Although injury and neuromuscular activation patterns may be common for all individuals, there are certain factors which differentiate neuromuscular activity responses between children, adults and elderly. The purpose of this study is to review recent evidence on age differences in neural activation and muscle balances around the knee when performing single joint movements. Particularly, current evidence indicates that there are some interesting similarities in the neuromuscular mechanisms by which children or the elderly differ compared with adults. Both children and elderly display a lower absolute muscle strength capacity than adults which cannot fully be explained by differences in muscle mass. Quadriceps activation failure is a common symptom of all knee injuries, irrespective of age but it is likely that its effect is more evident in children or adults. While one might expect that antagonist co-activation would differ between age categories, it appears that this is not the case. Although hamstring: quadriceps ratio levels are altered after knee injury, it is not clear whether this is an age specific response. Finally, evidence suggests that both children and the elderly display less stiffness of the quadriceps muscle-tendon unit than adults which affects their knee joint function.
The purpose of this study was to compare the acute effects of three different stretching protocols on balance, agility, reaction time and movement time of the upper limbs. Participants were thirty one female high school athletes (age = 17.3 ± 0.5 yr.). All participants performed one of the following protocols on different days: (a) 3 min jogging followed by 7 min static stretching (SS), (b) 3 min jogging followed by 7 min dynamic stretching (DS), and (c) 3 min jogging followed by 7 min of rest (NS). After the protocols participants performed the following tests: dynamic balance, 505 agility test, reaction time (time between a sound stimulus and release of a button) and movement time (movement of the upper extremity over a 0.5 m distance). The order of stretching protocols and performance tests were counterbalanced to avoid carryover effects. Repeated measures analysis of variance revealed significant main effects for all variables except reaction time. The DS protocol compared to SS performed significantly better in balance, agility and movement time. Additionally, the DS protocol compared to NS performed significantly better in agility. According to the results of the study, a DS protocol is more appropriate than SS for activities that require balance, rapid change of running direction (agility) and movement time of the upper extremities. Key pointsStatic stretching has a negative effect on balance and agility performance compared to dynamic stretching.There was no effect of the stretching protocols on reaction time.Dynamic stretching was more effective than static stretching for increasing movement time of the upper extremities.
The purpose of this study was to describe the performance and biomechanical parameters of the counter-movement jump for young people with ID, in comparison with age matched individuals without ID. Volunteers with ID (n=13; age=15.3 ± 1.6 years; Wisk III intelligence quotient 55.6 ± 11.2) and without ID (n=13; age=15.4 ± 1.2 years) performed maximal counter-movement jumps, while knee kinematics, vertical ground reaction forces and electromyographic activity of the vastus lateralis and biceps femoris were captured. Individuals without ID jumped higher than their counterparts with ID and had lower take-off velocity, lower knee joint power and stiffness, lower knee joint extension angle and angular velocity, longer braking and propulsion phase, lower agonist and higher antagonist EMG activity. These results give an insight on possible causes for the performance deficit in CMJ in persons with ID and give the potential for such individuals to improve their ability to jump higher and more efficiently.
The purpose of this study was to examine central and peripheral factors of fatigability that could explain the differences in fatigability between adults and prepubertal boys after maximal sustained isometric contraction.
This study examined the post-activation potentiation (PAP) effects on squat jump (SJ) performance and on peak rate of force development (RFDpeak) in pre-adolescent (10-12 yrs.), adolescents (14-15 yrs.) and adults (20-25 yrs.) males and females. All participants performed a SJ with and without prior conditioning stimulus (PAP and control protocol, respectively), consisting of 3×3-s maximal isometric squats. Jump height and RFDpeak of the vertical ground reaction force during SJ were assessed before, and at 20 s and at 4 min following the conditioning stimulus. The results revealed a different pattern of age-effect on SJ performance within males and females. The RFDpeak significantly increased as a factor of age in both males and females (p<0.05). Increase in SJ performance after conditioning stimulus occurred only in men (p<0.05), with no effects in teen-males, boys, and female groups. There was a significant PAP effect on RFDpeak in both adult groups (p<0.05) and teen-males, with no effects in children. In conclusion, the PAP effects on SJ performance and RFDpeak are age and sex dependent; that is PAP appears as a viable method for acutely enhancing SJ performance in men but not in pediatric population.
