Acute effects of conventional versus wide-pulse neuromuscular electrical stimulation on quadriceps evoked torque and neuromuscular function.

PURPOSE: The effectiveness of a neuromuscular electrical stimulation (NMES) program is proportional to the level of evoked torque, which can be achieved with either conventional or wide-pulse stimulations. The aim of this study was to compare evoked torque, objective fatigability, and related peripheral and central alterations, as well as changes in central nervous system (CNS) excitability induced by an acute session of conventional versus wide-pulse NMES. METHODS: Seventeen young men underwent three 20-min NMES sessions: conventional (0.2 ms/50 Hz), wide-pulse at 50 Hz (1 ms/50 Hz), and wide-pulse at 100 Hz (1 ms/100 Hz). Neuromuscular measurements (i.e., maximal voluntary contraction, voluntary activation, evoked responses to femoral nerve stimulation, and CNS excitability) were performed on the right quadriceps femoris muscle before and after each NMES session. CNS excitability was measured using transcranial magnetic, thoracic, and transcutaneous spinal cord stimulations. RESULTS: The level of evoked torque was not significantly different between conventional and wide-pulse protocols applied at the maximal tolerable current intensity. All NMES protocols induced objective fatigability (~14% decrease in maximal voluntary contraction torque, p < 0.001) associated with peripheral (decrease in doublet torque and potentiated M-wave amplitude, p = 0.002 and p < 0.001, respectively) but not central (unchanged voluntary activation, p = 0.79) alterations. However, these acute changes did not differ between NMES protocols and none of the NMES protocols modified markers of CNS excitability. CONCLUSION: These results may allow to conjecture that chronic effects and treatment effectiveness could be comparable between conventional and wide-pulse NMES.

Wide-pulse electrical stimulation of the quadriceps allows greater maximal evocable torque than conventional stimulation.

PURPOSE: The effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequencies. METHODS: MET-expressed as a percentage of maximal voluntary contraction (MVC) torque-and maximal tolerable current intensity were quantified on 71 healthy subjects. The right quadriceps was stimulated with three NMES protocols using different pulse duration/frequency combinations: conventional NMES (0.2 ms/50 Hz; CONV), wide-pulse NMES at 50 Hz (1 ms/50 Hz; WP50) and wide-pulse NMES at 100 Hz (1 ms/100 Hz; WP100). The proportion of subjects reaching the maximal stimulator output (100 mA) before attaining maximal tolerable current intensity was also quantified. RESULTS: The proportion of subjects attaining maximal stimulator output was higher for CONV than WP50 and WP100 (p < 0.001). In subjects who did not attain maximal stimulator output in any protocol, MET was higher for both WP50 and WP100 than for CONV (p < 0.001). Maximal tolerable current intensity was lower for both WP50 and WP100 than for CONV and was also lower for WP100 than for WP50 (p < 0.001). CONCLUSION: When compared to conventional NMES, wide-pulse protocols resulted in greater MET and lower maximal tolerable current intensity. Overall, this may lead to better NMES training/rehabilitation effectiveness and less practical issues associated with maximal stimulator output limitations.

Non-inferiority of a home-based videoconference physical training program in comparison with the same program administered face-to-face in healthy older adults: the MOTION randomised controlled trial.

