigned to an intervention (INT; N=17) or a control class ( N=15). The INT participated in 10 weeks of weight-machine based HIS integrated in physical education. Pre/post tests included the measurements of peak torque of the knee extensors/flexors at 60 and 180°/s, CMJ jumping height, postural sway, soft lean mass of the leg by bioelectrical impedance analysis, and CSA (m. quadriceps) by magnetic resonance imaging. HIS resulted in significant increases in knee extensor/flexor peak torque (60°/s and 180°/s). HIS did not produce significant changes in CMJ jumping height, postural sway, soft lean mass, and CSA. Although HIS was effective at increasing peak torque of the knee extensors/flexors in children, it was unable to affect muscle size. It appears that neural factors rather than muscle hypertrophy account for the observed strength gains in children.