Acute Effect of Uphill Running: Current Scenario and Future Hypotheses

EFEITO AGUDO DA CORRIDA ASCENDENTE: CENÁRIO ATUAL E FUTURAS HIPÓTESES

Strategies for metabolic adjustments are often considered by athletes throughout a running event. Planning for such events during training does not always include variations from level training, even though up/downhill exertion should definitely be a part of such planning. The differentiation of training stimuli, under adverse conditions of intensity and inclination, can generate differentiated benefits. However, uphill running raises expectations of deleterious effects. The imposition of different slope gradients throughout running could generate increased metabolic demands for sports performance. Thus, the present study aimed to answer questions mainly about the acute effects of uphill running, its relationship with aerobic performance, allowing us to introduce new hypotheses for future studies in the area on the subject. Gaps still need to be filled concerning the relevance of uphill running, and its determinants. Many of the points presently under scrutiny only lead to speculative explanations; for logical reasons, more studies should focus on the prescription of training at different slopes. This is the point at which specific conditioning is required, because the regulation of the effort and the energy cost resulting from the imposition of uphill running during competitive races depends heavily on previous experiences. This review will cover recently published research on the subject.

KEYWORDS:
Uphill Running; Kinematic Analysis; Stretching-Shortening Cycle; VO_2Max

RESUMO

Estratégias para ajustes metabólicos são frequentemente consideradas por atletas ao longo de um evento de corrida. O planejamento de tais eventos durante o treinamento nem sempre inclui treinamento em planos inclinados, que deveriam compor esse planejamento. Adiferenciação dos estímulos de treinamento, em condições adversas de intensidade e inclinação, pode gerar benefíciosdiferenciados. No entanto, a corrida ascendente aumenta as expectativas de efeitos deletérios. Portanto, a imposição de diferentes gradientes de inclinação ao longo da corrida poderia gerar demandas metabólicas aumentadas paradesempenho esportivo. Assim, o presente estudo tevecomo objetivo responder questões principalmente sobre os efeitos agudos da corrida ascendente, sua relação com o desempenho aeróbio e a proposição de novas possíveis hipóteses para estudos futuros sobre o assunto. Muitaslacunas ainda precisam ser preenchidas sobre a relevância da corrida ascendente e seus determinantes. Muitas das questões apresentadas apenas levam a explicaçõesespeculativas; por razões lógicas, mais estudos devemse concentrar na prescrição de treinamento em face dediferentes porcentagens de inclinação. Este é o ponto em que o condicionamento específico é necessário, porquea regulação do esforço e do custo de energia resultanteda imposição de corrida ascendente durante corridascompetitivas depende fortemente das experiênciasanteriores.

PALAVRAS CHAVE:
Corrida em Inclinação; Análise Cinemática; Ciclo Alongamento Encurtamento; VO_2Máx

INTRODUCTION

Running performance is influenced by mechanical, physiological, anthropometric, neuromuscular, and environmental factors.^1,2 Therefore, in an already well established manner, gains in one or more of these categories promote greater aerobic competence and better sports performance.^3-7 It has also been reported that in race events, mainly in the middle to long distance range, experienced athletes consciously or unconsciously regulate their "pace" strategy in order to maintain a lower metabolic cost.^8,9 However, with the evolution of racing events, it is essential to re-examine models applicable to the competitive dimension of courses with variations of terrain, including variations positive or negative slopes. Athletes and coaches who once trained/prescribedmore regular "pace" strategies have recently started to include in their programs variations in their own courses,or moved toward using specific training courses withvarying inclinations, which would more adequately reflectreal competitive scenarios. To achieve a much needed competence to minimize metabolic cost during running, differentiation of training stimuli has been introduced. Training in adverse conditions of positive/negativeslopes, or on different surfaces (asphalt, grass, sand) can provide the needed conditions for adaptation and shouldhave a special place in training prescription. Althoughempirical, these variables in turn can generate long-termdifferentiated metabolic and neuromuscular benefits.^10,11

Reports are beginning to delineate the acuteeffects of uphill running, pointing out singular differences relating to the variable inclinations required in training sessions.^12-16 Variable slope uphill running is capable ofimposing different relationships between the application ofconcentric and eccentric forces during the running cycle.¹³ In addition, there seems to be a significant associationbetween concentric overload and the percentage increase of uphill running distances; consequently, more attention has been given to this modality. Sloniger et al¹⁶ observed a 9% higher muscle activation at a 10% inclination running, compared to flat running. This increased muscle activation is in line (a) with the greater relative contribution of the concentric force observed during uphill activity, (b) with a significantly higher metabolic cost,^17,18 and (c) with apattern of differentiated muscular recruitment.¹⁶

Positive chronotropic modifications and theheightened development of the slow component of oxygen consumption complete the list of significant physiological changes resulting from slope training.^17,19,20 It seems that the behavior of these variables shows greater amplitude during running long stretches at unusually intense slopes, when compared to running in the plane. Possibly suchacute physiological changes can be attributed to excessive muscular overload coming from the major concentriccomponent of muscle contraction.¹³ The reduced use of the elastic power mechanisms and stretching-shortening reflexes could also partly explain this differentiatedmanifestation between concentric vs. eccentric moment, but some aspects still remain in the field of speculation.^20,21 Thus, the present study aimed mainly to answer questions about the acute effects of uphill running, its relation with aerobic performance, and the proposition of new possible hypotheses for future studies in the area.

