Dr.Biol. V.L. Rostovtsev¹
Dr.Hab. V.D. Kryazhev^1
1Federal Scientific Center for Physical Culture and Sports, Moscow

Keywords: energy efficiency, programmed dynamic electrical myostimulation, smart shorts, cross-country skiing, oxygen consumption, distance heart rate, key movement phase

Background. Electrical myostimulation may be defined as the method of muscle activation by electrical impulses. Programmed dynamic electrical myostimulation may be described as its version applicable on the move in a training process. In case of the cross-country skiing sport, the programmed dynamic electrical myostimulation (PEMS) method uses a programmed microprocessor fixed in smart shorts to energize the core muscle group in the key movement phase to improve the movement energy control [1], particularly in cycling, skating and cross-country skiing sports, with the core muscles stimulated in the push-off phase [5]. Energy efficiency may be interpreted as the ability to control the energy demand of the core muscle groups so as to minimize the energy costs. In cyclic sports, energy efficiency may be rated by sub-maximal oxygen consumption or distance heart rate i.e. the distance covered for one heart beat, with distance heart rate = (V, m/ s x 60): heart rate, m/ beats).

Objective of the study was to rate and analyze the skate skiing stride (quadriceps femoris push-off phase) energy efficiency with/ without PEMS.

Methods and structure of the study. We sampled for an experiment 20.3±0.5 year-old 69.4±1.6 kg heavy and 179.6±2.6 cm tall skilled ski racers (n=6) tested with sub-maximal oxygen consumption = 69.4±3.2 ml/ kg/ min rated by Cosmos Venus treadmill. The training workload protocol was complemented by a synchronized gas exchange test data generated by Cortex MetaLyzer II-R2 gas analyzer and processed by Metasoft 3 software [10]. The athletes, upon a prior warm-up, were tested with/ without PEMS while running the treadmill on ski rollers at 3 m/s with the run angles varying from 4% to 10%; and with the heart rate read by Polar H10 M-XXL pulsometer system.  The PEMS equipment included the smart shorts with a portable electrical myostimulation stimulator wired by silicone electrodes to the electrical myostimulation control unit (100Hz frequency, 80V amplitude, 150ms impulse), with the electrical myostimulation impulses synchronized with the key movement phase as provided by Patent of the Russian Federation No. 2546421 [6] and described in [5]. Significance of the differences in the data arrays were rated by the Student's t-test for paired data.

Results and discussion. The test data and given in Table 1 hereunder.

Table 1. Oxygen consumption and heart rate data yielded by skate skiing stride (quadriceps femoris push-off phase) energy efficiency rating PEMS/ PEMS-free tests, M±σ

Note: *р≤0.05

The PEMS tests found the oxygen consumption and heart rate being significantly lower (regardless of the angle) versus the PEMS-free tests.

Figure 1. PEMS/ PEMS-free tests (red and blue, respectively): oxygen consumption at the run speed of 3 m/s

The PEMS tests showed in every of the 4 load steps the oxygen consumption being lower than in the PEMS-free tests, with the oxygen consumption difference of 2.20±0.15 to 4.49 ± 0.17 ml/ kg/ min (p≤0.05), i.e. 4.4-6.7%; and heart rate difference of 3.7±0.8 to 2.3±0.6 beats/ min (p≤0.05), i.e. 2.9-1.3%. It should be noted that every tested athlete rated positively the PEMS running mode. In PEMS-free test, RE averaged 0.152±0.008 to 0.216±0.007 ml/ kg/ m or 3.18-4.51 J/ kg/ m. In PEMS tests, the oxygen consumption per meter was 6.3-4.7% lower (p≤0.05). The distance heart rate in the PEMS tests averaged 1.44-1.09 m/ beat that was 5.2-2.2% higher than in the PEMS-free tests.

Generally the energy efficiency improvement strategies give a special priority to the high-intensity long trainings at the lactate threshold, motor skills improvement and other aspects [7]. In the PEMS-assisted case, the energy efficiency improvement is likely to be achieved by redistribution of the muscle electrical activity and improved skate skiing stride technique biomechanics. As we have demonstrated in our prior studies, PEMS redistributes the energy flows to increase them in the thigh muscles in the push-off phase in speed skating and cross-country skiing sports – and reduce in the electrical activity in the secondary muscle groups [3, 4]. Therefore, the total electrical activity of the muscles in the key movement phase tends to fall to reduce the oxygen consumption, increase the knee joint extension speed, cut down the push-off phase time and, hence, the mechanical work on the whole [2] – to scale down the energy cost per meter as a result. It should be also noted that the energy cost per meter was lower for the roller ski run on the Di Prampero treadmill versus the run exercise (RE = 3.72±0.238 J/ kg/ m) [8] and higher for the steeper ascends.

