Nicola A. Maffiuletti

Physiological and methodological considerations for the use of neuromuscular electrical stimulation

The main aim of this review is to discuss some evidence-based physiological and methodological considerations for optimal use of neuromuscular electrical stimulation (NMES) in healthy and impaired skeletal muscles. After a quick overview of the main applications, interests and limits of NMES use, the first section concentrates on two crucial aspects of NMES physiology: the differences in motor unit recruitment pattern between NMES and voluntary contractions, and the involvement of the nervous system during peripheral NMES. The second section of the article focuses on the most common NMES parameters, which entail the characteristics of both the electrical current (the input) and the evoked contraction (the output).

Femoroacetabular Impingement in Professional Ice Hockey Players A Case Series of 5 Athletes After Open Surgical Decompression of the Hip

Background Femoroacetabular impingement of the hip joint has been identified as a major cause for hip pain in athletes. Surgical open decompression of the hip has historically been proposed as the first treatment of choice. Functional outcomes in athletes after this procedure are unknown. Purpose To describe the functional and sport-related outcome 2 years after open surgical hip decompression in a group of young professional ice hockey players suffering from cam femoroacetabular impingement. Study Design Case series; Level of evidence, 4. Methods Five young professional ice hockey players (mean age, 21.4 y at follow-up) who suffered from cam femoroacetabular impingement were treated with open surgical decompression of the hip. The operation was performed by the same surgeon, and all athletes followed the same rehabilitation guidelines. Mean follow-up time was 2.7 years. Outcome measures were recorded as time to regain symmetrical hip rotation, regain preoperative core/hip muscle strength, return to team practice, and play at competitive level. Results Hip rotation range of motion was regained by a mean 10.3 weeks. Core and hip strength values reached preoperative levels by a mean 7.8 months. Return to unrestricted team practice with the ice hockey team was achieved by a mean 6.7 months, and athletes were able to play their first competitive game after a mean 9.6 months. Three athletes were able to perform again at the highest level and in international competitions. Two athletes had to return to minor league ice hockey. Conclusion Return to high-level ice hockey after open surgical decompression of the hip was possible in this series of 5 consecutive cases.

Evidence of neuromuscular fatigue after prolonged cycling exercise.

PURPOSE The purpose of this study was to analyze the effects of prolonged cycling exercise on metabolic, neuromuscular, and biomechanical parameters. METHODS Eight well-trained male cyclists or triathletes performed a 2-h cycling exercise at a power output corresponding to 65% of their maximal aerobic power. Maximal concentric (CON; 60, 120, 240 degrees x s(-1)), isometric (ISO; 0 degrees s(-1)), and eccentric (ECC; -120, -60 degrees x s(-1)) contractions, electromyographic (EMG) activity of vastus lateralis (VL) and vastus medialis (VM) muscles were recorded before and after the exercise. Neural (M-wave) and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed using electrical stimulation techniques. RESULTS Oxygen uptake (VO2), minute ventilation (VE), and heart rate (HR) significantly increased (P < 0.01) during the 2-h by, respectively, 9.6%, 17.7%, and 12.7%, whereas pedaling rate significantly decreased (P < 0.01) by 21% (from 87 to 69 rpm). Reductions in muscular peak torque were quite similar during CON, ISO, and ECC contractions, ranging from 11 to 15%. M-wave duration significantly increased (P < 0.05) postexercise in both VL and VM, whereas maximal amplitude and total area decreased (VM: P < 0.05, VL: NS). Significant decreases in maximal twitch tension (P < 0.01), total area of mechanical response (P < 0.01), and maximal rate of twitch tension development (P < 0.05) were found postexercise. CONCLUSIONS A reduction in leg muscular capacity after prolonged cycling exercise resulted from both reduced neural input to the muscles and a failure of peripheral contractile mechanisms. Several hypothesis are proposed to explain a decrease in pedaling rate during the 2-h cycling with a constancy of power output and an increase in energy cost.

Validity and reliability of Optojump photoelectric cells for estimating vertical jump height.