METHOD

An search was performed ending September 2017. Articles with the key words "Uphill Running", "AerobicExercise", "Stretching-Shortening Cycle", "VO_2Max" were searched in the databases of PubMed and Web of Science. Within this context, articles that discussed the acute effects of uphill running, its relationship with aerobic performance,and new possible hypotheses for future studies on thesubject were selected. Only articles in English and focused on the theme were included.

RESULTS AND DISCUSSION

Acute Physiological Changes and Their Perspectives

Pringle et al.¹⁹ reported higher VO_2Max values in horizontal and uphill maximum progressive protocols (3.84± 0.57 L/min [0% slope] and 3.95 ± 0.60 L/min [10% slope], respectively). This had already been shown by Olesen et al.¹⁴ and could be attributed to higher content of motor units being recruited during the uphill running. This assumptionis based on the fact that in the horizontal plane the eccentricphase of the movement is enhanced, adequately activating stretch reflexes. This, coupled with an adequate elasticpotential accumulation, leads to a lesser need for activationof motor units, resulting in a lower metabolic cost for force production.^22,23 In addition, during a maximal stress testthe amplitude of the slow component at a 10% inclination VO₂ was 40% higher than the corresponding value for a flat exercise.¹⁹

During submaximal running exercise sessions,Padulo et al¹⁵ reported a reduced R-R interval for a running test for 5 min at 2% inclination, compared to that observed in the horizontal plane (0.388 ± 0.02 vs. 0.327 ± 0.05 ms, for 0% and 2% inclination respectively). This represented an increase of 5% in heart rate, associated with a 10%increase in VO₂. In steeper uphill running conditions (7% incline at 70% of V_VO2Max), the reduction in the R-R interval was more pronounced for the same 5 min run (0.388 ± 0.02 ms on the flat vs 0.280 ± 0.05 ms, for a 7% slope). This translates to 15.1% increase of heart rate with a 19% increase of submaximal VO₂.¹⁵ Similar results were observed by Klein et al,²⁴ in high performance athletes submittedto a 35 min run at a 5% slope: they exhibited increasesof heart rate (11%), VO₂ (18%), respiratory exchangerate (8%), and minute ventilation (24%). Other evidence corroborates this outcome, highlighting the amplitude of the physiological effects slope-dependent, or percentage-dependent procedures.^16,25

Uphill Running and the Determinants of Performance

Intense acute effects on aerobic performance areobserved in the running on the inclined plane. As already mentioned, the concentric contribution is proportionalto the degree of inclination;¹³ It is also associated with a reduction in the potentiating effects of the stretch-shortening cycle. Consequently, the metabolic energy spentto achieve the same velocity is higher in the uphill thanin the horizontal plane. Reduced yield observed duringuphill running can be explained in part by mechanical and kinematic alterations,²⁶ which are revealed as changes of the physiological profile. In fact, the are many determinantsof aerobic performance, and perhaps the neuromuscular contribution is of greater importance when running upa slope than other factors. However, this still needs to be properly investigated.²⁷

Swanson and Caldwell²⁸ have suggested an importantrole of running economy reflecting negatively on the uphill running performance. It seems that changes above orbelow the optimum kinematic pattern exerts deleterious influences, increasing metabolic cost and perceived exertionin uphill running.²⁸ Snyder and Farley²⁹ reported a U-shaped pattern in the frequency ratio of past metabolic cost,suggesting mechanical inefficiency at low pass frequencies,and higher cost associated with the production of forceat high pass frequencies, hence a worsening which isultimately detrimental to economy.

The decline in running performance is also notable in maximum progressive tests (V_VO2Max = 18.7 ± 1.9 km/h and 14.0 ± 1.6 km/h, respectively for 0% and 10% slope); running economy certainly influences the outcomes insuch tests.¹⁶ However, other factors such as (a) morepronounced and early activation of the anaerobic energy system, (b) a greater oxygen deficit, (c) a larger amplitude in the slow component of VO₂, and possibly (d) a precociousoccurrence of the lactate threshold, would limit the total exercise time and the obtained VO_2max. Paradoxically, the highest values of VO_2Max are observed at high percentages of uphill running.^14,19 Finally, considering the well-known predictive value of VO_2max on medium and long-term aerobic performance,⁴ it remains to be determined whether the same predictive behavior is observed in the VO_2max obtained in high slope condition.

