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Original Research

Neuromuscular Profile of Top-Level Women Kayakers Assessed Through Tensiomyography

García-García, Oscar1; Cancela-Carral, Jose M.1; Huelin-Trillo, Fernando2

Author Information
Journal of Strength and Conditioning Research: March 2015 - Volume 29 - Issue 3 - p 844-853
doi: 10.1519/JSC.0000000000000702
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Abstract

Introduction

The neuromuscular factor seems to be a relevant predictor of performance in certain phases of the kayaking competition. On one hand, the positive relation between the level of maximum strength in specific exercises and the performance in the short sprint in elite kayakers has been demonstrated (42) and on the other hand, these neuromuscular indicators (levels of maximum strength and power) can evolve, increasing together with the cardiovasculars in the same period of training in elite kayakers (18).

These aspects are usually quantified based on parameters such as anatomical cross-sectional area, peak force, the maximum speed of shortening without load, power, or sensitivity to Ca2+ and have been used fundamentally as exercises of assessment that imply the global upper-body strength (i.e., prone bench pull, 1-arm cable row, etc), since several studies (1,12,36,44) have analyzed the kayakers' most significant morphological characteristics, as well as the kinetic chains involved in the stroke, indicating that the kinetic chain of the upper extremity (i.e., deltoideus and the trapezius muscles) and the kinetic chain of the trunk (Latissimus Dorsi) carry out the greatest effort to overcome the strength of resistance exerted by water on the boat, and these are primarily responsible for the sport success, not being conditioned by the distance of the competition (1,9).

Tensiomyography (TMG) has been incorporated to this group as a technique that allows the assessment of the superficial muscles in a noninvasive way through the registration of isometric muscular contraction induced artificially by an electrostimulator, which provides information about the muscles' contractile properties through radial deformation of the muscle belly and the time it takes to occur, to each one of the intensities used in the electric stimulus. Its advantage over other methods is that it is portable, assesses the muscles in isolation, eliminates the emotional factor of the assessment, and does not cause fatigue as a stress test, so it does not interrupt or alter the planning of the athlete. Also, it allows to assess the radial deformation of the muscle belly and the time it takes to occur, an assessment of the lateral symmetry of the muscles, which seems also relevant for kayakers, as a top-level kayaker presents an average stroke frequency of 60–90 strokes per minute, so that can carry out between 50,000 and 75,000 strokes per side weekly; although the movement of stroke is cyclic and bilateral, all kayakers present a dominant stroke side, which results in the repetitive execution of technical gesture that alters the mechanism of the kinetic chains causing asymmetry in the musculature involved in it (24).

Despite the usefulness of the TMG, reference data of these muscles (latissimus dorsi, deltoideus, and trapezius) in kayakers are not known; nevertheless, in other sports (i.e., cycling, soccer), it has been used for assessing the vastus medialis, rectus femoris, vastus lateralis, and biceps femoris muscles, used as neuromuscular reference values in top-level athletes, (13,31), or used as a mean to determine the athlete's lateral and functional symmetry, as suggested by García-García et al. (14), which can be of great significance to control the evolution of these parameters throughout the season or after being subjected to specific loads of training or competition.

The aim of this work is to assess neuromuscular characteristics and the lateral symmetry percentages of trapezius, deltoideus, and latissimus dorsi muscles in top-level women kayakers, establishing reference values in the recovery period, and to determine the influence of gender and specific training in the assessed parameters.

Methods

Experimental Approach to the Problem

To know the neuromuscular characteristics of female kayakers (FKs) and men kayakers (MKs) and muscular symmetry, it was necessary that all kayakers follow the same training schedule in their neuromuscular system, so all the assessments of TMG (FKs and MKs) took place during a recovery microcycle, after having a resting period of at least 48 hours during this microcycle. Furthermore, to determine the influence that the specific training causes in FKs, also physically active female non-kayakers (FNKs), they were assessed at least 48 hours after performing their last session of physical exercise.