BACKGROUND: older adults often fail to reach the recommended amount of physical activity to prevent the age-related decline in metabolic, cardiorespiratory and muscular function. Effective home-based physical training programs could neutralise barriers preventing older adults from being active, and administration/supervision through videoconference may be an optimal solution. The present randomised controlled trial aimed to test the non-inferiority of training program administered through videoconference against the same program administered face-to-face in healthy older adults. METHODS: participants were randomised in a no-training control group (n = 13), a face-to-face training group (n = 15) and a videoconference training group (n = 13). The intervention groups completed the same home-based, structured, progressive and combined training program for 16 weeks, 1-h twice a week. Pre-intervention and post-intervention evaluations included body composition, cardiorespiratory fitness and muscle function measures. RESULTS: non-inferiority of videoconferencing against face-to-face training was observed for changes in body weight (P < 0.01), fat mass (P = 0.015), maximal aerobic power (P = 0.013), maximal heart rate (P = 0.034), maximal oxygen consumption (P < 0.01), knee extension strength (P = 0.044) and lower limb power (P = 0.019), but not for muscle mass (P = 0.067), handgrip strength (P = 0.171), trunk extension strength (P = 0.241) and knee flexion strength (P = 0.462). CONCLUSION: a training program administered through videoconferencing was not inferior to the same program administered face-to-face for reducing body weight and fat mass, and for improving maximal aerobic power and oxygen consumption as well as lower limb power and knee extension strength in healthy older subjects. However, videoconferencing training was not as effective as face-to-face training for improving handgrip, trunk extension and knee flexion isometric strength.

Peripheral muscle function during repeated changes of direction in professional soccer players.

PURPOSES: To evaluate peripheral muscle function of the knee extensors during repeated changes of direction in professional soccer players by examining differences between competitive levels, periods of the season and playing positions, and to investigate the relationships between peripheral muscle function and physical activities during matches. METHODS: Knee extensor peripheral muscle function (twitch peak torque, PT) of 593 male soccer players from 13 European professional clubs competing at 3 different levels was evaluated 4 times during the season. The main outcomes were PTmax (maximal PT, muscle contractility), MPmax (maximal metabolic power exercise intensity) and PTdec (PT decline, muscle fatigability) obtained during intermittent runs of increasing intensity with multiple changes of direction interspersed with electrically evoked contractions. Relative total and sprint distances covered during a whole match and during short intervals were quantified from a sub-sample. RESULTS: PTmax and MPmax were higher for first than for second division (p < 0.047; d = 0.15-0.23) and Under-19 players (p < 0.007; d = 0.17-0.25). MPmax was lower (p < 0.016; d = 0.23-0.32) and PTdec was higher (p < 0.004; d = 0.26-0.39) in the pre-season compared to all the other time points. MPmax was higher for fullbacks than attackers and defenders (p < 0.041; d = 0.20-0.22). PTdec was higher for defenders than fullbacks, midfielders and wings (p < 0.029; d = 0.21-0.28). PTmax was associated with whole-match relative total distance (p = 0.004; d = 0.26). PTdec was associated with whole-match relative total distance and relative short-interval sprint distance (p < 0.050; d = 0.18-0.22). CONCLUSION: The ability to sustain repeated change of direction efforts at high intensities while preserving peripheral muscle function should be considered an important determinant of soccer physical performance.

Enhancing Adaptations to Neuromuscular Electrical Stimulation Training Interventions.

Neuromuscular electrical stimulation (NMES) applied to skeletal muscles is an effective rehabilitation and exercise training modality. However, the relatively low muscle force and rapid muscle fatigue induced by NMES limit the stimulus provided to the neuromuscular system and subsequent adaptations. We hypothesize that adaptations to NMES will be enhanced by the use of specific stimulation protocols and adjuvant interventions.

Daily 30-min exposure to artificial gravity during 60 days of bed rest does not maintain aerobic exercise capacity but mitigates some deteriorations of muscle function: results from the AGBRESA RCT.

PURPOSE: Spaceflight impairs physical capacity. Here we assessed the protective effect of artificial gravity (AG) on aerobic exercise capacity and muscle function during bed rest, a spaceflight analogue. METHODS: 24 participants (33 ± 9 years, 175 ± 9 cm, 74 ± 10 kg, 8 women) were randomly allocated to one of three groups: continuous AG (cAG), intermittent AG (iAG) or control (CTRL). All participants were subjected to 60 days of six-degree head-down tilt bed rest, and subjects of the intervention groups completed 30 min of centrifugation per day: cAG continuously and iAG for 6 × 5 min, with an acceleration of 1g at the center of mass. Physical capacity was assessed before and after bed rest via maximal voluntary contractions, cycling spiroergometry, and countermovement jumps. RESULTS: AG had no significant effect on aerobic exercise capacity, flexor muscle function and isometric knee extension strength or rate of force development (RFD). However, AG mitigated the effects of bed rest on jumping power (group * time interaction of the rmANOVA p < 0.001; iAG - 25%, cAG - 26%, CTRL - 33%), plantar flexion strength (group * time p = 0.003; iAG - 35%, cAG - 31%, CTRL - 48%) and plantar flexion RFD (group * time p = 0.020; iAG - 28%, cAG - 12%, CTRL - 40%). Women showed more pronounced losses than men in jumping power (p < 0.001) and knee extension strength (p = 0.010). CONCLUSION: The AG protocols were not suitable to maintain aerobic exercise capacity, probably due to the very low cardiorespiratory demand of this intervention. However, they mitigated some losses in muscle function, potentially due to the low-intensity muscle contractions during centrifugation used to avoid presyncope.

