The aim of this study was to determine the baseline neuromuscular tensiomyography (TMG) parameters of knee extensor and flexor muscles in amateur road cyclists and then calculated percentages for the lateral symmetry and the functional symmetry. Twelve Spanish amateur road cyclists, category Elite, were considered (age 18.7 ± 0.7 years, body mass 68.0±8.2 kg, height 180.1±5.4 cm; fat 8.8±2.3%; maximal power output5.6±0.3 w/kg).The cyclists were assessed, through TMG, on the first days of the pre-season, after a rest period of 3 weeks, at least 48 hours after performing any physical activity. A paired-samples t test (p<.05) was used to compare sides (dominant vs. non-dominant lower limb) and one-way ANOVA with the Bonferroni test (p < .01) was applied, with muscle being taken as an independent factor. No significant differences were observed between the dominant and non-dominant leg except in maximum radial displacement and contraction velocity of rectus femoris. Lateral symmetry percentages obtained were of about 82% in all muscles and functional symmetry percentages obtained were above 73%. This is due to higher contraction time (between 11.8 and 16.9 ms, p < .01) and lower contraction velocity (between 65.5 y 123.9 mm·s-1p < .01) of cyclist´s biceps femoris about knee extensor muscles. The neuromuscular evaluation of the principal muscles of pedalling at the beginning of the training season may set initial values of reference in theoretical absence of fatigue. So that it becomes a tool that helps the coach to control and study subsequently the changes that occur due to the training loads and competition that receives the cyclist during the different training cycle of the season. Moreover, in case of muscle tendon injury would help to identify the anomalous values product of the injury and carry out the monitoring of the recovery.

Season , Cycling , Muscle contraction , Symmetry , Asymmetry

García-García O (2015) Preseason Neuromuscular Profile of Knee Extensor and Flexor Muscles in Elite Amateur Road Cyclist’s Assessment through Tensiomyography. Ann Sports Med Res 2(3): 1024.

TMG: Tensiomyography; Ms: Milliseconds; Mm: Millimeters; W: Watios; Ma: Milliamperes; Cm: Centimeters; LS: Lateral Symmetry; FS: Functional Symmetry

To evaluate the relation or balance between different muscles acting on a given joint or on different side of the body, it may be used different techniques and tools. Some such as carrying out a comparative test of maximum strength, or the comparison of the power developed by each muscle group measured with a rotary encoder [1].

Also, the muscle function of cyclists can be assessed by means of tensiomyography (TMG), a non-invasive technique that, by means of a portable device, can measure the properties of individual superficial muscles by recording the isometric muscle contraction induced externally by electrostimulation. TMG can provide information about the muscle fibre type composition [2,3], muscle tone [4], muscle fatigue [5], and muscle imbalance and asymmetries [6,7]. The possibility of assessing isolated muscles in the field, avoiding the influence of factors such as motivation, gives TMG an advantage over the other methods as maximum strength, the force produced at different angles and speeds, and muscle power.

The aim of this study was to determine the baseline neuromuscular TMG parameters of knee extensor and flexor muscles in amateur road cyclists and then calculated percentages for the lateral symmetry and the functional symmetry.

Participants

Twelve Spanish amateur road cyclists, category Elite, were considered(age 18.7±0.7 years, body mass 68.0 ±8.2 kg, height 180.1±5.4 cm; fat 8.8±2.3%; maximal power output obtained in a progressive maximal test in a laboratory5.6±0.3 W/kg). They were in good health and injury-free and they had passed the medical examination. All participants provided written consent subsequent to being informed about the research process and the possible risks of TMG assessment. The coaching staff and management board were also informed about the nature of the study. The research protocol followed the principles of the Declaration of Helsinki regarding biomedical research involving human subjects. The local ethics committee approved the study.

Procedure

The cyclists were assessed on the first days of the pre-season, after a rest period of 3 weeks, at least 48 hours after performing any physical activity. TMG was used to measure the radial muscle belly displacement of the vastus medialis (VM), vastus lateralis (VL) and rectus femoris (RF) knee extensor muscles, and of the long head of the biceps femoris (BF) flexor muscle. Knee extensors were measured with the knee joint fixed at an angle of 120º and the knee flexor muscle was measured with the knee joint fixed at an angle of 150º.

The TMG assessments were performed once the subject had been in a relaxed supine position for 10-15 minutes following the protocol described by García-García et al. [8] with professional cyclists. Electrical stimulation was applied with pulse duration of 1 ms and initial current amplitude of 30 mA, which was progressively increased in 5 mA steps until reaching 110 mA (maximal stimulator output). Only the curve with the highest maximum radial displacement was included in the analysis for each muscle assessed. In order to obtain repeatability coefficients for the TMG parameters, two measurements were taken at random from one of the cyclist’s muscles; the sensor and electrode position used for the first measurement was marked so that they could be placed in the same location when taking the second measurement 20-30 minutes later.