Glatthorn, JF, Gouge, S, Nussbaumer, S, Stauffacher, S, Impellizzeri, FM, and Maffiuletti, NA. Validity and reliability of Optojump photoelectric cells for estimating vertical jump height. J Strength Cond Res 25(2): 556-560, 2011-Vertical jump is one of the most prevalent acts performed in several sport activities. It is therefore important to ensure that the measurements of vertical jump height made as a part of research or athlete support work have adequate validity and reliability. The aim of this study was to evaluate concurrent validity and reliability of the Optojump photocell system (Microgate, Bolzano, Italy) with force plate measurements for estimating vertical jump height. Twenty subjects were asked to perform maximal squat jumps and countermovement jumps, and flight time-derived jump heights obtained by the force plate were compared with those provided by Optojump, to examine its concurrent (criterion-related) validity (study 1). Twenty other subjects completed the same jump series on 2 different occasions (separated by 1 week), and jump heights of session 1 were compared with session 2, to investigate test-retest reliability of the Optojump system (study 2). Intraclass correlation coefficients (ICCs) for validity were very high (0.997-0.998), even if a systematic difference was consistently observed between force plate and Optojump (−1.06 cm; p < 0.001). Test-retest reliability of the Optojump system was excellent, with ICCs ranging from 0.982 to 0.989, low coefficients of variation (2.7%), and low random errors (±2.81 cm). The Optojump photocell system demonstrated strong concurrent validity and excellent test-retest reliability for the estimation of vertical jump height. We propose the following equation that allows force plate and Optojump results to be used interchangeably: force plate jump height (cm) = 1.02 × Optojump jump height + 0.29. In conclusion, the use of Optojump photoelectric cells is legitimate for field-based assessments of vertical jump height.

ASSESSMENT OF THE RELIABILITY OF CENTRAL AND PERIPHERAL FATIGUE AFTER SUSTAINED MAXIMAL VOLUNTARY CONTRACTION OF THE QUADRICEPS MUSCLE

The aim of the present study was to further confirm the validity of measurements for characterizing neuromuscular alterations by establishing their reliability both before and after fatigue. Thirteen men (28 ± 5 years) volunteered to participate in two separate identical sessions requiring the performance of a sustained maximal voluntary contraction (MVC) with the quadriceps muscle for 2 min. MVC and transcutaneous electrical stimulations were used before and immediately after the fatiguing contraction to investigate the reliability of MVC torque, central activation, and peripheral variables (M‐wave properties, peak twitch, peak doublet) within and between sessions. Based on previous and present results, we advise the use of (1) voluntary activation level with potentiated doublet as a reference to describe central fatigue, (2) electromyographic activity of vastus lateralis muscle as a surrogate for quadriceps for both voluntary and evoked contraction, and (3) potentiated peak doublet amplitude to investigate contractile fatigue. These findings can be useful in the choice of the parameters describing central and peripheral fatigue of the quadriceps muscle in future studies. Muscle Nerve, 2007

Reliability of isokinetic strength imbalance ratios measured using the Cybex NORM dynamometer

The main aim of this study was to examine the absolute and relative reliability of some commonly used strength imbalance indices such as concentric hamstring‐to‐concentric quadriceps ratio, eccentric hamstring‐to‐concentric quadriceps ratio and bilateral concentric and eccentric strength ratios. An additional aim was to examine the reliability of the peak torque and work of the knee extensor and flexor muscles measured using the Cybex NORM dynamometer. Eighteen physically active healthy subjects (mean ± standard deviation, age 23 ± 3 years, height 176 ± 5 cm, body mass 74 ± 8 kg) were tested three times with 96 h between sessions. Peak torque, average work, unilateral and bilateral ratios were determined at 60, 120, 180 and −60° s−1. Low (0·34) to moderate (0·87) relative reliability (intraclass correlation coefficient, ICC) was found for strength imbalance ratios with eccentric hamstring‐to‐concentric quadriceps ratio showing the greater ICC (>0·80). High ICC values (0·90–0·98) were found for peak torque and average work. Absolute reliability (standard error of measurement) ranged from 3·2% to 8·7% for strength imbalance ratios and from 4·3% to 7·7% for peak torque and average work measurements. This study established the reliability of the most common strength imbalance ratios and of absolute isokinetic muscle strength assessed using the Cybex NORM.

Reliability of knee extension and flexion measurements using the Con‐Trex isokinetic dynamometer

The aim of this study was to evaluate the reliability of isokinetic and isometric assessments of the knee extensor and the flexor muscle function using the Con‐Trex isokinetic dynamometer. Thirty healthy subjects (15 males, 15 females) were tested and retested 7 days later for maximal strength (isokinetic peak torque, work, power and angle of peak torque as well as isometric maximal voluntary contraction torque and rate of torque development) and fatigue (per cent loss and linear slope of torque and work across a series of 20 contractions). For both the knee extensor and the flexor muscle groups, all strength data – except angle of peak torque – demonstrated moderate‐to‐high reliability, with intraclass correlation coefficients (ICC) higher than 0·86. The highest reliability was observed for concentric peak torque of the knee extensor muscles (ICC = 0·99). Test–retest reliability of fatigue variables was moderate for the knee extensor (ICC range 0·84–0·89) and insufficient‐to‐moderate for the knee flexor muscles (ICC range 0·78–0·81). The more reliable index of muscle fatigue was the linear slope of the decline in work output. These findings establish the reliability of isokinetic and isometric measurements using the Con‐Trex machine.

