Effects
of High-intensity Training on Performance and Physiology of Endurance
Athletes Carl D Paton, Will G Hopkins Sportscience 8, 25-40, 2004
(sportsci.org/jour/04/cdp.htm)
Analysis of
Physiological Effects |
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Endurance
in relation to athletic performance has been defined in various ways. In this
article we have reviewed effects of high-intensity training not only on athletic
endurance performance but also on underlying changes in the aerobic energy
system. Endurance for our purposes
therefore refers to sustained high-intensity events powered mainly by aerobic
metabolism. Such events last ~30 s or more (Greenhaff and Timmons, 1998). Training
for endurance athletes generally emphasizes participation in long-duration
low- or moderate-intensity exercise during the base or preparation phase of
the season, with the inclusion of shorter-duration high-intensity efforts as
the competitive phase approaches. The effects of low- to moderate-intensity
endurance training on aerobic fitness are well documented (see Jones and Carter, 2000 for
review), but reviews of high-intensity
training on endurance performance have focused only on describing the effects
of resistance training (Tanaka and Swensen, 1998), the effects of resistance
training with runners (Jung, 2003), and the different types of
interval training used by athletes (Billat, 2001a) and studied by researchers (Billat, 2001b). Furthermore, previous reviews
have included the effects of high-intensity training on untrained or
recreationally active subjects, so findings may not be applicable to
competitive athletes. The purpose of this review was therefore to describe
the effects of high-intensity training on performance and relevant
physiological characteristics of endurance athletes. We
identified most relevant publications through previous reviews and our own reference
collections. We found 22 original-research peer-reviewed articles that
identified competitive endurance athletes as the subjects in a study of
effects of high-intensity training on performance or related physiology. We excluded studies of recreationally
active subjects or of subjects whose characteristics were not consistent with
those of competitive athletes, including Daniels et al. (1978), Hickson et al. (1988), Tabata et al. (1996), Franch et al. (1998), and Norris and Petersen (1998). We did not perform a systematic search of
SportDiscus or Medline databases for theses or for non-English articles, and
we did not include data from chapters in books. We
assigned the training to two categories: Resistance training: sets of explosive sport-specific movements against added resistance, usual or traditional weight training (slow repeated movements of weights), explosive weight training, or plyometrics and other explosive movements resisted only by body mass (Table 1). Interval training: single or repeated intervals of sport-specific exercise with no additional resistance (Table 2). Classification
of some resistance-training studies was difficult, owing to the mix of exercises
or lack of detail. In particular, all
the studies we classified under explosive sport-specific resisted movements probably included some
non-explosive resisted movements and some plyometrics. We classified the duration and intensity of intervals in Table 2 as follows: supramaximal (<2 min), maximal (2-10 min) and submaximal (>10 min), where "maximal" refers to the intensity corresponding to maximum oxygen consumption (VO2max). The supramaximal intervals will have been performed at or near all-out effort; the maximal intervals will have started at less than maximum effort, but effort will have approached maximum by the end of each interval; the submaximal intervals can be considered as being close to anaerobic threshold pace (a pace that can be sustained for ~45 min), and effort will have risen to near maximum by the end of each interval. A major concern with all but one of the
studies we reviewed is that the high-intensity training interventions were
performed in the non-competitive phases of the athletes’ season, when there
was otherwise little or no intense training. Authors who have monitored
endurance athletes throughout a season have reported substantial improvements
in performance and changes in related physiological measures as athletes
progress from the base training to competitive phases (Barbeau et al., 1993; Lucia et al., 2000; Galy et al., 2003). Indeed, our own unpublished observations show that well-trained
cyclists ordinarily make improvements in power output of ~8% in laboratory
time trials as they progress from base through competitive phases of their
season. The large improvement in performance as the competitive phase
approaches occurs because athletes normally include higher intensity
endurance training as part of a periodized program. It therefore seems
unlikely that the large improvements reported in studies performed during a
non-competitive phase would be of the same magnitude if the studies were
performed in the competitive phase, when the athletes ordinarily include
higher intensity training in their program. Indeed, in the only training
study we could find performed during the competitive phase of a season,
Toussaint and Vervoorn (1990) found that 10 weeks of sport-specific resistance training improved
race performance time in national level competitive swimmers by ~1%. Though
such improvements appear small, they are important for elite swimmers (Pyne et al., 2004), and the estimated change in power of ~3% is certainly greater than
the ~0.5% that is considered important in other high-level sports (Hopkins et al., 1999). Analysis of Performance Measures
of performance in real or staged competitions are best for evaluating the
effects of training interventions on competitive athletes (Hopkins et al., 1999). Toussaint et al. (1990) were the only researchers to
use competitive performance in a study of high-intensity training. The others have opted instead for
laboratory-based ergometer tests or solo field tests, which may not reproduce
the motivating effect of competition. Appendix 1
summarizes the effects from sport-specific time trials and constant-power
tests, sorted into the same three intensity/duration categories as the
interval training. Appendix 2 summarizes the effects
on maximum power in incremental tests.