Measures of radial muscle belly displacement were acquired by means of a digital displacement transducer (GK 30, Panoptikd.o.o., Ljubljana, Slovenia) set perpendicular to the thickest part of the muscle belly. The thickest part of the muscle belly was determined visually and through palpation during a voluntary contraction. The self-adhesive electrodes (5x5 cm, Cefar-Compex Medical AB Co., Ltd, Malmö, Sweden) were placed symmetrically at a distance of 5 cm from the sensor. A TMG-S2 stimulator (EMF-FURLAN & Co. d.o.o., Ljubljana, Slovenia) produced the electrical stimulus.

Each measurement involved recording the following parameters of involuntary isometric contraction produced by the electrical stimulus. Maximum radial muscle belly displacement (Dm) in mm. Contraction time (Tc ) as the time in ms from 10% to 90% of Dm. Delay time (Td ) as the time in ms from onset to 10% of Dm. Sustain time (Ts) as the time in ms between 50% of Dm on both the ascending and descending sides of the curve. Halfrelaxation time (Tr ) as the time in ms between 90% and 50% of Dm on the descending curve. Contraction velocity (Vc ) as the rate (mm·s-1) between the radial displacement occurring during the time period of Tc (Dm80) and Tc [Dm80/Tc ].

Statistical analysis

Application of the Kolmogorov-Smirnov test, in conjunction with the Lilliefors test (p < .05), showed that the sample distribution was normal, linear and homoscedastic. Intraclass correlation coefficients (ICCs) with a 95% confidence interval (CI) were used to assess the reliability of TMG measurements. A paired-samples t test (p<.05) was used to compare sides (dominant vs. non-dominant lower limb). One-way ANOVA with the Bonferroni test (p < .01) was applied, with muscle being taken as an independent factor. All data were analysed using SPSS v19.0 for Windows (SPSS Inc., Chicago, IL, USA). The lateral symmetry (LS) and functional symmetry (FS) percentages were calculated using the algorithm implemented by the TMG-BMC tensiomyography® software (Figures 1,2).

The ICC values (95% CI) obtained ranged between 0.79 and 0.98: Dm, 0.98; Tc , 0.98 Ts , 0.90; Td , 0.89; and Tr , 0.79. If one considers a value below 0.8 as the cut-off for insufficient reliability [9], then the ICCs for these pre-season data indicate good reliability for all the TMG parameters except Tr parameter. TMG measurements of these muscles have previously been reported to show good same-day reliability [10-12], except Tr parameter [11] coinciding with our findings. In addition, research has suggested that TMG measurements are also reliable when tests are performed on

Figure 1: LS= lateral symmetry, where “r” is the right side and “l” is the left side in all parameters. Min= minimum; Max=maximum.

Figure 2: FS= Functional symmetry, where “r” is the right side and “l” is the left side in all parameters. Min= minimum; Max=maximum.

consecutive days [13], it is important to establish the baseline of neuromuscular profile.

The maximal power output (Wmax) is a performance indicator whose ratio power/weight must be higher than 5.5 W/ kg for an athlete to be considered as a top-level cyclist [14].The Wmax of the cyclists of this sample (5.6±0.3 W/kg)is in line with this value. It is higher than the values reported in senior amateur cyclists (4.6±0.3 W/kg) [15]. In addition, the body fat percentage of this sample (8.8±2.3%) is lower than the values reported in senior amateur cyclists (17.3±5%) [15], although using different method.

No significant differences were observed between the dominant and non-dominant leg (table 1) except in Dm of RF (10±1.6 vs 7.5±1.2, p<0.001) and Vc of RF (256.1±36.6 vs 203.9±53.7 mm·s-1 p= 0.005). Lateral symmetry percentages (LS) obtained through the algorithm implemented by the TMG-BMC tensiomyography® software were 82.4±13.8% for BF, 85.2±3.9% for RF, 89.5±4.9% for VL, and 91.8±4.6% for VM (Table 1).

These finds are consistent with the lack of significant differences between both legs of professional volleyball players [16] of professional cyclists [6], and of professional soccer players [17,18] also tested with TMG. In fact, although the latter authors did report some differences in certain parameters of the VM (Tc ), VL (Tc and Td ), RF (Ts and Tr ) and BF (Ts) they concluded that TMG measurements of soccer players are not generally influenced by leg dominance [18]. So it has been suggested that having into account that there are no meaningful differences in both sides, when the percentage of LS determined by software TMG is above to 80%, it could be considered as appropriate [6]. LS percentages of this sample are in accordance with the informed about professional cyclists indicating a LS average percentage of 82.2±9.8%of these four assessed muscles [6]

Functional symmetry percentages (FS) obtained through the algorithm implemented by the TMG-BMC tensiomyography® software were 75.2±19. 3% for dominant lower limb and 73.0±18.2% for non-dominant lower limb. These values are in accordance with those found in professional cyclists throughout the season with a 77.4±9% in the preparatory period and 73.2±8.8% in the competitive period [6]. Normal values of functional symmetry in high-level beach volleyball players are around 65% or more [19]. The cyclists are above of this reference value, this finding is expected in a cyclical sport.