Impact of COVID-19 Lockdown on Serie A Soccer Players' Physical Qualities.

In March 2020, the COVID-19 pandemic forced most activities in Italy, including soccer, to cease. During lockdown, players could only train at home, with limited evidence regarding the effect of this period. Therefore, this study aimed to investigate the effect of COVID-19 lockdown on professional soccer players' physical performance. Aerobic fitness and vertical jump were assessed before and after four periods in two different seasons: COVID-19 lockdown, competitive period before lockdown, competitive period and summer break of the 2016-2017 season. Linear mixed models were used to examine within-period changes and between-period differences in changes observed during COVID-19 lockdown and the three other periods. Within-period changes in aerobic fitness showed a significant improvement following COVID-19 lockdown (p<0.001) and a significant decline during summer break (p<0.001). Between-period differences were significant in the comparison of COVID-19 lockdown with both the competitive 2019-2020 season (p<0.01) and summer break (p<0.001). For the vertical jump, only the between-period comparison revealed significant differences as the changes associated with COVID-19 lockdown were worse than those of the two competitive periods, for both absolute (p<0.05; p<0.001) and relative peak power (p<0.01; p<0.001). Home-based training during lockdown was effective to improve aerobic fitness, although it did not allow players to maintain their competitive period's power levels.

Perceived Barriers to and Facilitators of an Injury Prevention Program Among Professional Male Ice Hockey Players and Staff Members.

CONTEXT: Injury prevention programs for the lower extremities are effective in team-sport athletes. OBJECTIVE: To identify barriers and facilitators among professional ice hockey players and staff members for adhering to an injury prevention program. DESIGN: Cross-sectional survey. SETTING AND PARTICIPANTS: A questionnaire about barriers and facilitators related to knowledge/perceptions, beliefs, adoption, and habits about injury prevention was filled out by Swiss professional male ice hockey players and staff members. MAIN OUTCOME MEASURES: Frequencies of ratings were calculated and binary logistic regression analysis was applied to predict a relationship between a high/low perceived benefit of an injury prevention program and player characteristics. RESULTS: Knowledge, perceived benefit, and relevance of injury prevention as well as awareness of high risk of injuries in ice hockey were identified as important facilitators. Players' habit of exercise performance was identified as a barrier. Program understanding of staff members was identified as a facilitator and barrier. No significant relationships were observed between a high/low perceived benefit of an injury prevention program and age (P = .85), nationality (P = .53), level of education (P = .63), National League experience (P = .50), or occurrence of lower-extremity injuries in the previous season (P = .10). CONCLUSIONS: Players and staff members clearly rated perceived benefits of an injury prevention program, which can be considered an important facilitator of the uptake and adoption of such a program in ice hockey teams. Players should be educated about well-performed injury prevention exercises. Staff members should be educated about the aim of a regular injury prevention program. An injury prevention program might be implemented in players of all ages, levels of education, and experience in the National League, irrespective of previous injuries. Identified barriers and facilitators should be addressed when implementing an injury prevention program in a setting of professional ice hockey teams in the future.

Obesity-associated poor muscle quality: prevalence and association with age, sex, and body mass index.

