Quadriceps Muscle Group Research Articles

Does quadriceps neuromuscular activation capability explain walking speed in older men and women?

Age-related impairment of neuromuscular activation has been shown to contribute to weakness in older adults. However, it is unclear to what extent impaired neuromuscular activation independently accounts for decline of mobility function. The hypothesis of this study is that the capability to produce rapid neuromuscular activation during maximal effort leg muscle contractions will be shown to be an independent predictor of mobility function in older men and women after accounting for muscle size and adiposity, body composition and age. Twenty six older men and eighteen older women (aged 70–85years) participated in this study. Mobility function was assessed by the 400-m walk test. Neuromuscular activation of the quadriceps muscle group was assessed by surface electromyography (“rate of EMG rise”). Thigh muscle cross sectional area and adiposity were assessed by computed tomography. In males, univariate regression analysis revealed strong associations between walking speed and a number of predictors including age (p<0.01), muscle area (p<0.01), intermuscular adipose tissue area (p<0.01), and rate of EMG rise (p<0.001). Subsequent multiple regression analysis with all variables accounted for 72% of the variability in walking speed (p<.0001), with age and rate of EMG rise as the dominant variables in the model. In females, univariate analysis showed a significant association only between walking speed and subcutaneous adipose tissue area (p<0.05). Multiple regression analysis accounted for only 44% of the variability in walking speed, and was not statistically significant (p=0.18). The present findings indicate that the capability to rapidly activate the quadriceps muscle group is an important factor accounting for inter-individual variability of walking speed among older men, but not among older women. This research is important for informing the design of assessments and interventions that seek to detect and prevent impairments that contribute to age-related mobility disability.

Different stretching methods of the quadriceps muscles on agility performance in female cricket players of 13-15 years age

Background: Stretching is widely used for various therapeutic purposes, fitness programs, & athletic events. Quondam research shows that stretching may have the pernicious result on performance, therefore precise knowledge of its effects on performance is important to take adequate stretching techniques into consideration for sports training and therapeutic interventions. Need of study: The purpose of our study was to inspect the changes resulting in agility performance from various stretching techniques (static stretching & muscle energy technique) descriptor for the quadriceps muscle group. Method: 60 female cricket players of age 13-15 years were selected to perform the stretching techniques (no stretch, static stretch & muscle energy technique for quadriceps) on three successive days & completed the agility T-test after the three stretching techniques were executed. Result: The mean of agility t-test time were: control group (no stretch) =16.93 seconds, static stretch group=16.3 seconds, muscle energy technique group=16.18 seconds. The test of significance ANOVA shows no statistical significant difference, F=2.8, p=0.05, for the control group (no stretch), static stretching, and muscle energy technique in agility T-test times. Statistical T-test analysis reveals that there is a significant difference between no stretch (control group) and MET group, p-value 0.02 & non-significant difference between no stretch (control group) & static stretch group, p-value 0.057 & static stretch & MET group, p-value 0.72. Conclusion: To conclude, results of our study evince that there is no significant effect on agility after receiving the different stretching techniques with respect to quadriceps muscle.

Reply to “Letter to the editor: ‘Deconstructing the dogma of sympathetic restraint and its role in the cardiovascular response to exercise’”