FKs and MKs were assessed after their usual breakfast and before carrying out their recovery training. Before the assessment, all participants remained seated in a relaxed position for 5–8 minutes, being in a healthy state.

The measurements of 3 groups were taken by 2 experts using TMG, 1 in charge of controlling the intensity and frequency of the electrical stimulus and the other in charge of controlling the placement of the sensor and the participant status in a static and relaxed position, lying in a prone position to measure the latissimus dorsi (Figure 1), and sitting with the low back resting to measure the deltoideus (Figure 2) and the trapezius muscles (Figure 3), with the elbow bended and the hand resting on the leg.

F1-37
Figure 1:
Measure of latissimus dorsi.
F2-37
Figure 2:
Measure of deltoideus.
F3-37
Figure 3:
Measure of trapezius.

In each measurement, the following parameters of the involuntary isometric contraction caused by the electric stimulus were obtained: maximum radial displacement of the muscle (DM), measured in millimeters (mm): a high value represents a low muscle tone, tendon stiffness, or also a certain fatigue and a low value represents a high muscle tone and an increased stiffness of the tendon (16,22,30); contraction time (TC): determined between 10 and 90% of the maximum response, measured in milliseconds; reaction time (TD): determined between 0 and 10% of the maximum response, measured in milliseconds, are related to the type of fiber dominant in the assessed muscle, a high value represents a majority of type I fibers and a low value represents a majority of type II fibers (7) and also associated with fatigue, a value far above the basal point out of this circumstance (6); sustain time (TS): determined between 50% of the maximum response of the ascending curve until returning to 50% of the response, during relaxation in the descending curve, measured in milliseconds; and relaxation time (TR): determined between 90% and 50% of the maximum response in the descending curve, measured in milliseconds, report on fatigue, a high value on the basal state could indicate a potential neuromuscular fatigue (16).

To analyze the reliability of the TMG parameters, 2 measurements were taken in one of the muscles assessed from each participant at random. These measurements were taken with a difference interval between 10 and 15 minutes to each participant.

Subjects

Twenty-one volunteers participated in this study, and were stratified into 3 groups: 7 top-level women kayakers, 2 Olympics, 3 under 23s, and 2 Junior national team (FKs), who compete in distances of 200, 500, and 1,000 m (age, 22.8 ± 6.7 years; height, 166 ± 5.6 cm; body weight, 62.9 ± 5.2 kg; 49.3 ± 4.8 ml·kg−1·min−1

; 41.1 ± 4.6 ml·kg−1·min−1 anaerobic ventilatory threshold; 17.2 ± 1.1% fat; 45.4 ± 1.3% muscle mass), 4 top-level men kayakers under-23s national team (MKs) (age, 20.5 ± 2.1 years; height, 180.2 ± 7.3 cm; body weight, 78.3 ± 1.8 kg; 58.4 ± 0.7 ml·kg−1·min−1

; 45.4 ± 0.9 ml·kg−1·min−1 anaerobic ventilatory threshold, 8.5 ± 0.6% fat; 50.2 ± 0.5% muscle mass), and 10 FNKs (age, 20.1 ± 2.1 years; height, 162.7 ± 5.0 cm; body weight, 54.4 ± 6.6 kg), and have been assessed through TMG to determine the time-displacement curve of their muscles.

All participants were provided, and asked to sign, an informed consent, informing them about the research process and the possible risks of TMG assessment. In case of two junior female kayakers (FKs) under 18 their parents also signed an informed consent. In addition, coaches and members of the medical group were informed about the potential risks of the assessment and potential advantages in training using TMG.

The research protocol followed the guidelines provided by the Declaration of Helsinki on biomedical research involving human subjects (18th Medical Assembly, 1964; revised 2008 in Seoul). The research work has been approved by the local ethical committee, with the consent of the Spanish Canoe Federation.