BACKGROUND: Muscle quality (i.e., the expression of muscle function per unit of muscle mass) has been proposed as a clinically-relevant measure to detect individuals at risk of functional incapacity. Individuals with obesity might be at an increased risk of having poor muscle quality. Thus, we aimed to analyze the prevalence of poor muscle quality in obese individuals, to determine associated variables, and to provide normative values for this population. METHODS: 203 individuals with obesity (103 women, age: 18-75 years, body mass index (BMI): 35-64 kg·m- 2) participated in this cross-sectional study. Their muscle strength (handgrip dynamometry), muscle power (sit-to-stand test) and muscle mass (bioelectrical impedance analysis) were measured, and muscle quality (strength/power to muscle mass ratio) was compared with reference values obtained in young healthy individuals. Muscle quality was individually categorized as normal, low or poor based on specific muscle strength and power (i.e., strength and power per unit of muscle mass, respectively). Sex and age-specific normative values of specific muscle strength and power were computed for the whole cohort. RESULTS: Age and being a woman were inversely associated with specific muscle strength, with age being also inversely associated with specific muscle power. A small proportion of participants (6%) presented with an impaired (i.e., low/poor) specific muscle power while most of them (96%) had impaired specific muscle strength. Eventually, 84% of the participants were deemed to have poor muscle quality. Being a woman (odds ratio [OR]: 18.09, 95% confidence intervals [CI]: 4.07-80.38), age (OR: 1.06, 95%CI: 1.03-1.10) and BMI (OR: 1.22, 95%CI: 1.07-1.38) were independently associated with a higher risk of poor muscle quality in adjusted analyses. CONCLUSIONS: These findings show a high prevalence of poor muscle quality among individuals with obesity, with age, sex and BMI being independent predictors.

Neuromuscular adaptations to wide-pulse high-frequency neuromuscular electrical stimulation training.

PURPOSE: No studies have evaluated the potential benefits of wide-pulse high-frequency (WPHF) neuromuscular electrical stimulation (NMES) despite it being an interesting alternative to conventional NMES. Hence, this study evaluated neuromuscular adaptations induced by 3 weeks of WPHF NMES. METHODS: Ten young healthy individuals (training group) completed nine sessions of WPHF NMES training spread over 3 weeks, whereas seven individuals (control group) only performed the first and last sessions. Plantar flexor neuromuscular function (maximal voluntary contraction (MVC) force, voluntary activation level, H reflex, V wave, contractile properties) was evaluated before the first and last training sessions. Each training session consisted of ten 20-s WPHF NMES contractions (pulse duration: 1 ms, stimulation frequency: 100 Hz) interspaced by 40 s of recovery and delivered at an intensity set to initially evoke ~ 5% of MVC force. The averaged mean evoked forces produced during the ten WPHF NMES-evoked contractions of a given session as well as the sum of the ten contractions force time integral (total FTI) were computed. RESULTS: Total FTI (+ 118 ± 98%) and averaged mean evoked forces (+ 96 ± 91%) increased following the 3-week intervention (p < 0.05); no changes were observed in the control group. The intervention did not induce any change (p > 0.05) in parameters used to characterize plantar flexor neuromuscular function. CONCLUSION: Three weeks of WPHF NMES increased electrically evoked forces but induced no other changes in plantar flexor neuromuscular properties. Before introducing WPHF NMES clinically, optimal training program characteristics (such as frequency, duration and intensity) remain to be identified.

Effectiveness of multicomponent lower extremity injury prevention programmes in team-sport athletes: an umbrella review.