To permit comparison of effects, we have converted outcomes in the
various performance tests into percent changes in mean or maximum power,
using the methods of Hopkins et al. (2001). Footnotes in the
appendices indicate which measures needed conversion. Analysis of Physiological Effects The
remaining tables show the effects of high-intensity training on physiological
measures related to endurance performance: maximum oxygen consumption (VO2max, Appendix 3), anaerobic threshold, exercise economy (Appendix 4), and body mass (Appendix 5). Most endurance events are performed at a
nearly constant pace, and for those performed at an intensity below VO2max mean
performance power or speed is the product of VO2max, the fraction of VO2max
sustained, and aerobic energy economy (di Prampero, 1986). Provided they can be measured
with sufficient precision, percent changes in each of these components are
therefore worth documenting, because they translate directly into percent
changes in endurance power. Of course,
training is likely to change more than one of these components, so
researchers serious about identifying the mechanism of a change in
performance should assess all three. Most
authors of the studies we reviewed measured VO2max, usually in an incremental
test. Some also measured economy (work
done per liter of oxygen consumed) from VO2 measurement either in middle
stages of the incremental test or at a fixed work rate in a separate
test. Where necessary, we re-expressed
percent changes in VO2max and economy for VO2 measured
in units of L.min‑1, to avoid difficulties in interpretation
arising from changes in mass when VO2 is expressed as ml.min‑1.kg‑1. No
authors measured the fraction of VO2max sustained in the endurance
test itself (requiring measurement of VO2 throughout the test), but some
measured the anaerobic threshold, usually from an analysis of blood lactate
concentration during an incremental test.
Depending in its method of measurement, the anaerobic threshold occurs
at ~85% of VO2max, an intensity that an athlete can sustain for ~30-60 min (Jones and Carter, 2000). One can therefore assume that percent
changes in the anaerobic threshold will translate directly into percent
changes in fractional utilization of VO2max in a sub-VO2maximal
event. Authors in two studies provided
the anaerobic threshold as a power rather than a percent of VO2max; in this form the measure is effectively
already a nett measure of submaximal endurance performance, with
contributions from VO2max, fractional utilization of
VO2max, and economy. We therefore
included these measures in Appendix 1 in the subgroup
of submaximal tests. The
relevance of changes in anaerobic threshold to changes in endurance performance
at maximal and supramaximal intensities is unclear, but for such events
(lasting up to ~10 min) anaerobic capacity makes a substantial contribution
to performance (Greenhaff and Timmons, 1998). None of the studies we
reviewed included critical-power or other modeling of performance to estimate
the contribution of changes in anaerobic capacity resulting from
high-intensity training. However, a
practical and much more reliable measure of anaerobic capacity is performance
in sprints lasting ~30 s, which we have included as supramaximal tests in Appendix 1. Body
mass is an important determinant of performance in running The outcomes from individual studies are shown in Appendices 1-5, at the end of this article. Table 3 represents a summary derived from the appendices and justified in the following sections.
