HIIT your physiological target in sprint kayak

A logical approach to physiological targeting with HIIT is well described throughout HIIT Science. We know that development of our biological targets (aerobic, anaerobic, neuromuscular) can be stimulated with the right type of training, alongside alignment with the particularities of our context (e.g. athlete profile, sport demands, environmental constraints). This is the bird’s eye view that the coach will want to take to form their decisions regarding HIIT prescription. Most sports we play have a high demand for aerobic energy, so HIIT is often used to develop its capacity¹.  We can investigate the aerobic system by measuring the body’s oxygen consumption during exercise. In particular, we like to know the maximal capacity of this system, termed VO₂max, as it is often a key predictor of endurance performance². VO₂max has both central and peripheral components (Figure 1). Central components refer mainly to the cardiac output, or the heart and lungs’ ability to deliver O₂ to the exercising muscles, and often we find this to be the main determinant of VO₂max within the context of many endurance sports³. Peripheral components refer mainly to the muscles’ ability to extract and use the delivered O₂ (Figure 1). To gain insight into the peripheral VO₂ component, technological advancements in the form of a non-invasive method called near-infrared spectroscopy (NIRS) have arisen. NIRS can be used to non-invasively estimates a muscle’s oxygenation level by measuring the light refraction level at a muscle bed’s periphery (Figure 2)⁴. Due to the relatively smaller upper-body muscle mass associated with sprint kayak⁵, it has been suggested that the peripheral O₂ component may be the stronger determinant of performance versus central aspects per se (Figure 1)⁶. While much research has described the refining of HIIT sessions to improve VO₂max via central adaptations, relatively less research has examined peripheral VO₂ targeting with HIIT. In terms of attempts to maximize the central VO₂ component, time during a HIIT session spent near VO₂max (T@VO₂max; Figure 1) has been the focus for attempting to improve the marker⁷. Similarly, we hypothesized that a session inducing large fluctuations of peripheral muscle oxygenation, measured via NIRS would be an effective means for targeting peripheral adaptations. In our recently published open-access study, we compared the peripheral O₂ response across 4 different HIIT sessions, in order to gain insight into those that would have the potential to maximally induce peripheral deoxygenation, and inferred subsequent resulting adaptations. Our HIIT sessions included two short interval sessions (HIIT-15: 15s/15s and HIIT-30: 30s/30s effort/rest durations), a sprint interval training session (SIT: 6 x 30s/4min30) and a hybrid session, involving long all-out intervals (HIIT-60: 6x1min/3min). All sessions were performed by trained kayakers or canoeists, on a kayak or canoe ergometer (see Table 1). Table 1. Session name with descriptive details used for the study.

Session name	Session description
HIIT-15	2 sets of 20 x 15s at 110% PPO, 15 s at 30% PPO, 5 min rest between sets
HIIT-30	2 sets of 10 x 30 at 110% PPO, 30 s at 30% PPO, 5 min rest between sets
HIIT-60	6 x 1min at 130% PPO, 4 min rest (active or passive)
SIT	6 x 30s all-out, 4min30 rest (active or passive)

  Main results Let’s begin by having a look at the central response across these varied HIIT sessions, in terms of the accumulated time at a near-maximal cardiac output and maximal heart rate (Table 2). Table 2. Central response during HIIT

Session	HIIT-15	HIIT-30	HIIT-60	SIT
	8.1 ± 6.2*	6.8 ± 4.6*	4.1 ± 1.7	1.7 ± 1.3
Cumulated time near maximal cardiac output (min)	5.6 ± 4.4*	4.0 ± 2.9*	2.0 ± 1.9	1.5 ± 1.6
Cumulated time near maximal heart rate (min)	16.6 ± 2.6*$	13.7 ± 3.3*$	5.3 ± 2.3	3.6 ± 1.5

