Nicola Petrone

The Effect of Stance Width on the Electromyographical Activity of Eight Superficial Thigh Muscles During Back Squat With Different Bar Loads

Paoli, A, Marcolin, G, and Petrone, N. The effect of stance width on the electromyographical activity of eight superficial thigh muscles during back squat with different bar loads. J Strength Cond Res 23(1): 246-250, 2009-Many strength trainers believe that varying the stance width during the back squat can target specific muscles of the thigh. The aim of the present work was to test this theory measuring the activation of 8 thigh muscles while performing back squats at 3 stance widths and with 3 different bar loads. Six experienced lifters performed 3 sets of 10 repetitions of squats, each one with a different stance width, using 3 resistances: no load, 30% of 1-repetition maximum (1RM), and 70% 1RM. Sets were separated by 6 minutes of rest. Electromyographic (EMG) surface electrodes were placed on the vastus medialis, vastus lateralis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus, gluteus medium, and adductor maior. Analysis of variance and Scheffè post hoc tests indicated a significant difference in EMG activity only for the gluteus maximus; in particular, there was a higher electrical activity of this muscle when back squats were performed at the maximum stance widths at 0 and 70% 1RM. There were no significant differences concerning the EMG activity of the other analyzed muscles. These findings suggest that a large width is necessary for a greater activation of the gluteus maximus during back squats.

Multiaxial fatigue life estimations for 6082-T6 cylindrical specimens under in-phase and out-of-phase biaxial loadings

Fully reversed bending/torsion fatigue tests were conducted on 6082-T6 solid cylindrical specimens under force control. Specimens were subjected to pure bending, pure torsion, in-phase and out-of-phase bending/torsion loadings and the investigated fatigue lives ranged between 104 and 2.106 cycles to failure. The actual strains were measured by means of strain gauges positioned in correspondence of critical points. Experimental strain measurements highlighted that all the tests were conduced in pure elastic stress conditions. The material fatigue behaviour was studied by analysing the cracks pattern due to the considered biaxial loadings. All the tests showed that crack initiation was always MODE II dominated (that is, it occurred on the plain of maximum shear stress amplitude), whereas the crack propagation was MODE I governed. Just in the presence of pure torsional loadings cracks grew under MODE II loadings. A good correlation with measured fatigue lives was obtained by applying the Susmel and Lazzarins criterion valid for homogeneous and isotropic materials, despite the slight degree of anisotropy showed by the material.

Reducing the risks for traumatic and overuse injury among competitive alpine skiers

To achieve success, skiers attempt to optimise various biomechanical parameters (eg, trajectory, velocity, interaction between the skis and snow, energy) that influence performance,1 but this increases risk of injury.2 It is therefore not surprising that injuries are common among alpine skiers.3 To reduce the injury rate, the International Ski Federation (FIS) regulates ski length and width, sidecut radius, and the distance between the foot and ground. In the case of slalom skis, only the minimal waist width is regulated (≥63 mm), while in other disciplines the maximal waist width is regulated by FIS (typically ≤65 mm). On hard snow, wider skis are associated with an elevated risk for injury,4 so we suggest that it may be wise to revise this FIS regulation. Measures concerning the geometry of skis implemented recently have contributed significantly to the 26% reduction in absolute injury rate (injuries/100 athletes/season) (risk ratio 0.74, 95% CI 0.63 to 0.87).3 We acknowledge that new regulations concerning helmets, the development …

Biomechanical Analysis of Olympic Kayak Athletes During Indoor Paddling

The aim of the work was the biomechanical analysis of elite female Olympic kayak athletes during indoor paddling on ergometers. An integrated motion capture system was used for the acquisition of paddle trajectory, trunk and limbs motion and for the measure of forces developed by the athletes on a dynamometric footpad. Several quantitative biomechanical parameters were correspondently defined. Symmetry and regularity criteria were adopted to define a skill classification for each analysis parameter and a final correlation with sport results classification was investigated. This will help trainers to define suitable functional evaluation methods.

Selective Activation of Shoulder, Trunk, and Arm Muscles: A Comparative Analysis of Different Push-Up Variants.