The purpose of this study was to examine the effects of submaximal sustained contractions on fatigue and recovery properties in untrained prepubescent boys (n = 14) and men (n = 14). All participants performed, in random order, an isometric plantar flexion at 20% and 60% of their maximal voluntary contraction (MVC) until exhaustion (20%fatigue and 60%fatigue, respectively). During both fatigue protocols, surface electromyogram (sEMG) of the soleus and tibialis anterior muscles was recorded. Before and after the fatigue protocol, MVCs and blood lactate concentration were obtained. During 20%fatigue and 60%fatigue, agonist and antagonist sEMG increased gradually to a similar extent in both groups. Immediately after fatigue, MVC torque decreased in both groups, compared with prefatigue values, and boys recovered faster than men in both fatigue protocols. The reduction in agonist sEMG during MVC after fatigue was not significantly different between men and boys (p < 0.05), independent of the fatigue protocol. sEMG of boys recovered to baseline values 3 min after the 20%fatigue and 60%fatigue protocols, whereas men did not recover. Lactate concentration increased immediately after the end of the fatigue protocols, compared with the prefatigue values (p < 0.05). This increase was higher for the 60%fatigue than for 20%fatigue protocol, and did not differ between boys and men. It is concluded that low- and middle-intensity submaximal sustained isometric fatigue protocols induce similar fatigue effects in boys and men. Furthermore, it was shown that boys can recover faster than men, independent of the contraction intensity that induces fatigue.
The purpose of this study was to identify the differences in vertical squat jump (SJ) between volunteers with and without intellectual disability (ID). Thirteen boys with ID (average intelligence quotient, estimated by Wisk III test: 55.6 ± 11.2) and 13 peers without disabilities performed maximal SJ on a force platform. Kinematic data were captured using a six-camera 3D motion analysis system and electromyographic (EMG) activity was recorded using surface electrodes. Unpaired T-test determined the statistical difference between the two groups. The obtained results indicated that the group with ID, jumped lower, developed lower vertical ground reaction forces, knee power output, knee angular velocity, and take-off velocity, and showed longer propulsion duration, decreased mean to maximum agonist EMG activity and higher antagonist/agonist activity ratio. The deficit in the SJ observed in individuals with ID was attributed to a deficit in the examined mechanical and neuromuscular parameters, and especially to the agonist and antagonist co-contraction.
The aim of this study was to examine the effect of a 10-week combined resistance/sprint training programme in the post-activation potentiation of sprint performance before, between and after resistance training sets. Twenty-six junior basketball players were randomly divided into a control and a combined training group. The combined training group performed a combined training programme consisting of 5 sets at 5-8 RM (Repetition Maximum) half-squats with sprints performed between each set. Post-activation potentiation was considered as the increase in sprint velocity in trials executed between and after the resistance sets compared with the sprint trial performed before the resistance sets of the respective first and last training session. For sprint evaluation the running distances 0-10 and 0-30 m were selected. The intervention increased both strength and sprint performance. No post-activation potentiation effect was observed during the first training session in either group. Post-activation potentiation appeared in the combined training group during the last training session of the intervention in both 0-10 and 0-30 m sprint. This study illustrates that post-activation potentiation effect on sprint performance in junior basketball players, who did not previously follow systematic resistance training, emerges after a 10-week resistance/sprint combined training programme.
This study examines the biomechanical differences during different vertical jump tasks in 12 prepubescent and 12 adult males. The sagittal knee kinematics, vertical ground reaction force (vGRF) and electromyographic (EMG) activity of 5 lower extremity muscles were recorded. Compared with boys, men presented higher peak vGRF during the propulsive phase in all examined jumps, but lower values during the braking phase, even when related to body mass. Normalized EMG agonist activity in all phases was higher in men (p < .05), while antagonist coactivation was enhanced in boys (p < .05). The knee joint was on average 9 degrees more flexed at touchdown in men during drop jump tasks, but boys exhibited 12 degrees and 17 degrees higher knee flexion at the deepest point when performing drop jump from 20 and 40 cm, respectively. In conclusion, the performance deficit observed in boys in all jump types is a reflection of their immature technique, which could be partly attributed to the less efficient stiffness regulation and activation of their neuromuscular system.