Procedure

The procedure followed the protocol reported by Garcia-Garcia et al. (13). To assess radial displacement of the muscle belly, a digital displacement transducer was used (GK 30; Panoptik d.o.o., Ljubljana, Slovenia), which is placed perpendicularly to the thickest part of the muscle belly. The placement of the sensor was individually determined for each muscle and each kayaker because of the anatomical differences found in the athletes (43). The thickest part of the muscle belly was detected visually and through palpation during a voluntary muscular contraction.

Once the thickest part was found, it was marked with a dermatological pen. The self-adhesive electrodes (5 × 5 cm; Cefar-Compex Medical AB Co., Ltd., Malmö, Sweden) were placed following the protocol suggested by Perotto et al. (29), symmetrically separated about 5 cm from the sensor: the positive electrode was placed above the measurement point in the proximal area and the negative electrode below the measurement point in the distal area. The distance from the electrodes to the sensor was chosen because, at a distance of 5 cm, a greater muscular response can be achieved than at a distance of 3 cm, which could be caused by a greater recruitment of muscle fibers (39).

The maximum displacement of the muscle belly point was checked, in all measurements, through the calculation of the time-displacement curve characteristic of each muscle and also using low-intensity measurements (20 mA) by placing the sensor in different points, separated by 2–3 mm within the area determined by the electrodes, until achieving the exact maximum radial displacement point of the muscle belly. The electric stimulus was obtained from an electrostimulator (EMF-FURLAN & Co. d.o.o., Ljubljana, Slovenia).

The assessment of TMG was made by applying an electric stimulus of 1 millisecond of duration, whose intensity increased at intervals of 10 mA, from 30 mA until reaching 110 mA (maximal stimulator output). Between the 9 consecutive stimuli, a waiting period of 10 seconds was left to avoid fatigue signs in the muscle (22). From each kayaker, from the 9 curves registered, only the curve that obtained the greatest DM (maximum radial displacement of the muscle belly) was considered for analysis in each assessed muscle.

Statistical Analyses

The reliability of the TMG parameters was calculated through intraclass correlation coefficient reliabilities (ICCRs). The fulfillment of the assumption of normality was checked by the Kolmogorov-Smirnov test, by setting the statistical significance level at p ≤ 0.05. The distribution of the sample is normal, lineal, and homoscedastic. To determine the differences in both sides, a paired t-test was carried out (p ≤ 0.05), and we used the algorithm that TMG-BMC tensiomyography includes to determine the lateral symmetry percentages of each muscle assessed

where “r” is the right side and “l” is the left side in all parameters.

The algorithm includes 4 of the 5 parameters, both sides, of TMG (TD, TC, TS, and DM), and it does not use TR. The TC parameter and, second, the DM parameter have more importance. Finally, to determine the possible influence of group membership (FKs, MKs, FNKs) in the parameters TC, DM, TD, TS, and TR, a 1-way analysis of variance was implemented (p ≤ 0.05). In addition, Cohen's d effect sizes (ESs) for identified statistical differences were determinate. Effect sizes with values of 0.2, 0.5, and 0.8 were considered to represent small, medium, and large differences, respectively (5). The data were analyzed using the statistic package Statistical Package for the Social Sciences (SPSS, Inc., Chicago, IL, USA) for Windows (version 19.0; Statistical Package for the Social Sciences, Illinois, USA).

Results

The values of the ICCRs (confidence interval 95%) show higher reliability for the parameters DM (r = 0.96), TC (r = 0.94), and TS (r = 0.94) and good reliability for TD (r = 0.83) and TR (r = 0.80), considering a lower value of 0.8 as an insufficient reliable value (3). We could state that, in this case, the good intraday reproducibility of the TMG assessment has been confirmed.

Significant differences (p ≤ 0.05) were not found between the left and the right side of FKs, MKs, and FNKs in any of the 5 parameters gathered with TMG.

In Tables 1 and 2, it can be seen that FKs have a <19.5% (p = 0.008) TD to contract their trapezius than MKs, with a great ES (d = 2.13). The rest of the parameters measured in the 3 assessed muscles do not show significant differences and neither do their lateral symmetry percentages.