: We thank Dr. Tschakovsky (3) for his interest andenthusiasm regarding our recent study (1) dealing with sym-pathetic control of blood flow in different tissues of the leg inhumans at rest and during exercise. Dr. Tschakovsky impor-tantly emphasises that exercise-evoked vasodilation cannotdirectly spread from the active quadriceps muscle group to theinactive hamstring muscles. This was not what we literallymeant, and although according to our understanding ascendingvasodilatation and its spread to inactive tissues could be con-tributing to some marginal extent, his concern in this regardwas apparently mainly raised from our integration of ourfindings with those of Moore and colleagues (2), togethersuggesting that -adrenergic-mediated sympathetic constraintis important for optimization of blood flow and oxygen extrac-tion to the most metabolically active tissues of the limb. Wealso fully agree with Dr. Tschakovsky that investigating bloodflow in active versus inactive muscle groups is not the samething as investigating blood flow around active versus inactivemuscle fibers within an exercising muscle. We tried to empha-sise this notion already in the introduction of our paper (1).Regarding the findings from -adrenergic blockade duringexercise, we indeed could not document any change in bloodflow in the exercising muscle. Increased blood flow occurred ininactive muscles and other tissues, indeed very much challeng-ing the common belief that there is sympathetic constraint inthe vasculature of active muscles during exercise, as pointedout by Dr. Tschakovsky (3). Moreover, to the best of ourknowledge, previous research in this area has relied on ratherindirect assessments and estimations. Our study is one of thefirst to directly and quantitatively address this topic in humans.However, as also discussed in the original report (1), we madeour observations during fairly low-intensity exercise, whenalso an only fairly small mass of active muscle was exercising.Thus, even if methodologically quite challenging, it still re-mains to be tested whether the findings are similar at higherexercise intensities and particularly when performing wholebody exercise. In those conditions, it might well be that somesympathetic restraint is needed also in active muscle vascula-ture. At this moment, there is little human experimental evi-dence to support this idea, despite some indirect estimations. Inall, we think that the insightful comments of Dr. Tschakovskywill help vascular and exercise physiologists to better under-stand sympathetic regulation of cardiovascular function duringexercise in humans.

Changes in predicted muscle coordination with subject-specific muscle parameters for individuals after stroke.

Muscle weakness is commonly seen in individuals after stroke, characterized by lower forces during a maximal volitional contraction. Accurate quantification of muscle weakness is paramount when evaluating individual performance and response to after stroke rehabilitation. The objective of this study was to examine the effect of subject-specific muscle force and activation deficits on predicted muscle coordination when using musculoskeletal models for individuals after stroke. Maximum force generating ability and central activation ratio of the paretic plantar flexors, dorsiflexors, and quadriceps muscle groups were obtained using burst superimposition for four individuals after stroke with a range of walking speeds. Two models were created per subject: one with generic and one with subject-specific activation and maximum isometric force parameters. The inclusion of subject-specific muscle data resulted in changes in the model-predicted muscle forces and activations which agree with previously reported compensation patterns and match more closely the timing of electromyography for the plantar flexor and hamstring muscles. This was the first study to create musculoskeletal simulations of individuals after stroke with subject-specific muscle force and activation data. The results of this study suggest that subject-specific muscle force and activation data enhance the ability of musculoskeletal simulations to accurately predict muscle coordination in individuals after stroke.

Estimation of muscle atrophy based on muscle thickness in knee surgery patients

The purpose of this study was to establish an accurate estimation of muscle atrophy in the quadriceps femoris (QF) muscle group. Eighteen individuals who underwent meniscectomy participated in the study (nine men and nine women, mean age 44·4years). Both operated and non-operated thighs were scanned by magnetic resonance imaging to determine the volume and thickness of the QF muscle group. Muscle volume was estimated using eleven axial images, and muscle thickness was measured at the anterior, lateral and medial regions of the proximal, mid- and distal thigh, respectively. A stepwise linear regression analysis was performed to obtain the relationship between the difference in muscle volume and the difference in muscle thickness between operated and non-operated limbs. There was no significant difference in muscle volume of the QF between operated (806·6±220·0cm(3) ) and non-operated (913·7±241·5cm(3) ) limbs. Based on the stepwise linear regression analysis, the difference in muscle volume was significantly correlated with the difference in muscle thickness at the anterior proximal thigh and lateral mid-thigh and anterior mid-thigh (R=0·93, P<0·01). In conclusion, the difference in muscle volume between operated and non-operated limbs can be estimated accurately by measuring muscle thickness of the QF at three sites: the anterior proximal thigh, the lateral mid-thigh and anterior mid-thigh. Muscle thickness can be measured easily using imaging techniques such as ultrasonography. We propose that this method provides an easy and accurate estimate of knee surgery-induced muscle atrophy in clinical medicine.