Namely it may be seen in Table 2 that the Tc of the BF is significantly higher (between 11.8 and 16.9 ms) than the Tc of the three knee extensors, RF, VL and VM, that the Ts of the BF is also significantly higher than RF and VL (in 90.7 and 73.4 ms respectively). Finally the Vc of the BF is significantly lower than the Vc of the knee extensors (between 65.5 y 123.9 mm·s-1) (Table 2).

The Tc is related to the predominance of the type of muscle fiber [2] and it has also been significantly related to the percentage of MHC-I in the Vastus Lateralis [3], also TC can be attributed to the higher percentage of slow-twitch fibers - type 1 in Vastus Medialis [20]. Indeed, the amplitude of the TMG response is directly related to contractile force up to about 68% of the maximum [4], that is, under performance zones of fasttwitch fibers- type II (in isometric contraction or slow velocity performance in concentric contraction),so the higher the Tc are, more predominance of slow fibers will have the athlete. That is, the BF of these cyclists is slower when they contract than the knee extensors, which can be seen graphically in Figure 3.

In addition, it has been reported that to be able to compare the scores obtained from different muscles, it is necessary to normalize this time rise [21]. The Vc represents this normalization and the lower Vc of the BF, respect the knee extensors, is in line with the stated above.

The Tc of the BF of the professional cyclists are also significantly higher than the knee extensors during the preparatory period [6].However, the result of the amateur cyclists of this sample is higher (42.1±14.5 vs 38.9±12.9ms in dominant lower limb; 43.0±16.6 vs 32.8±9.3ms in non-dominant lower limb) to that found in the professional cyclists [8].Although to be evaluated in their preparatory period, with a volume of training around 1,150±279 kilometers (range of 700-1,600 km), and not at the beginning of this, may partly explain this different found, since their evolution during the season marks a significant downward trend, in contrast, the knee extensors significantly increase their values [8]. In fact, the Tc of the knee extensors is lower than 

Table 1: Differences between dominant vs. non-dominant lower limb in TMG assessments of cyclists. Tc , Td, Ts and Tr are in ms, while Dm is in mm, and Vc is in mm·s-1.Difference between lower limbs is significant at p < .05*.Values are mean and standard deviation.

Abbreviations: Dm: Maximum Radial Muscle Belly Displacement; Tc : Contraction Time; Td : Delay Time; Ts : Sustain Time; Tr : Half-Relaxation Time; Vc : Contraction Velocity

Figure 3: T differences between muscles indominant and non-dominant lower limbs. T are in ms. Difference between T is significant at p < .01*.

Table 2: Differences between cyclists’ muscles assessments. Mean difference and standard deviation. Tc , Td , Ts and Tr are in ms, while Dm is in mm, and Vc is in mm·s-1. One-way ANOVA with the Bonferroni test (p<.01) muscle as an independent factor.

Abbreviations: Dm: Maximum Radial Muscle Belly Displacement; Tc : Contraction Time; Td : Delay Time; Ts : Sustain Time; Tr : Half-Relaxation Time; Vc : Contraction Velocity. BF: Biceps Femoris; RF: Rectus Femoris; VL: Vastus Lateralis; VM: Vastus Medialis.

professional cyclists [8] in their preparatory period (RF 35.9 ms; 28.3ms VL, VM 28.7ms).

Furthermore, it has also been noted that excessive muscle mass of the hamstring muscle produces some imbalance, leading to asymmetry between the knee extensor and flexor muscles, causing pain in the knee joint [19].On the other hand, it has been suggested in professional cyclists a positive correlation between VO2max and DM of the BF (r = 0.68; p<0.05), and between Wmax and DM of the BF (r = 0.65; p<0.05) [22].According to the obtained results the BF also appear to be a key muscle in the monitoring and control of the state of neuromuscular form of the cyclist, which is not a surprise, because the biceps femoris (biarticularity muscle) are activated along with the knee extensors in order to facilitate pedalling between 45º and 180º [23]. This activation of the flexors propitiates the conditions for the necessary elevation when the pedal gets close to 180º. The knee extensors differ only in their Ts, being the VM, which has a longer duration of the muscle contraction in relation to RF and VL (in 109 and 91.7 ms respectively).

No significant differences were observed between the dominant and non-dominant leg except in Dm and Vc of RF. Lateral symmetry percentages obtained are above 82% in all muscles and functional symmetry percentages obtained are above 73% due to higher Tc and lower Vc of cyclist´s BF about knee extensor muscles.

The neuromuscular evaluation of the principal muscles of pedaling at the beginning of the training season may set initial values of reference in theoretical absence of fatigue. So that it becomes a tool that helps the coach to control and study subsequently the changes that occur due to the training loads and competition that receives the cyclist during the different training cycle of the season. Moreover, in case of muscle tendon injury would help to identify the anomalous values product of the injury and carry out the monitoring of the recovery.

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