^$different from HIIT-60 (p<0.05), *different from SIT (p<0.05) In alignment with the teachings from Chapter 3 of HIIT Science, short-interval HIIT sessions (HIIT-15, HIIT-30) accumulated the greatest T@VO₂max, heart rate near max and cardiac output near max, suggesting that such sessions clearly stress the central aerobic component. The HIIT-60 session (short HIIT / SIT hybrid) induced substantial T@VO₂max, but a less amount than the short HIIT sessions. The logical conclusion of course is that short interval training is going to be effective HIIT when the primary goal is to induce central adaptations. Let’s now have a look at the peripheral responses to these sessions (Figure 3, Table 3). Table 3. Peripheral response during HIIT in terms of the accumulated time at more than 90% of maximal deoxygenation in the biceps brachii (BB), latissimus dorsi (LD) and vastus lateralis (VL).

Session	HIIT-15	HIIT-30	HIIT-60	SIT
Cumulated time > 90 % deoxy max BB (s)	7.5 ± 8.6*	24.7 ± 40.5	24.5 ± 26.8	44.8 ± 40.0
Cumulated time > 90 % deoxy max LD (s)	8.7 ± 15.3*	29.9 ± 24.9	33.3 ± 37.3	61.2 ± 44.8
Cumulated time > 90 % deoxy max VL (s)	0.0 ± 0.0*	0.2 ± 0.6*	26.5 ± 39.0*	83.2 ± 63.1

*different from SIT (p<0.05) As we might expect, again from our HIIT Science material (Chapter 3), the SIT session was the only session that induced severe and sustained muscle deoxygenation in the locomotor muscles, suggesting this session substantially stresses the peripheral component of the aerobic target of importance to sprint kayakers. In contrast, our short HIIT sessions only induced mild deoxygenation levels, sustained for < 30 sec, and therefore would be considered less of an appropriate stimulus to induce peripheral adaptations. The HIIT-60 session induced a high, but not severe, muscle deoxygenation. Practical takeaways for sprint kayak coach and science teams

1. Coaches and athletes who wish to improve the central component of VO₂max should prescribe short (and long) intervals in their program.
2. Assuming that sustained muscle deoxygenation in training is associated with improved peripheral adaptations, then SIT sessions should be chosen to specifically target the peripheral component. These sessions are of interest especially for upper-body dominant sports such as sprint kayak, and additionally other sports that use relatively-small active muscle masses.
3. Longer supramaximal intervals could be used to maintain both central and peripheral adaptations or to train these components in lower-level athletes.
4. What hasn’t been touched on in this short blog, of course, is the second key physiological target, the anaerobic glycolytic response, and for more insight into maximizing this related and important parameter, the reader is directed to HIIT Science Chapters 3-5.

Conclusion In conclusion, this study extends on the current list of sports within HIIT Science that can benefit from targeted HIIT programming, and in particular, we focussed on the central and peripheral aerobic components. Coaches of sprint kayak athletes need to choose their HIIT weapon accordingly before their athletes hit the water! About the authors: Myriam Paquette is a sport physiologist at the Institut National du Sport du Québec, working primarily with the para cycling and para swimming national teams. Myriam is completing her PhD at Université Laval, under the supervision of Dr Billaut and co-supervision of Dr Bieuzen. Follow her on Facebook.   Dr François Billaut is a full professor of exercise physiology at Université Laval where he leads a sports science research program investigating the acute and chronic effects of HIIT and hypoxia on athlete performances. He is also an applied sport scientist for several Canadian national teams.   References 

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4. Ferrari M, Muthalib M, Quaresima V. The use of near-infrared spectroscopy in understanding skeletal muscle physiology: recent developments. Philosophical transactions Series A, Mathematical, physical, and engineering sciences 369(1955):4577-4590, 2011.

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6. Paquette M, Bieuzen F, Billaut F. Muscle Oxygenation Rather Than VO₂max as a Strong Predictor of Performance in Sprint Canoe-Kayak. Int J Sports Physiol Perform 13(10):1-9, 2018.

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