Interlimb communication to the knee flexors during walking in humans

A strong coordination between the two legs is important for maintaining a symmetric gait pattern and adapting to changes in the external environment. In humans as well as animals, receptors arising from the quadriceps muscle group influence the activation of ipsilateral muscles. Moreover, strong contralateral spinal connections arising from quadriceps and hamstring afferents have been shown in animal models. Therefore, the aims of the present study were to assess if such connections also exist in humans and to elucidate on the possible pathways. Contralateral reflex responses were investigated in the right leg following unexpected unilateral knee joint rotations during locomotion in either the flexion or extension direction. Strong reflex responses in the contralateral biceps femoris (cBF) muscle with a mean onset latency of 76 ± 6 ms were evoked only from ipsilateral knee extension joint rotations in the late stance phase. To investigate the contribution of a transcortical pathway to this response, transcranial magnetic and electrical stimulation were applied. Motor evoked potentials elicited by transcranial magnetic stimulation, but not transcranial electrical stimulation, were facilitated when elicited at the time of the cBF response to a greater extent than the algebraic sum of the cBF reflex and motor evoked potentials elicited separately, indicating that a transcortical pathway probably contributes to this interlimb reflex. The cBF reflex response may therefore be integrated with other sensory input, allowing for responses that are more flexible. We hypothesize that the cBF reflex response may be a preparation of the contralateral leg for early load bearing, slowing the forward progression of the body to maintain dynamic equilibrium during walking.

A Review of the Management of Patellofemoral Pain Syndrome

Objective: Patellofemoral pain syndrome (PFPS) is one of the most frequently diagnosed knee conditions in the primary care, orthopedic, and sports medicine settings. Although strength training and stretching programs have traditionally been the mainstay of patient treatment, there are no consensus recovery protocols for runners experiencing PFPS. The purpose of our review is to examine recent literature regarding the efficacy of various treatment modalities in the management of patients with PFPS. Methods: Our review included 33 articles from a PubMed literature search using the search term PFPS treatment. The search was limited to randomized controlled trials, crossover case-controlled studies, and cohort studies with ⩾ 10 participants, with trial data that were published within the last 5 years. Results: Strength training and stretching exercises continue to be strongly supported by research as effective treatment options for runners with PFPS. Recent studies have confirmed that quadriceps and hip strengthening combined with stretching in a structured physiotherapy program comprise the most effective treatment for reducing knee pain symptoms and improving functionality in patients with PFPS. As previous studies have shown, therapies such as proprioceptive training, orthotics, and taping may offer benefits as adjunctive therapies but do not show a significant benefit when they are used alone in patients with PFPS. Additionally, recent research has confirmed that surgical and pharmacologic therapies are not effective for the management of patients with PFPS. Conclusion: A large number of athletes are impacted by PFPS every year, particularly young runners. Sports medicine researchers have investigated many possible therapies for patients with PFPS; however, no clear guidelines have emerged regarding the management of the syndrome. Our review analyzes recent literature on PFPS and identifies specific treatment recommendations. The most effective and strongly supported treatment modality for patients with PFPS is a combined physiotherapy program, including strength training of the quadriceps and hip abductors and stretching of the quadriceps muscle group. Adjunctive therapies, including taping, biofeedback devices, and prefabricated orthotic inserts, may provide limited additive benefits in select populations. Surgery should be avoided in all patients with PFPS.

Influence of strength training variables on strength gains in adults over 55 years-old: A meta-analysis of dose–response relationships

The importance of strength training to elderly individuals is well established. However, the dose-response relationship of the benefits of strength training in this population is unclear. The purpose of the study was to use meta-analysis to investigate the dose-response of the effects of strength training in elderly individuals. Fifteen studies with a total of 84 effect-sizes were included. The analyses examined the dose-response relationships of the following training variables 'intensity', 'number of sets', 'weekly frequency', and 'training duration' on strength improvement. The studies selected met the following inclusion criteria: (a) randomized controlled trials; (b) trained healthy subjects of both genders; (c) trained subjects aged 55 years or older; (d) strength increases were determined pre- and post-training; (e) use of similar strength evaluation techniques (strength determined by a repetition maximum test) and training routine (dynamic concentric-eccentric knee extension exercise to train the quadriceps muscle group). The effect-sizes were calculated using fixed and random effect models with the main effects determined by meta-regression. Many combinations of training variables resulted in strength increases. However meta-regression indicated only "training duration" had a significant dose-response relationship to strength gains (p=0.001). Over durations of 8-52 weeks, longer training durations had a greater effect on strength gains compared to shorter duration protocols. Resistive training causes strength gains in elderly individuals, provided the training duration is sufficiently long, regardless of the combination of other training variables.