T1-37
Table 1:
Gender influence between top-level women and men kayakers in the TMG parameters of the deltoideus, trapezius, and latissimmus dorsi.*
T2-37
Table 2:
Differences between top-level women and men kayakers in the deltoideus, trapezius, and latissimus dorsi muscles.*†

The values obtained in FKs and MKs for each of the parameters assessed with TMG in each muscle are described in Table 2. These values represent the average value of both sides, as no significant differences have been found between them.

The software TMG-BMC tensiomyography provides the following lateral symmetry percentages: Deltoideus: 96.5 ± 2.1% in MKs and 90.5 ± 4.5% in FKs, which means that men are 6.0% more symmetric in this muscle; latissimus dorsi: 84.0 ± 1.4% in MKs and 84.4 ± 7% in FKs, which means that men are 0.4% less symmetric in this muscle; and trapezius: 82.5 ± 16.2% in MKs and 62.8 ± 17.1% in FKs, which means that men are 19.7% more symmetric in this muscle. These results suggest that the deltoideus is the most symmetric muscle in both genders and that the trapezius is the one with less lateral symmetry.

In Tables 3 and 4, it can be seen that FKs have a 34.4% (p = 0.003) more of TC in their latissimus dorsi and a 123.7% (p = 0.009) more in their trapezius (Figure 4), both with a great ES (d = 1.8) and (d = 1.5), respectively. Women kayakers also present an 11.3% (p = 0.01) more of TD to contract their trapezius (Figure 5), with a great ES (d = 1.5) and a higher maximum radial displacement of muscle belly (DM) of their trapezius (34.8%, p = 0.01) with a great ES too (d = 1.35) (Figure 6).

T3-37
Table 3:
Specific training influence between women non-kayakers and top-level women kayakers in the TMG parameters of the deltoideus, trapezius, and latissimmus dorsi.*
T4-37
Table 4:
Differences between women non-kayakers and top-level women kayakers in the deltoideus, trapezius, and latissimus dorsi muscles.*†
F4-37
Figure 4:
Contraction time differences between women non-kayakers and top-level women kayakers in the deltoideus, trapezius, and latissimus forsi muscles. *p ≤ 0.05.
F5-37
Figure 5:
Reaction time differences between women non-kayakers and top-level women kayakers in the deltoideus, trapezius, and latissimus dorsi muscles. *p ≤ 0.05.
F6-37
Figure 6:
Maximal radial displacement differences between women non-kayakers and top-level women kayakers in the deltoideus, trapezius, and latissimus dorsi muscles. *p ≤ 0.05.

The values obtained in FKs and FNKs for each of the parameters assessed with TMG in each muscle are described in Table 4. These values represent the average value of both sides, as no significant differences have been found between them.

The software TMG-BMC tensiomyography provides the following lateral symmetry percentages: The deltoideus (90.5 ± 4.5% in FKs and 88.5 ± 1.6% in FNKs) and latissimus dorsi (84.4 ± 7% in FKs and 87.0 ± 6.1% in FNKs) values are very similar; however, the trapezius values in FKs are 20.4% (p = 0.006) less symmetrical than those of FNKs (62.8 ± 17.1% vs. 83.2 ± 5.4%), with a great ES (d = 1.6).

Discussion

The results show that, in this sample, FKs and MKs differ only in the lower TD that the FKs obtain when contracting their trapezius (19.5%; p = 0.008; d = 2.13). However, FKs present a 34.4% more of TC (p = 0.003; d = 1.8) in their latissimus dorsi than FNKs and a 123.7% more of TC (p = 0.009; d = 1.5), an 11.3% more of TD (p = 0.01; d = 1.5), a 34.8% more of DM (p = 0.01; d = 1.35), and a 20.4% less of lateral symmetry (p = 0.006; d = 1.6) in their trapezius than FNKs.

A good ICCR was obtained in all the assessed parameters, which confirms the good intraday reliability of the use of TMG that other authors have suggested (22,31,39). The only 2 values that were lower than 0.8 were obtained in the parameter TR (31,39). In addition, TR parameter seems to show insufficient levels of long-term reliability (8), but it has been suggested that TMG measurements were reproducible across consecutive test days (34).