OBJECTIVE: To identify which exercise combinations are most effective as part of a lower extremity injury prevention programme for team-sport athletes. DESIGN: Umbrella review. DATA SOURCES: A comprehensive literature search was performed in PubMed, Scopus, Cochrane Library and PEDro databases. Studies published between January 2000 and March 2017 were included in this umbrella review. STUDY ELIGIBILITY CRITERIA: Moderate to high-quality systematic reviews that investigated the effectiveness of a combination of two or more exercise components, that is, strength, agility, plyometrics, balance, stretching, technique, warm-up and functional activity, regarding injury incidence/rate of lower extremity injuries in team-sport athletes. The methodological quality of the included systematic reviews was independently assessed by two reviewers using the Assessing the Methodological Quality of Systematic Reviews measurement tool and the Grading of Recommendations Assessment, Development and Evaluation guidelines were used to assess the overall quality of evidence for particular outcomes. RESULTS: Twenty-four systematic reviews met the inclusion criteria. Multicomponent exercise interventions were effective in reducing the injury incidence/rate of lower extremity, knee, ACL and ankle injuries, but not groin injuries. Strength and balance exercise components were included in 10 of 11 effective injury prevention programmes for the lower extremity, knee, ACL and ankle injuries. SUMMARY/CONCLUSION: Lower extremity injury prevention programmes in team sports are effective in preventing lower extremity, knee, ACL and ankle injuries. Lower extremity muscle strength and balance exercises should be prioritised in lower extremity injury prevention programmes for team-sport athletes.

Effect of milking stall dimensions on upper limb and shoulder muscle activity in milkers.

Increasing societal awareness for animal welfare can promote changes in legislation. Some of these changes may also affect the person that interacts with the animal in a shared workspace, such as in milking stalls. Swiss milking stalls were designed many years ago, when cows were smaller than they are today. A recent animal-based study indicated that welfare decreased in cows exposed to restricted space allowance in milking stalls, which had resulted from increasing body size without adjustment of milking stall dimensions. However, changing the milking stall dimensions without considering the milker may be detrimental. For many years, health issues, particularly of the upper limb and shoulders, have affected milking personnel. The current study investigated the effect of large and standard milking stall dimensions on muscle activity in milkers (as a measure of workload) during milking. This assessment is fundamental to ensure that legislation improving animal welfare does not jeopardize human health. The study took place in an experimental milking parlor that allowed for size adjustment of the individual milking stall. Nine milkers performed 2 shifts of milking in a herringbone and 2 shifts in a side-by-side milking parlor. The milking stall dimensions were large on one side and standard on the other side of the parlor; the 2 sides were switched between milking shifts. We used surface electromyography to monitor bilateral muscle activity of forearm (flexor carpi ulnaris), arm (biceps brachii), and shoulder (deltoideus anterior; upper trapezius) muscles. Statistical analysis was performed separately for the herringbone and the side-by-side parlor for each muscle using mean and maximum muscle activity as the target variables in a linear mixed-effects model. The analysis showed that the different milking stall dimensions did not consistently affect activity of the measured muscles. Our results suggest that milking stall dimensions are not a primary risk factor for poor ergonomics in parlor workers.

Somatosensory electrical stimulation improves skill acquisition, consolidation, and transfer by increasing sensorimotor activity and connectivity.

The interaction between the somatosensory and motor systems is important for normal human motor function and learning. Enhancing somatosensory input using somatosensory electrical stimulation (SES) can increase motor performance, but the neuronal mechanisms underlying these effects are largely unknown. With EEG, we examined whether skill acquisition, consolidation, and interlimb transfer after SES was related to increased activity in sensorimotor regions, as assessed by the N30 somatosensory evoked potential or rather increased connectivity between these regions, as assessed by the phase slope index (PSI). Right- and left-hand motor performance and EEG measures were taken before, immediately after, and 24 h ( day 2) after either SES ( n = 12; 5 men) or Control ( n = 12; 5 men). The results showed skill acquisition and consolidation in the stimulated right hand immediately after SES (6%) and on day 2 (9%) and interlimb transfer to the nonstimulated left hand on day 2 relative to Control (8%, all P < 0.05). Increases in N30 amplitudes correlated with skill acquisition while PSI from electrodes that represent the posterior parietal and primary somatosensory cortex to the electrode representing the primary motor cortex correlated with skill consolidation. In contrast, interlimb transfer did not correlate with the EEG-derived neurophysiological estimates obtained in the present study, which may indicate the involvement of subcortical structures in interlimb transfer after SES. In conclusion, weak peripheral somatosensory inputs in the form of SES improve skill acquisition, consolidation, and interlimb transfer that coincide with different cortical adaptations, including enhanced N30 amplitudes and PSI. NEW & NOTEWORTHY The relationship between adaptations in synaptic plasticity and motor learning following somatosensory electrical stimulation (SES) is incompletely understood. Here, we used for the first time a multifactorial approach that examined skill acquisition, consolidation, and interlimb transfer following 20 min of SES. In addition, we quantified sensorimotor integration and the magnitude and direction of connectivity with EEG. Following artificial electrical stimulation, increases in sensorimotor integration and connectivity were found to correlate with skill acquisition and consolidation, respectively.