Muscle Functional MRI to Evaluate Quadriceps Dysfunction in Patellofemoral Pain

A dysfunction of the quadriceps muscle group has often been suggested to play an important role in the pathophysiology of patellofemoral pain (PFP). However, consensus is lacking regarding the quadriceps recruitment pattern of patients with PFP. The aim of this study was to examine by muscle functional magnetic resonance imaging if patients with PFP actually exhibit an altered activation of the muscles that play a significant role in the dynamic balance of the patella. Forty-six patients with PFP (25 female and 21 male, mean ± SD age = 25.0 ± 7.4 yr) and 30 healthy control subjects (17 female and 13 male, mean ± SD age = 21.6 ± 4.5 yr) underwent MRI of the quadriceps before and immediately after a squat exercise. The transverse relaxation time (T2) and the T2 shift were calculated for the vasti muscles. There were no significant differences in the T2 values at rest and the T2 shift values between the patient and the control groups, except for the T2 rest value of the VMVI of females (P = 0.007). The T2 shift of the VL was significantly smaller than the T2 shift of the VMVI in both study groups (male P < 0.001 and female P = 0.044), while in females, the T2 shift of the VMO was also significantly smaller than the T2 shift of the VMVI (P = 0.027). The activation pattern of the quadriceps is not altered in patients with PFP for both males and females. Because the relative contribution of the quadriceps muscles to a functional activity has not been modified, there is no evidence for quadriceps dysfunction.

2:42 PM Abstract No. 43 - Embolization of intraosseous AVM

Purpose AVM of bone is a difficult management problem. Because standard embolic agents (glue, PVA, Onyx, Embospheres, etc.) are rarely curative and only palliative, ethanol and ethanol with coils are evaluated to curatively treat bone AVMs. Materials and Methods Twenty-nine patients (17 f, 12 m); age range 6 - 48 years, mean: 19 years) presented with bone AVMs involving the upper extremity, lower extremity, pelvis, spine, and head and neck areas. All patients underwent MR, arteriography, and endovascular repair of their bone AVMs. Ethanol alone and ethanol with coils were the sole embolic agents. Results Twenty-eight of twenty-nine patients are cured of their intraosseous AVM at follow-up (range 8 months - 120 months; mean: 42 months). One patient’s therapy is on-going (mandible/maxilla/face AVMs). Complications include one coil migration to the lung (retrieved without sequelae), three patients with skin injury in the lower extremity (healed uneventfully), and one patient with chronic weakness left quadriceps femoris muscle group, which was present prior to treatment and not improved with treatment of her pelvic/iliac wing AVM. Conclusion Bone AVMs in the literature are rarely cured, save by amputation. Ethanol or ethanol with coils has proven to be consistent in ablating bone AVMs and durable at long-term follow-up, in essence curing the AVM. When bone AVM is present in an extremity, multiple AVMs in that extremity can occur. Acceptable low complication rates are noted in this series.