CONTEXT The push-up is a widely used exercise for upper limb strengthening that can be performed with many variants. A comprehensive analysis of muscle activation during the ascendant phase (AP) and descendant phase (DP) in different variants could be useful for trainers and rehabilitators. OBJECTIVE To obtain information on the effect of different push-up variants on the electromyography (EMG) of a large sample of upper limb muscles and to investigate the role of the trunk and abdomen muscles during the AP and DP. DESIGN Cross-sectional study. SETTING University laboratory. PATIENTS OR OTHER PARTICIPANTS Eight healthy, young volunteers without a history of upper extremity or spine injury. INTERVENTION(S) Participants performed a set of 10 repetitions for each push-up variant: standard, wide, narrow, forward (FP), and backward (BP). Surface EMG of 12 selected muscles and kinematics data were synchronously recorded to describe the AP and DP. MAIN OUTCOME MEASURE(S) Mean EMG activity of the following muscles was analyzed: serratus anterior, deltoideus anterior, erector spinae, latissimus dorsi, rectus abdominis, triceps brachii caput longus, triceps brachii caput lateralis, obliquus externus abdominis, pectoralis major sternal head, pectoralis major clavicular head, trapezius transversalis, and biceps brachii. RESULTS The triceps brachii and pectoralis major exhibited greater activation during the narrow-base variant. The highest activation of abdomen and back muscles was recorded for the FP and BP variants. The DP demonstrated the least electrical activity across all muscles, with less marked differences for the abdominal and erector spinae muscles because of their role as stabilizers. CONCLUSIONS Based on these findings, we suggest the narrow-base variant to emphasize triceps and pectoralis activity and the BP variant for total upper body strength conditioning. The FP and BP variants should be implemented carefully in participants with low back pain because of the greater activation of abdominal and back muscles.

Static and Dynamic Postural Changes after a Mountain Ultra-Marathon of 80 km and 5500 D+

The study aimed to investigate the effect of fatigue on static and dynamic postural stability after completing a mountain ultra-marathon. Twelve male athletes participated in the study. Postural stability was assessed before and immediately after the race. Static postural stability was evaluated on a dynamometric platform with eyes opened (OE) and closed (CE). Dynamic postural stability was assessed with OE on an instrumented plate which allowed medio-lateral oscillations. Stabilometric data were affected by fatigue in the OE condition, concerning sway path velocity (p = 0.0006), sway area velocity (p = 0.0006), area of the confidence ellipse (p = 0.0016), maximal anterior-posterior (AP) (p = 0.0017) and medio-lateral (ML) (p = 0.0039) oscillations. In the CE condition the sway path velocity (p = 0.0334), the maximal ML oscillations (p = 0.0161) and the area of the confident ellipse (p = 0.0180) were also negatively influenced. Stabilogram diffusion analysis showed in the OE condition an increase of short-term diffusion coefficients considering the anterior-posterior direction (Dfys; p = 0.0023) and the combination of the two (Dfr2s; p = 0.0032). Equally, long term diffusion coefficients increased considering the anterior-posterior direction (Dfyl; p = 0.0093) and the combination of the two (Dfr2l; p = 0.0086). In CE condition greater values were detected for medio-lateral direction (Dfxl; p = 0.033), anterior-posterior direction (Dfyl; p = 0.0459) and the combination of the two (Dfr2l; p = 0.0048). The dynamic postural stability test showed an increase of the time spent with the edges of the plate on the floor (p = 0.0152). Our results showed that mountain ultra-marathon altered static stability more than dynamic stability. An involvement of cognitive resources to monitor postural stability after fatiguing could be the explanation of the worsening in the automatic task (quiet standing) and of the positive compensation in the less automatic task (dynamic standing on the instrumented plate).

The effect of impact speed, construction, and layout of different ski safety barriers on peak decelerations and penetration values of a solid dummy during full scale impacts

Collisions with fixed obstacles during alpine ski competitions or recreational skiing seldom occur, but if they do the consequences can be severe, particularly in the case of competitions in which safety barriers are mandatory. Despite its importance, a standard method for evaluating the crashworthiness of such equipment has not yet been established. The aim of this work was to develop a full scale impact test method suitable for safety barriers commonly installed during Ski World Cup events. The construction and layout of different ski safety barriers, the type of rear support, and the impact speed varied throughout the tests. Peak decelerations and penetration values were measured during the impact of a dummy against a barrier. Tests were performed on B-nets with different poles and on air mattresses and foam mattresses placed on ground soil with properties similar to average snow. The mattresses were supported either by poles or by a rigid concrete wall. Tests on foam mattresses placed against the wall were conducted at increasing speeds in order to evaluate the relationship between peak deceleration and impact speed. A tower pendulum 30 m in length was used to accelerate a wooden dummy with a mass of 85 kg up to a maximum speed of about 65 km/h. The dummy was instrumented at the center of mass with a tri-axial accelerometer, equipped with a data acquisition system, and released just before impact. Impacts were fllmed using a high speed video camera. Fiberglass poles were the most effective in containing the dummy. Tests on foam mattresses against the concrete wall revealed a linear relationship between peak deceleration and speed. The method allowed analysis of the behavior of mattresses and B-nets, giving quantitative indications to manufacturers and to ski safety operators for the appropriate selection of safety barriers during competitions and in ski resorts. KEYWORDS: ski, safety barriers, mattress, net, impact, deceleration Language: en