In this study, we examined the interaction between central and peripheral proprioceptive afferent pathways by applying ankle tendon vibration during postural leaning in different directions. Twenty young participants stood for 60s over the midline of two adjacent force platforms in (a) neutral stance distributing Body Weight (BW) equally between the platforms, (b) forward leaning transferring 80% of BW to the front platform and (c) backward leaning transferring 80% of BW to the rear platform. Participants controlled the degree of leaning by receiving on-line visual feedback of BW distribution matched to a target line. Vibration (80Hz, 1.5-1.8mm) was applied over the Achilles or tibialis anterior tendon during the middle 20s of standing. This induced a postural shift towards the vibration side and an increase in the variability of the BW distribution that was greater in backward compared to forward leaning. EMG responses to tendon vibration were independent of the leaning direction. Antagonistic activity also increased in response to vibration, the amplitude of this increase however was direction dependent. These results favor the hypothesis about the central co-modulation of the vibration evoked proprioceptive inflow based on postural and visual feedback rather than muscle tension constraints.
A novel automatic escalator was designed, constructed and used in the present investigation. The aim of the present investigation was to compare the effect of two repeated sessions of stair descending versus stair ascending exercise on muscle performance and health-related parameters in young healthy men. Twenty males participated and were randomly divided into two equal-sized groups: a stair descending group (muscle-damaging group) and a stair ascending group (non-muscle-damaging group). Each group performed two sessions of stair descending or stair ascending exercise on the automatic escalator while a three week period was elapsed between the two exercise sessions. Indices of muscle function, insulin sensitivity, blood lipid profile and redox status were assessed before and immediately after, as well as at day 2 and day 4 after both exercise sessions. It was found that the first bout of stair descending exercise caused muscle damage, induced insulin resistance and oxidative stress as well as affected positively blood lipid profile. However, after the second bout of stair descending exercise the alterations in all parameters were diminished or abolished. On the other hand, the stair ascending exercise induced only minor effects on muscle function and health-related parameters after both exercise bouts. The results of the present investigation indicate that stair descending exercise seems to be a promising way of exercise that can provoke positive effects on blood lipid profile and antioxidant status.
Achilles tendon vibration (ATV) alters proprioceptive input of the triceps surae muscles resulting in a posterior postural shift during standing. When this is applied in combination with a more dynamic proprioceptive perturbation, postural responses to ATV are attenuated. In this study, we applied ATV during self-paced, visually and auditory guided voluntary periodic sway in order to examine how the vibration-induced afferent input is processed and reweighted at the presence of inter-sensory guidance stimuli. Seventeen healthy adults (aged 26.7 ± 4.23 years) performed 15 cycles of periodic sway under three sensory guidance conditions: (a) self-paced, (b) auditory paced (0.25 Hz), and (c) visually driven by matching the resultant force vector to a target sine-wave (0.25 Hz). Bilateral ATV (80 Hz, 3 mm) was applied between the 5th and 10th sway cycles. ATV evoked an earlier burst onset and increased activity of the plantarflexors consistent with a reduction in the amplitude and duration of forward sway. This in turn resulted in an increase in dorsiflexors activity in order to compensate for the greater backward sway. Postural responses to ATV were augmented when sway was auditory and visually guided. Forward sway variability increased with ATV and remained high while backward sway variability decreased in the post-vibration phase. Our results suggest that sensory context-dependent constraints that determine the degree of active control of posture and associated postural challenge involved in a particular task determine how the vibration-induced Ia afferent input will be registered and further processed by the central nervous system.