Morphological and Physiological Profile of Elite Basketball Players in Belgium

The current study aimed to gain insight into the physiological profile of elite basketball players in Belgium in relation to their position on the field. The group consisted of 144 players, divided into 5 groups according to position (point guards [PGs], shooting guards [SGs], small forwards [SFs], power forwards [PFs], and centers [Cs]). The anthropometrics were measured and the subjects underwent fitness tests (incremental running test, 10-m sprint, 5 ×-10 m, squat and countermovement jump, isokinetic test) to obtain insight into endurance, speed, agility, and power. The parameters of these tests were compared among the different positions by means of 1-way variance analysis (MANOVA). Tukey post hoc tests were performed in case of a significant MANOVA. It was observed that Cs were taller and heavier and had a higher percentage body fat than PGs and SGs. For the anaerobic sprint test Cs were slower than the other positions. For the 5 × 10-m the PGs and SGs were faster than SFs and PFs. For the jump test Cs displayed a significantly lower absolute performance than the other positions. PGs and SGs had a higher VO(2peak) and speed at the anaerobic threshold than PFs and Cs. The isokinetic strength test showed that the quadriceps muscle group of Cs could exert a higher torque during knee extension than the other positions. The current study showed that the physiological profile of elite players in the Belgian first division differs by player position. More specifically, guards were characterized by high endurance, speed, and agility, whereas centers and power forwards had higher muscle strength than the other positions.

Regional differences in blood flow, glucose uptake and fatty acid uptake within quadriceps femoris muscle during dynamic knee-extension exercise

The purpose of the present study was to investigate the regional differences in glucose and fatty acid uptake within skeletal muscle during exercise. Blood flow (BF), glucose uptake (GU) and free fatty acid uptake (FFAU) were measured in four different regions (vastus lateralis, VL; rectus femoris, RF; vastus intermedius, VI; and vastus medialis, VM) of the quadriceps femoris (QF) muscle during low-intensity, knee-extension exercise using positron emission tomography. BF was higher in VI than in VL, RF and VM (P < 0.05). FFAU was higher in VI (P < 0.001) but also in VM (P < 0.05) compared with VL and RF. In contrast, GU was higher in RF compared with VL (P < 0.05) but was not significantly different to VM or VI (both P = NS). FFAU within these four muscle regions correlated significantly with BF (r = 0.951, P < 0.05), whereas no significant relationship was observed between GU and BF (r = 0.352, P = NS). Therefore, skeletal muscle FFAU, but not GU, appears to be associated with BF during low-intensity exercise. The present results also indicate considerable regional differences in substrate use within working QF muscle. As such, an important methodological outcome from these results is that one sample from a specific part of the QF muscle does not represent the response in the entire QF muscle group.

Ant Colony Optimization Tuning PID Algorithm for Precision Control of Functional Electrical Stimulation

Functional electrical stimulation (FES) can restore motor function in individuals with spinal cord injury (SCI). Neuroprostheses based on FES apply electric stimuli to induce muscle contractions and the corresponding joint movements. The goal of this study was to design a novel FES controller, and the attention is focused on the feedback control of the knee-joint movements induced by electrical stimulation of the quadriceps muscle group. Ant colony optimization algorithm is employed to modulate the propor- tional, integral and derivative values of PID controller. The promising results showed the ACO-PID controller func- tioned as expected and performed better than the GA-PID controller. This method for a knee-joint movement resulted in decrease of the tracking error and shortened delay in the response, which may be applied in walking-assisted FES.

Traumatic fibrotic myopathy of the tensor fascia lata muscle in a Whippet

A two-year-old female neutered Whippet was referred for evaluation of progressive right pelvic limb lameness. Clinical examination revealed a fibrous band palpable along the cranial aspect of the quadriceps muscle group, and signs of discomfort on extension of the right hip. Computed tomography and ultrasonographic examination revealed mineralization of the tensor fascia lata muscle with enthesophytosis of its origin. Surgical exploration confirmed a fibrous band affecting the cranial border of the tensor fascia lata muscle. Resection of the band resulted in complete resolution of clinical signs. Histopathology was consistent with a fibrotic myopathy. To the authors' knowledge, this is the first case of a fibrotic myopathy affecting the tensor fascia lata muscle in the dog.