Influence of Different Ranges of Motion on Selective Recruitment of Shoulder Muscles in the Sitting Military Press: An Electromyographic Study

Paoli, A, Marcolin, G, and Petrone, N. Influence of different ranges of motion on selective recruitment of shoulder muscles in the sitting military press: an electromyographic study. J Strength Cond Res 24(6): 1578-1583, 2010-Popular fitness literature suggests that varying the elbow range of motion (ROM) during the Military press can lead up to specific muscle isolation especially for deltoid and trapezius muscles. The purpose of the study was to examine the effect of ROM at different loads on the electromyographic (EMG) activity of 8 preselected muscles. Six experienced lifters performed 3 sets of 10 repetitions, each one with a different ROM: the first one with a final elbow angle of 90° (R1); the second with 135° (R2), and the last one with a final elbow angle of 180° (R3). Three resistances were chosen (no load, 30% of one repetition maximum [1-RM], and 70% of 1-RM), and sets were separated by 5 minutes rest. Electromyographic surface electrodes were placed on the clavicular head of pectoralis major, anterior deltoid, medial deltoid (MD), posterior deltoid (PD), upper trapezius, middle trapezius (MT), long head of triceps, and teres minor (TM). Analysis of variance showed a significant increase of rmsEMG activation with the widest ROM for each muscle and for each load condition except in MT and TM and PD with no load. The results showed that the use of the widest ROM increased the EMG activity of all the muscles selected with respect to the closest one, whereas this effect is not totally confirmed with the employment of R2. In addition, the use of intermediate ROMs was able to isolate the activity of the MD with respect to the trapezius only in the condition of the heaviest load. This suggests to coaches that in strength development programs the employment of an incomplete ROM can reduce the involvement of the trapezius without decreasing medium deltoid activation only with heavy loads.

Impact performance of standard tabletop and constant equivalent fall height snow park jumps

The theory of snow park jump design that controls landing impact has been developed, but ski resorts have not exploited this advancement, in part, because of questions of practicality. In a first step to provide a proof-of-principle example, we designed and built a novel constant equivalent fall height (EFH) snow park jump at the Tognola Ski Resort in San Martino di Castrozza, Italy. The impact performance of this jump and that of an existing standard tabletop jump were measured using a jumper on a snowboard instrumented with accelerometers. Using only the accelerometer channel perpendicular to the snowboard plane, we were able to estimate the velocity changes at impact perpendicular to the landing surface, the corresponding EFH, and approximate values of the energy absorbed on impact. These were found to be in rough agreement with the theoretical expectations for EFH derived from the measured jump profiles, including trends for the tabletop jump EFH as a function of distance jumped that have been described in the literature. Language: en

Biomechanical comparison of shorts with different pads: An Insight into the Perineum Protection Issue

Abstract An intensive use of the bicycle may increase the risk of erectile dysfunction and the compression of the perineal area has been showed to be a major mechanism leading to sexual alterations compromising the quality of life. Manufacturers claim that pads contribute to increase cyclists perineal protection ensuring a high level of comfort. To investigate the influence of various cycling pads with regard to perineal protection and level of comfort. Nine club road cyclists rode 20 min on a drum simulator, located at the Nutrition and Exercise Physiology Laboratory, at a constant speed and gear ratio wearing the shorts with 3 cycling pads of different design and thickness: basic (BAS), intermediate (INT), and endurance (END). Kinematics and pressure data were recorded at min 5, 15, and 20 of the test using a motion capture system and a pressure sensor mat. The variables of interest were: 3-dimensional pelvis excursions, peak pressure, mean pressure, and vertical force. The comfort level was assessed with a ranking order based on the subjects’ perception after the 20-min trials and measuring the vertical ground reaction force under the anterior wheel as well as the length of the center of pressure (COP) trajectory on the saddle. Results showed that the vertical force and the average value of mean pressure on the saddle significantly decreased during the 20-min period of testing for BAS and END. Mean peak pressure on the corresponding perineal cyclist area significantly increased only for BAS during the 20-min period. Interestingly objective comfort indexes measured did not match cyclists subjective comfort evaluation. The lower capacity of BAS to reduce the peak pressure on the corresponding perineal area after 20 min of testing, together with its positive comfort evaluation, suggest that a balance between protection and perceived comfort should be taken into account in the choice of the pad. Hence, the quantitative approach of objective comfort indexes introduced in this study could be helpful for manufacturers in the development of their protective pads.