In view of the results, it seems that there are no substantial differences in neuromuscular characteristics between FKs and MKs; however, it seems that this top-level sport practice causes differentiating potential adaptations in the assessed muscles for the FNKs.

It seems logical not to find substantial differences between FKs and MKs, as the stretched musculature of the human body is characterized by having a physiological properties that are common and independent of gender, varying the percentage of type of fibers (oxidative, glycolytic, oxidative-glycolytic, and transitory) and its composition depending on the analyzed muscle (38). This fact suggests that the kayakers' musculature, both men and women, respond similarly to training, being the strength production directly conditioned for the cross-sectional area of the analyzed muscle and the type of fibers that is found in it (2,9,11,21,27), for the fat percentage present between the muscular fasciculus (11,27), and for the different range of movement of the joints involved in the technical gesture (41).

TD and TC parameters indicate the TD and the TC, respectively, and they depend on the kind of fiber that predominates in that muscle, the level of fatigue, and the level of activation (6), and they have also been significantly related to the percentage of Myosin heavy chain I (MHC-I) in the vastus lateralis (35), also TC can be attributed to the higher percentage of slow-twitch fibers—type 1 in vastus medialis (40). The top-level women kayakers do not differ barely of top-level men kayakers except in the TD of their trapezius (19.5%; p = 0.008; d = 2.13), suggesting that the composition of the muscles fibers between both groups of kayakers could be very similar when they receive the same training stimulus, as suggested (38) when they point out that the physiological properties of muscles are common and independent from gender.

However, FKs present a much higher TC in their latissimus dorsi (34.4%, p = 0.003; d = 1.8) and in their trapezius (123.7%; p = 0.009; d = 1.5) and also a higher TD in their trapezius (11.3%; p = 0.01; d = 1.5), than FNKs, in the deltoideus, the FK TC is also a 2.6% higher, but not significant. This fact suggests the possible specific adaptations that FKs have in these muscles, aimed at further development of type I fibers, oxidative, which allow performing 500- and 100-m test, where kayakers require a high aerobic power, besides a good lactic anaerobic capacity (4,10,26), as well as a long volume of training, which they are subjected. In brief, the aerobic contribution, expressed as a fraction of

max, was shown to be 73% for the 500 m and 85% for the 1,000 m (26). This suggestion is based on the muscular fibers that are moldable by training, causing variation in the contractile properties of fibers (23,25) and that Dahmane et al. (7) have shown indirectly that biceps femoris muscle has a strong potential to transform into faster contracting muscle after sprint training, as the average TC in sprinters was much lower (19.5 ± 2.3 milliseconds) than in the sedentary group (30.25 ± 3.5 milliseconds).

The DM parameter is related to the muscle stiffness and to the changes in the cross section of the muscle, and it can be affected by the mechanical properties of the muscular tendon, as an increase in the values of this parameter has been ascribed to a decrease of the muscle stiffness and of the tendon (30). This parameter is the one which, a priori, could have more influence over gender, as the muscle mass of the upper body seems to show the greatest differences in the level of strength between both genders, and this fact could be related to a lower percentage of muscle mass in women (27). In fact, elite women wrestlers presented lower maximum isometric and dynamic strength values than elite male wrestlers (17). However, the results of this sample do not show significant differences between MKs and FKs, which is in line with the findings of Rodríguez-Ruiz et al. (32), who also found significant differences in the DM between men and women professional volleyball players.

Nevertheless, FKs present a 34.8% more of DM in their trapezius (p = 0.01; d = 1.35) than FNKs. These results could suggest a lower muscular stiffness in FKs, which is striking, because it does not agree with the suggestions of Ackland et al. (1) to note the high proportion of muscular mass in top-level kayakers.