Increasing Exercise Intensity Reduces Heterogeneity of Glucose Uptake in Human Skeletal Muscles

Proper muscle activation is a key feature of survival in different tasks in daily life as well as sports performance, but can be impaired in elderly and in diseases. Therefore it is also clinically important to better understand the phenomenon that can be elucidated in humans non-invasively by positron emission tomography (PET) with measurements of spatial heterogeneity of glucose uptake within and among muscles during exercise. We studied six healthy young men during 35 minutes of cycling at relative intensities of 30% (low), 55% (moderate), and 75% (high) of maximal oxygen consumption on three separate days. Glucose uptake in the quadriceps femoris muscle group (QF), the main force producing muscle group in recreational cycling, and its four individual muscles, was directly measured using PET and 18F-fluoro-deoxy-glucose. Within-muscle heterogeneity was determined by calculating the coefficient of variance (CV) of glucose uptake in PET image voxels within the muscle of interest, and among-muscles heterogeneity of glucose uptake in QF was expressed as CV of the mean glucose uptake values of its separate muscles. With increasing intensity, within-muscle heterogeneity decreased in the entire QF as well as within its all four individual parts. Among-muscles glucose uptake heterogeneity also decreased with increasing intensity. However, mean glucose uptake was consistently lower and heterogeneity higher in rectus femoris muscle that is known to consist of the highest percentage of fast twitch type II fibers, compared to the other three QF muscles. In conclusion, these results show that in addition to increased contribution of distinct muscle parts, with increases in exercise intensity there is also an enhanced recruitment of muscle fibers within all of the four heads of QF, despite established differences in muscle-part specific fiber type distributions. Glucose uptake heterogeneity may serve as a useful non-invasive tool to elucidate muscle activation in aging and diseased populations.

Prior Eccentric Exercise Reduces V[Combining Dot Above]O2peak and Ventilatory Threshold but Does Not Alter Movement Economy During Cycling Exercise

Exercise-induced muscle damage (EIMD) has been shown to reduce force production and result in delayed-onset soreness and pain in the damaged muscle(s). Cycling in the presence of EIMD reduces peak power output and time-trial performance. However, its effect on peak aerobic capacity has not been widely studied. The purpose of this study was to examine the impact of EIMD targeted specifically to the quadriceps muscle group on peak oxygen consumption (V[Combining Dot Above]O2peak) during cycling. Ten participants (4 men, 6 women) completed a V[Combining Dot Above]O2peak test on a cycle ergometer before and 48 hours after performing 24 eccentric contractions with their right and left quadriceps with a weight equal to 120% of 1-repetition maximal concentric strength (1RM). The EIMD was assessed using 1RM, and muscle soreness was assessed using a 100-mm visual analog scale. The presence of EIMD was confirmed by a 9% reduction in 1RM (p = 0.0001) and increased ratings of soreness from 2.4 ± 2.1 to 24.6 ± 10.8 mm (p = 0.001). The V[Combining Dot Above]O2peak was reduced from 46.2 ± 9.7 to 41.8 ± 10.7 ml·kg·min (10%; p = 0.01) with participants terminating exercise at lower heart rates 191 ± 9 vs. 186 ± 10 b·min (p = 0.02) and power output 248 ± 79 vs. 238 ± 81 W (p = 0.02) after EIMD. Additionally, ventilatory threshold decreased from 34.2 ± 7.8 to 30.5 ± 8.5 ml·kg·min (11%; p = 0.031). Despite the reduction in V[Combining Dot Above]O2peak, cycling economy (p = 0.17) did not differ pre-EIMD and post-EIMD. These findings indicate that EIMD reduced peak aerobic exercise capacity to an extent that could result in meaningful reductions in exercise performance. The reduction is likely attributable to a combination of reduced strength, earlier accumulation of lactic acid, and heightened muscle pain during exercise.

Surface electromyography reveals males have a slower patellar reflex than females

In humans the cross sectional area of spinal motor neurons at L3 is larger in males than in females. Since these contribute to the control of the quadriceps femoris muscle group and are involved in the patellar reflex (PR), gender differences in the PR are expected. We have investigated this possibility using a group of 28 young subjects (14 male and 14 female) aged 20–22years. The PR was quantified by the muscle compound action potential (MCAP) from the surface electromyogram (sEMG) of the vastus lateralis muscle. We found that the PR latency in females (17±0.19ms), was significantly (p<0.001) faster than in males (21±0.37ms). This 4ms difference in latency could not be ascribed to differences in stature or thigh length. In conclusion, for the age range tested females posses a significantly faster patellar reflex than males. We suggest that the slower PR latency of male subjects may arise in part from their larger α-motorneurons: such that longer integration times are required for the summation of postsynaptic excitation to be sufficient to excite α-motorneurons.