Sports After Hip Resurfacing Arthroplasty

Background No information is available concerning patients’ sports activity after hip resurfacing arthroplasty. Hypothesis Patients treated by hip resurfacing arthroplasty will be able to achieve a high level of sports activity. Study Design Case series; Level of evidence, 4. Methods We surveyed 112 patients by postal questionnaire to determine their sporting activities at a mean of 23.5 (range, 9—40) months after hip resurfacing surgery. Data were also analyzed separately for older and younger patients and women and men, respectively. Results Of 112 patients, 110 participated in an average of 4.6 sport disciplines after surgery, compared with 105 patients preoperatively engaged in an average of 4.8 disciplines. About 26% performed sports 4 times per week or more—almost 60% for longer than 60 min at each session. A high proportion of our patients were still engaged in downhill skiing (51%) and in high-impact disciplines such as tennis (12%) or contact sports (22%). More than 50% of the patients commenced sports within the first 3 months after surgery. During activities, 70% were completely pain-free. The group of older patients (mean age, 60.2 years) participated in more different disciplines with a higher weekly frequency and longer session length than younger patients (mean age, 46.4 years). Conclusion The present study reports for the first time on the detailed sports activity and activity extent after hip resurfacing arthroplasty. Our patients could return to a high level of sports participation after surgery. Age-related differences were found that have not yet been published. Nevertheless, further follow-up is necessary to assess the influence of high-level activity on loosening and revision rates after hip resurfacing arthroplasty.

Hip muscle weakness in patients with symptomatic femoroacetabular impingement

OBJECTIVE Femoroacetabular impingement (FAI) is a pathomechanical process, which may cause hip pain, disability and early development of hip osteoarthritis (OA) in young and active adults. Patients with FAI experience functional disability during dynamic weight-bearing activities, which could originate from weakness of the hip muscles. The objective of this study was to compare hip muscle strength between patients with symptomatic FAI and healthy controls. It was hypothesized that patients would present overall hip muscle weakness compared to controls. METHODS A total of 22 FAI patients and 22 controls matched for gender, age, and body mass participated in the study. We evaluated isometric maximal voluntary contraction (MVC) strength of all hip muscle groups using hand-held and isokinetic dynamometry, and electromyographic (EMG) activity of the rectus femoris (RF) and tensor fasciae latae (TFL) muscles during active flexion of the hip. RESULTS FAI patients had significantly lower MVC strength than controls for hip adduction (28%), flexion (26%), external rotation (18%) and abduction (11%). TFL EMG activity was significantly lower in FAI patients compared with controls (P=0.048), while RF EMG activity did not differ significantly between the two groups (P=0.056). CONCLUSIONS Patients with symptomatic FAI presented muscle weakness for all hip muscle groups, except for internal rotators and extensors. Based on EMG recordings, it was demonstrated that patients with symptomatic FAI have a reduced ability to activate TFL muscle during hip flexion. These findings provide orthopedic surgeons with objective information about the amount and specificity of hip muscle weakness in patients with FAI. Future research should investigate the relationship between hip muscle weakness, functional disability and overuse injury risks, as well as the effects of hip muscle strengthening on clinical outcomes in individuals with symptomatic FAI.

Effect of cycling cadence on contractile and neural properties of knee extensors

PURPOSE This study investigated the effect of prior prolonged cycling exercise performed at different cadences on subsequent neuromuscular characteristics. METHODS Eight well-trained triathletes sustained 80% of their maximal aerobic power during 30 min at three cadences: the freely chosen cadence (FCC), FCC-20%, and FCC+20%. Maximal isometric and concentric (120 degrees x s(-1) and 240 degrees x s(-1)) torques were recorded before and after the exercise. Central activation, neural (M-wave), and contractile (isometric muscular twitch) parameters of quadriceps muscle were also analyzed by electrical stimulation of the femoral nerve. RESULTS Reductions in maximal isometric (P < 0.01) and concentric torques at 120 degrees x s(-1) (P < 0.05) were found after exercise. Central activation levels fell significantly (P < 0.05) by 13-16% depending on the pedaling rate. Although the M-wave did not significantly change after exercise, the ratio EMG RMS/M-wave amplitude decreased significantly (P < 0.01) on both vastus lateralis and vastus medialis muscles for FCC-20% and FCC but not for FCC+20%. Significant decreases in maximal twitch tension (P < 0.01), maximal rate of twitch development (P < 0.01), and time to half relaxation (P < 0.01) were observed postexercise with no effect of cadence. CONCLUSIONS These findings suggest that force reduction after prolonged cycling is attributable to both central and peripheral factors but is not influenced by the pedaling rate in a range of FCC +/- 20%.