However, DM is also related with neuromuscular fatigue (15,16,22), and even DM was effective in detecting muscle damage (19), so another reasonable explanation, given also the highest TC and TD, is that FKs present some local neuromuscular fatigue in their trapezius, as the DM although decrease their values, increasing the stiffness, after an interval effort (15), also tends to increase their values in the requested muscles when they have to support great extended efforts, as suggested by García-Manso et al. (16), in ultra-endurance triathletes, and Smith and Hunter (37). The prolonged effort made by trapezius in isometric contraction, unlike the latissimus dorsi and deltoideus, to favor the efficacy of motor muscles in the stroke, suggests the presence of fatigue accumulated in FKs, probably because of the high volume of training of the cycle carried out before the assessment but should also take into account the order of carrying out of strength exercises in dry, as it is an important variable that determines the effectiveness of strength training (33) (i.e., trapezius muscle fatigue).

In this regard, using TMG, the effect that the 10-day endurance training had on the vastus lateralis of 10 athletes has been detected, observing an increase in TC and DM (20). Besides, the values of MKs are also particularly high in DM (8.0 ± 4.7 mm) and TC (47.8 ± 31.3 milliseconds), which could also correspond in part with this circumstance.

The low lateral symmetry percentage found in FK's trapezius (62.8 ± 17.1%), a 20.4% lower (p = 0.006; d = 1.6) than those of FNKs (83.2 ± 5.4%), and a 19.7% lower than those of MKs (82.5 ± 16.2%), although it was not significant, could support this suggestion. In fact, García-García et al. (14) suggest that an acceptable lateral symmetry percentage, calculated through the software TMG-BMC tensiomyography using the same TMG algorithm, could reach as of 80%. These percentages are similar to those found in the leg muscles of professional road cyclists (82.26 ± 9.84%), which is expected in markedly bilateral and cyclic sports (14).

However, it could be necessary for more assessment throughout the season to observe the behavior of the top-level kayakers' trapezius, in the different training cycles, as the neuromuscular indicators of top-level kayakers evolve over the different training cycles, as indicated by García-Pallares et al. (18).

The differences found by TMG assessment between FKs and FNKs suggest that the specific training to which FKs are subjected has an influence on the contractile properties of the main muscles involved in the stroke, and they would be added up to the findings of other authors to note that top-level kayakers are differed of the general population, by their greater upper body girth and narrow hips (1) and demonstrate superior aerobic and anaerobic qualities (28,45).

In conclusion, TMG has established a neuromuscular profile of muscles that carried out a great effort in stroke of top-level FKs. This profile does not seem to differ substantially from the neuromuscular profile, which top-level men kayakers have shown, so that gender does not seem to have a great influence. However, the specific training that top-level FKs are subjected seems to exert a significant influence on the neuromuscular profile regarding FNKs. The TC has been shown as the clearer parameter to determine this influence. The trapezius are the muscles that have shown the influence of the specific training in FKs.

Practical Applications

They have been established reference values of the main muscles implied in paddling of top-level FKs in recovery period that could serve as a reference for coaches to carry out neuromuscular and of the lateral symmetry monitoring of their kayakers in these periods using a technique that is portable, noninvasive, and does not cause fatigue as with stress testing, so it does not alter the periodization of training.

The coach could use the TMG along with other functional tests for assessing, especially, the trapezius, since they are the muscles that more have shown the influence of the specific training in FKs, its function as stabilizers of stroke to get an effective technique throughout the test, seems to subject them to a load, which could trigger a greater fatigue that in other muscles involved in stroke. This fact suggests that in the dry practice, the trapezius should receive more attention, the coaches can develop specific strength exercises in isometric contraction that prepare them for the important effort that must carry out during the competition and go back to pay special attention to their recovery of important fatigue that seem to show carrying out a specific recovery work that allows a necessary download postexercise.

With data from TC, TD, and DM, the coach would have more information to individualize the load, controlling the training effect or neuromuscular fatigue in kayakers along the season.

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Keywords:

kayak; muscle imbalance; lateral symmetry; training effect; muscle strength

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