6주간 야외용 운동기구를 사용한 저항운동이 노인 여성의 무릎신전근 기능 및 구조에 미치는 영향

The purpose of this study was to investigate the effect of leg extension exercises performed on outdoor resistance exercise machines on knee extension muscle strength and quadriceps muscle group cross sectional area (CSA) in elderly women. Two groups were recruited for this study, including an exercise group (EG: n=13, <TEX>$71.38{\pm}2.79$</TEX> yrs) and a control group (CG: n=5, <TEX>$73.4{\pm}5.94$</TEX>), In all subjects, maximum isometric and isokinetic muscle strength of knee flexion and extension were measured using an isokinetic dynamometer (Cybex(R) Humac Norm Testing & Rehabilitation System, USA). Quadriceps muscle group CSA were measured using MRI (Philps, Intera 1.5 T, NE Netherlands). The results of this study showed that post-intervention isometric knee extension peak torque value were higher than pre-intervention measures in the EG. However, the EG did not show improvement in quadriceps muscle group CSA, Also, no differences in the shift of optimal knee joint angle were observed between pre and post-intervention exercise. Outdoor leg extension exercise showed small increases in muscle strength in comparison to other resistance training exercises. The results of this study suggest that because outdoor leg extension exercise machines lack a progressive loading mechanism, significant increases in muscle strength may not be obtained.

Closed-Loop Neural Network-Based NMES Control for Human Limb Tracking

Closed-loop control of skeletal muscle is complicated by the nonlinear muscle force to length and velocity relationships and the inherent unstructured and time-varying uncertainties in available models. Some pure feedback methods have been developed with some success, but the most promising and popular control methods for neuromuscular electrical stimulation (NMES) are neural network (NN)-based methods. Efforts in this paper focus on the use of a NN feedforward controller that is augmented with a continuous robust feedback term to yield an asymptotic result (in lieu of typical uniformly ultimately bounded stability). Specifically, an NN-based controller and Lyapunov-based stability analysis are provided to enable semi-global asymptotic tracking of a desired limb time-varying trajectory (i.e., non-isometric contractions). The developed controller is applied as an amplitude modulated voltage to external electrodes attached to the distal-medial and proximal-lateral portion of the quadriceps femoris muscle group in non-impaired volunteers. The added value of incorporating a NN feedforward term is illustrated through experiments that compare the developed controller with and without the NN feedforward component.

A Comparison of the Effects of 6 Weeks of Traditional Resistance Training, Plyometric Training, and Complex Training on Measures of Strength and Anthropometrics

Complex training (CT; alternating between heavy and lighter load resistance exercises with similar movement patterns within an exercise session) is a form of training that may potentially bring about a state of postactivation potentiation, resulting in increased dynamic power (Pmax) and rate of force development during the lighter load exercise. Such a method may be more effective than either modality, independently for developing strength. The purpose of this research was to compare the effects of resistance training (RT), plyometric training (PT), and CT on lower body strength and anthropometrics. Thirty recreationally trained college-aged men were trained using 1 of 3 methods: resistance, plyometric, or complex twice weekly for 6 weeks. The participants were tested pre, mid, and post to assess back squat strength, Romanian dead lift (RDL) strength, standing calf raise (SCR) strength, quadriceps girth, triceps surae girth, body mass, and body fat percentage. Diet was not controlled during this study. Statistical measures revealed a significant increase for squat strength (p = 0.000), RDL strength (p = 0.000), and SCR strength (p = 0.000) for all groups pre to post, with no differences between groups. There was also a main effect for time for girth measures of the quadriceps muscle group (p = 0.001), the triceps surae muscle group (p = 0.001), and body mass (p = 0.001; post hoc revealed no significant difference). There were main effects for time and group × time interactions for fat-free mass % (RT: p = 0.031; PT: p = 0.000). The results suggest that CT mirrors benefits seen with traditional RT or PT. Moreover, CT revealed no decrement in strength and anthropometric values and appears to be a viable training modality.