Conclusion. The study data and analyses showed that the programmed dynamic electrical myostimulation method may be highly beneficial for the instant energy efficiency improvement purposes in the modern skate skiing sport, with the energy efficiency and distance heart rate recommended as highly informative tests rates applicable in the endurance, technical progress and muscle control/ relaxation tests.

References

1. Anokhin P.K. Essays on Physiology of Functional Systems. Moscow: Meditsina publ., 1975, 447 p.
2. Kryazhev V.D. Development, preservation and restoration of human motor abilities. M.: VNIIFK publ., 2002. 247 p.
3. Kryazhev V.D., Skorosov K.K., Kurbakova N.V. Relationship between efficiency of movements and muscle electroactivity level in speed skating. Teoriya i praktika fiz. kultury. 1986. No. 3. p. 13.
4. Rostovtsev V.L. Biological justification of extra-training tools using technology to improve elite athletes’ performance. Doct. Diss. Abstract (Biol.). M., 2009. 45 p.
5. Rostovtsev V.L., Kryazhev V.D. Efforts to improve sports movements based on smart technologies of artificial muscle activation. Vestnik sportivnoy nauki. 2018. No. 1. p. 63.
6. Rostovtsev V.L. Method to control parameters of physical exercise motor stereotype and a device for its implementation: patent No. 2546421. M., 2015.
7. Barnes, K.R., and Kilding, A. E. (2015). Strategies to improve running economy. Sport Med. 45, 37–56. doi: 10.1007/s40279-014-0246-y
8. Di Prampero p. e., c. Capelli, p. Pagliaro, g. Antonutto, m. Girardis, p. Zamparo, and r. g. Soule. Energetics of best performances in middle-distance running. J. Appl. Physiol. 74(S): 2318-2324, 1993.
9. Dolbow D.R., Holcomb W.R., Gorgey A.S. Improving the Efficiency of Electrical Stimulation Activities After Spinal Cord Injury. Curr Phys Med Rehabil Rep. 2014 Jun 18;2(3):169-175. PubMed PMID: 29503764; PubMed Central PMCID: PMC5832057.
10. Wasserman K., Hansen J.E., Darryl Y.S, Casaburi R., Whipp B.J. Principles of exercise testing interpretation. Third Edition. Lippincott Williams & Wilkins. 1999. 354 p.

Corresponding author: rost.177@yandex.ru

Abstract

Objective of the study was to rate and analyze the skate skiing stride (quadriceps femoris push-off phase) energy efficiency with/ without programmed dynamic electrical myostimulation.

Methods and structure of the study. We sampled for an experiment 20.3±0.5 year-old 69.4±1.6 kg heavy and 179.6±2.6 cm tall skilled ski racers (n=6) tested with sub-maximal oxygen consumption = 69.4±3.2 ml/ kg/ min rated by Cosmos Venus treadmill. The training workload protocol was complemented by a synchronized gas exchange test data generated by Cortex MetaLyzer II-R2 gas analyzer and processed by Metasoft 3 software. The athletes, upon a prior warm-up, were tested with/ without programmed dynamic electrical myostimulation while running the treadmill on ski rollers at 3 m/s with the run angles varying from 4% to 10%; and with the heart rate read by Polar H10 M-XXL pulsometer system. 

Results of the study and conclusions. It was found that the economical efficiency, estimated by oxygen consumption per meter of track with programmed dynamic electrical myostimulation, was 6.3-4.7% higher than during the usual movement. Distance pulse with programmed dynamic electrical myostimulation (meters covered per a tick of the blood) was 2.2-5.2% higher. It is discussed that the increase in RE was due to the redistribution of the muscle electrical activity and the improvement of the biomechanics of the skating stroke.

The study data and analyses showed that the programmed dynamic electrical myostimulation method may be highly beneficial for the instant energy efficiency improvement purposes in the modern skate skiing sport, with the energy efficiency and distance heart rate recommended as highly informative tests rates applicable in the endurance, technical progress and muscle control/ relaxation tests.