Clinical Use of Neuromuscular Electrical Stimulation for Neuromuscular Rehabilitation: What Are We Overlooking?

The clinical success of neuromuscular electrical stimulation (NMES) for neuromuscular rehabilitation is greatly compromised by the poor consideration of different physiological and methodological issues that are not always obvious to the clinicians. Therefore, the aim of this narrative review is to reexamine some of these fundamental aspects of NMES using a tripartite model perspective. First, we contend that NMES does not actually bypass the central nervous system but results in a multitude of neurally mediated responses that contribute substantially to force generation and may engender neural adaptations. Second, we argue that too much emphasis is generally placed on externally controllable stimulation parameters while the major determinant of NMES effectiveness is the intrinsically determined muscle tension generated by the current (ie, evoked force). Third, we believe that a more systematic approach to NMES therapy is required in the clinic and this implies a better identification of the patient-specific impairment and of the potential "responders" to NMES therapy. On the basis of these considerations, we suggest that the crucial steps to ensure the clinical effectiveness of NMES treatment should consist of (1) identifying the neuromuscular impairment with clinical assessment and (2) implementing algorithm-based NMES therapy while (3) properly dosing the treatment with tension-controlled NMES and eventually amplifying its neural effects.

Short vs. long pulses for testing knee extensor neuromuscular properties: does it matter?

PURPOSE: The present study aimed at comparing knee extensor neuromuscular properties determined with transcutaneous electrical stimulation using two pulse durations before and after a standardized fatigue protocol. METHODS: In the first sub-study, 19 healthy participants (ten women and nine men; 28 ± 5 years) took part to two separate testing sessions involving the characterization of voluntary activation (twitch interpolation technique), muscle contractility (evoked forces by single and paired stimuli), and neuromuscular propagation (M-wave amplitude from vastus lateralis and vastus medialis muscles) obtained at supramaximal intensity with a pulse duration of either 0.2 or 1 ms. The procedures were identical in the second sub-study (N = 11), except that neuromuscular properties were also evaluated after a standardized fatiguing exercise. Electrical stimulation was delivered through large surface electrodes positioned over the quadriceps muscle and a visual analog scale was used to evaluate the discomfort to paired stimuli evoked at rest. RESULTS: There was no difference between pulse durations in the estimates of voluntary activation, neuromuscular propagation, and muscle contractility both in the non-fatigued and fatigued states. The discomfort associated with supramaximal paired electrical stimuli was also comparable between the two pulse durations. CONCLUSIONS: It appears that 0.2- and 1-ms-long pulses provide a comparable evaluation of knee extensor neuromuscular properties.

Vastus medialis and lateralis activity during voluntary and stimulated contractions.

INTRODUCTION: The purpose of this study was to investigate the relative activation of vastus medialis (VM) and vastus lateralis (VL) muscles during voluntary and stimulated isometric contractions at different joint angles. METHODS: Sixteen healthy men (mean age: 26 years) completed maximal voluntary and stimulated contractions of the knee extensor muscles at 30°, 65°, and 100° of knee flexion. VM/VL ratios were calculated from voluntary electromyographic (EMG) and evoked torque recordings. RESULTS: Both EMG and VM/VL torque ratios were significantly lower at 30° than at 100° of knee flexion (P < 0.05). CONCLUSIONS: These results can be explained by the relatively small contribution of the VM muscle to knee extension torque at short muscle length. Such disadvantage of the VM muscle at extended knee positions does not seem to be compensated by an increased neural drive. Muscle Nerve 56: 968-974, 2017.