The purpose of this study was to investigate the effect of a 10-week heavy resistance combined with a running training program on the strength, running speed (RS), and vertical jump performance of young basketball players. Twenty-six junior basketball players were equally divided in 2 groups. The control (CON) group performed only technical preparation and the group that followed the combined training program (CTP) performed additionally 5 sets of 8-5 repetition maximum (RM) half squat with 1 30-m sprint after each set. The evaluation took place before training and after the 5th and 10th weeks of training. Apart from the 1RM half squat test, the 10- and 30-m running time was measured using photocells and the jump height (squat, countermovement jump, and drop jump) was estimated taking into account the flight time. The 1RM increased by 30.3 +/- 1.5% at the 10th week of training for the CTP group (p < 0.05), whereas the CON group showed no significant increase (1.1 +/- 1.6%, p > 0.05). In general, all measured parameters showed a statistically significant increase after the 5th and 10th weeks (p < 0.05), in contrast to the CON group (p > 0.05). This suggests that the applied CTP is beneficial for the strength, RS, and jump height of young basketball players. The observed adaptations in the CTP group could be attributed to learning factors and to a more optimal transfer of the strength gain to running and jumping performance.
The aim of this study was to examine the fatigue and recovery in boys and men during a maximal intermittent isometric fatigue test of the knee extensor muscles, by evaluating the electromyogram of vastus lateralis, vastus medialis and biceps femoris. Thirteen boys (10.0 +/- 0.8yrs) and 13 men (26.1 +/- 4.2yrs) were fatigued until torque reached 50% of its initial value. Three and 6 min after, a maximal isometric knee extension test was assessed. Men had faster torque decline during fatigue and slower torque recovery compared with boys. Agonist activity declined in both groups during fatigue but men had greater extent of reduction. After 6 min boys recovered fully in respect to agonist EMG, whereas this was not the case for the men. The lower level of fatigue and faster recovery in boys could be attributed to the limited inhibition that was observed in the boys agonist muscles, whereas the antagonist activity does not seem to play a role in the fatigue or recovery differences between the groups.
The purpose of the present study was to determine the lower extremities biomechanical differences between prepubescent and adult males during drop jumps (DJs). Twenty-four untrained males (12 prepubescents, 12 adults) performed DJs from 20 cm height. Kinematics of the lower extremities were captured, in addition with vertical ground reaction forces (vGRFs) and EMG activity of the gastrocnemius medialis (GM), soleus (SOL) and tibialis anterior (TA) muscles. The results showed that men jumped higher, as expected, but their knees were more flexed prior to landing, and their preactivation level was higher and longer in duration compared to prepubescent boys. During landing, men had shorter contact times, lower vGRF normalized to body mass, and less maximal knee joint flexion. Regarding EMG activity men presented higher stretch reflex and higher EMG activity during the braking phase but the level of coactivation (TA to GM + SOL ratio) was lower. It is seems that pre-landing and landing patterns during a complex task such as DJ are affected by physical development. There are indications that men had higher performance in a DJ than prepubescent boys because they activated more effectively their muscles during the preactivation and braking phase. The above-mentioned data support the hypothesis that prepubescent boys might be inferior in optimal regulation of their muscle-tendon unit stiffness.
The purpose of the present study was to examine the effect of chronological age and gender on speed development during different sprinting phases in children and adolescents of both genders. The sample consisted of 360 sedentary pupils aged between 7 and 18 years, with 15 pupils representing each subgroup. The 30-m sprint speed was measured with photocells every 10 m. According to the results, boys and girls showed a gradual improvement in running speed during each sprint phase. The 18-year-old boys had significantly higher sprint speed in all measured distances compared to the 15-year-old or younger boys (p < 0.05), whereas the 18-year-old girls had significantly higher speed at the distances of 0 to 10, 10 to 20, 20 to 30, and 0 to 30 m compared to the 13- and 12-year-old or younger girls (p < 0.05). Significant differences between genders in the 15-years-old or older participants were observed. It is concluded that, from 7 to 18 years of age, gender and chronological age are factors that affect running speed during the 30-m sprint. Furthermore, the performance on each sprint phase is uniformly affected by the chronological age. Boys run faster than girls in all running phases, and the span between genders increases after the age of 15 years. It is useful that coaches take these findings into consideration when evaluating children in sprint performance.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.