Acute Deleterious Mechanisms in Uphill Running

During the initial phase of running in the horizontal plane, it is believed that only part of the work requiredis performed by the contractile elements,³⁰ while the remainder comes from the elastic elements and intrafusal reflexes of the musculature.³ The stretch-shortening cycleis directly tied to the concept of energy conservation duringrunning; however, it is possible that that the contribution of elastic elements and of yet unestablished reflexes onthe inclined plane might be suppressed,^13,28 overloadingthe skeletal muscle structure. Therefore, the absorption of elastic energy at the moment of entry of the calcaneus and support phase, and consequently the transfer ofthis energy for the enhancement of movement does notoccur satisfactorily. Kinematic changes partly explain the deleterious effect on running performance on the inclined plane, where significant increases of contact time areobserved and are generally proportional to slope intensity.²⁶ Table 1 shows the main modifications in uphill running. Thus, part of the produced energy is lost in the form of heat. The degree of contribution of the reflex mechanisms is not clear enough, but it is also estimated that the energy requirement to move the center of mass vertically during uphill running is greater than on the horizontal plane and proportional to the degree of inclination imposed uponthe practitioner.

Table 1
Kinematic, postural, and performance variations in uphill running, and in different planes.

				Outcomes
Authors	n	Running	Gradient (º)	Performance	Postural Angular Variation (º)					Kinematic Variation
				Maximal Speed (km.h-1)	Trunk (T/O)	Hip (T/O)	knees (T/O)	Thighs (T/O)	Ankles and Ground (T/O)	Time Contact (ms)	Flight Time (ms)	Frequency of Stride (Hz)	Time to Stride (ms)	Lenght of Stride (m)
28	8	Sprint	+3	28* (-3%)	(73*/74,0*) (-9%/10%)	(129/196)	(144/158*) (-4%)	(31*/101,0) (74%)	(88*/37,0*) (-5%/-14%)	133	124	3.90	257'	2.00* (-5%)
			-3	31.6* (9%)	(82/82)	(136*/200) (4%)	(155*/155*) (6%/-6%)	(40*/99,0) (35%)	(100*/37*) (8%/16%)	131	127	3.88	258	2.26* (7%)
			0	29	(80/82)	(131/204.0)	(145/165)	(54/99)	(92/43)	138	127	3.79	265	2.11
33	9	Sprint	+3	22.6* (-20%)	NM	(47.1/95.8)	(143.4* /159.4) (4%)	NM	(96.2/103.9)	137.0* (15%)	132.0	3.90* (7%)	NM	1.82* (-16%)
			0	27.2	NM	(55.3/95.9)	(149.4/151.6)	NM	(102/ 104.5)	117.0	128.0	3.61	NM	2.12
13	10	Submax Running	+3/+6º/+9	NM	NM	NM	NM	NM	NM	23/23/23	NM	1.46/1.49/ 1.51* (5%)	NM	2.07/2.02/1.99* (-4%)
			-3/-6/-9	NM	NM	NM	NM	NM	NM	23/22/22	NM	1.43/1.42/1.42	NM	2.10/2.12/2.12
			0	NM	NM	NM	NM	NM	NM	23	NM	1.45	NM	2.07

• (T/O) – ground touch phase / ground output phase; (º) – unit in degrees; (ms) – milliseconds; NM – not measured;
• ^*
  significantly different from running in the horizontal plane.

Hypothetical Advantages of Uphill Running

Some advantages can be explored as functions ofuphill running. Initially, it must be noted that if a highmechanical impact generated on the human body with eachdeveloped stride becomes a negative factor, it makes joints and muscles more vulnerable to the incidence of injury. However, the behavior of the ground reaction force in uphillrunning is inversely proportional to the required degree of elevation.¹³ Thus, the muscular and articular requirement for absorption of mechanical loads is reduced and possibly keeps the contractile components and reflexes intactfor longer. In another perspective, Roberts & Belliveau³¹ have suggested that due to a preponderant concentricmuscular solicitation, and because of the increased work load associated with uphill running, the overload on the knee joint is reduced, and in turn more work would occur on the hip and their extensors.³¹ Perhaps the slope artifice can be visualized as a functional mode of knee joint post-injury re-conditioning.³¹ As a final point, considering the contemporary demands of performing race tests, it is clear that there is a need for specific conditioning in different inclinations. In this way, it is possible to speculate about theexistence of some mechanism of a transfer of adaptations resulting from uphill running to flat race performance.^10,11 Such effects could be beneficial to sports performance and deserve to be properly investigated.

FINAL CONSIDERATION

The acute effects of uphill running are alreadyreasonably delineated in the literature. However, thedeleterious physiological and mechanical mechanisms thatdirectly influence the determination of putative influences upon aerobic performance are not well understood. Many ofthe present-day questions have only received explanations of a speculative nature. Logical reasoning suggests thatmore studies should focus upon the prescription of uphill training, before different percentages of inclination areembarked upon. In spite of these findings, the need forspecific conditioning is obvious: the regulation of effort andenergy cost in uphill running depends heavily on previous experiences.

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Publication Dates

• Publication in this collection
  2018

History

• Received
  05 Nov 2017
• Reviewed
  25 Nov 2017
• Accepted
  30 Dec 2017