Lower working heights decrease contraction intensity of shoulder muscles in a herringbone 30° milking parlor.

Musculoskeletal disorders have been a main concern in milkers for many years. To improve posture, a formula was developed in a previous study to calculate ergonomically optimal working heights for various milking parlor types. However, the working height recommendations based on the formula for the herringbone 30° parlor were broad. To clarify the recommendations for the optimal working height, we investigated the effect of working height on upper limb and shoulder muscle contraction intensities. We evaluated 60 milking cluster attachment procedures in a herringbone 30° milking parlor in 7 men and 9 women. Specifically, we examined the effect of working height on muscle contraction intensity of 4 arm and shoulder muscles bilaterally (flexor carpi ulnaris, biceps brachii, deltoideus anterior, and upper trapezius) by using surface electromyography. The working heights (low, medium, and high), which reflect the ratio of the subject's height to the height of the udder base, were used in the milking health formula to determine and fit individual depth of pits. Data were evaluated for each muscle and arm side in the functions holding and attaching. Statistical analysis was performed using linear mixed effects models, where muscle contraction intensity served as a target variable, whereas working height coefficient, sex, subject height, and repetition were treated as fixed effects, and repetition group nested in working height nested in subject was considered a random effect. Contraction intensities decreased with decreasing working height for the deltoideus anterior and upper trapezius, but not for the flexor carpi ulnaris or the biceps brachii muscles in both holding and attaching arm functions. We found that milking at a lower working height reduced muscle contraction intensities of the shoulder muscles. Women showed higher contraction intensities than men, whereas subject height had no effect. The study demonstrated that a lower working height decreased muscular load during milking. These lower working heights should be used within the recommendations made by the milking health formula for the herringbone 30°. Working heights could be adjusted effectively for milkers of varying body height. Future studies should therefore use the milking health formula as a tool to objectively compare and improve the accuracy of the working height coefficients.

Contralateral limb deficit after ACL-reconstruction: an analysis of early and late phase of rate of force development.

The aim of this study was to assess the effect of a unilateral anterior cruciate ligament reconstruction (ACLR) on maximum voluntary contraction (MVC) and explosive strength of both the involved limb and the uninvolved limb. Nineteen male athletes completed a standard isometric testing protocol 4 months post-ACLR, while 16 healthy participants served as a control group (CG). The explosive strength of the knee extensors and flexors was assessed as RFD obtained from the slope of the force-time curves over various time intervals. Both muscle groups of the involved limb had significantly lower MVC compared to the uninvolved. The involved limb also had significantly lower RFD in the late phase of contraction (140-250 ms) for both knee extensors and flexors (P < 0.05). There was no difference in MVC between the uninvolved limb and the CG. However, RFD of the uninvolved limb was lower compared to CG for both knee extensors (0-180 ms; P < 0.01) and flexors (0-150 ms; P < 0.05). ACLR leads to lower MVC and explosive strength of the involved limb. As a consequence of potential crossover (presumably neural-mediated) effects, explosive strength deficits could be bilateral, particularly in the early phase of the contraction (<100 ms).

Rate of force development: physiological and methodological considerations.

The evaluation of rate of force development during rapid contractions has recently become quite popular for characterising explosive strength of athletes, elderly individuals and patients. The main aims of this narrative review are to describe the neuromuscular determinants of rate of force development and to discuss various methodological considerations inherent to its evaluation for research and clinical purposes. Rate of force development (1) seems to be mainly determined by the capacity to produce maximal voluntary activation in the early phase of an explosive contraction (first 50-75 ms), particularly as a result of increased motor unit discharge rate; (2) can be improved by both explosive-type and heavy-resistance strength training in different subject populations, mainly through an improvement in rapid muscle activation; (3) is quite difficult to evaluate in a valid and reliable way. Therefore, we provide evidence-based practical recommendations for rational quantification of rate of force development in both laboratory and clinical settings.