Appendix 1 shows that maximal and supramaximal intervals
produced equally impressive gains (3.0-8.3%) on performance at submaximal
intensities. The magnitude of the
largest improvement (Westgarth-Taylor et al., 1997) is likely to be due to either
sampling variation or a computational error, because it is not consistent
with the smaller gains (4.6 and 8.3%) in two similar studies by the same
group (Lindsay et al., 1996; Weston
et al., 1997). Explosive resistance training
was less effective (0.3 and 1.0%) over the same time frame as the interval
training studies (~4 wk), and even after 9 wk the gains were still not as
great (2.9 and 4.0%) as with interval training. In the only study of the effect of usual
weight training on submaximal endurance, there were opposing effects on
anaerobic threshold power (2.6%) and time-trial power (‑1.8%) in the
same subjects after 12 wk. The authors suggested that the non-specific
movement and speed of the weight training accounted for its failure to
enhance time-trial performance (Bishop et al., 1999). Explosive
sport-specific movements produced the greatest gains in maximal endurance
tests (1.9-5.2%) after 8-9 wk (Appendix 1). Maximum intervals were less effective
(2.8%), although the duration of training was only 4 wk. Plyometric jumps were less beneficial
(1.2%). Not
surprisingly, the highest-intensity training produced the greatest
enhancements in the supramaximal tests (Appendix 1). The very large gain with explosive weights
(11%) was more than twice that with supramaximal intervals and explosive
sport-specific resistance (3.0-4.6%).
Maximal intervals had little effect (0.4%). There
was only one study of the effects of submaximal intervals (Sjodin et al., 1982), and it did not include
measures of performance power. The
effects on VO2max, anaerobic threshold, and
economy in that study, if they were additive, would be consistent with ~6%
enhancement of submaximal endurance and possibly 2-4% on supramaximal and
maximal endurance respectively. Maximum-intensity
intervals appear to be the most effective form of high-intensity training for
improving maximum incremental power (by 2.5-7.0%; Appendix
2). Gains appear to be smaller with explosive sport-specific resistance
training (2.3% and 6.0%) and supramaximal intervals (1.0-4.7%), and possibly
smaller still with explosive weights (2.0%).
Remarkably, a gain of 4.7% was achieved in only four sessions of
supramaximal intervals (Laursen et al., 2002a). These
improvements will transfer to time-trial performance to some extent, because
maximum power achieved in an incremental test correlates well with time-trial
performance (Noakes et al., 1990; Hawley
and Noakes, 1992; Bourdin et al., 2004). Exactly how they will transfer might depend
on the duration of the time trial.
Most of an incremental test is performed at submaximal intensities,
but the last minute or two is maximal and supramaximal. Performance in the test will therefore be
determined by a mix of VO2max, anaerobic threshold,
economy, and anaerobic capacity. If
the mix does not reproduce that of the time trial, enhancements of one or
more components of the mix will produce changes in maximum incremental power
that differ from those in time-trial performance. It is
evident from Appendix 3 that the largest improvements
in VO2max occurred with maximal-intensity interval training (gains of
2.3-7.1%). Supramaximal intervals were probably less effective (impairment of
0.6% in one study, enhancements of 2.2% and 3.5% in two others). The changes can occur rapidly: Laursen et
al. (2002a) recorded an increase of 3.5%
after a total of only four supramaximal sessions in two weeks. Explosive
weight training can produce smaller gains (up to 2.0%), but the various forms
of resistance training had a predominantly negative effect on VO2max. Improvements in other physiological
measures can offset this effect and result in nett improvements in endurance
performance following resistance training. One
cannot draw a firm conclusion about the effect of explosive resistance
training on the anaerobic threshold in Appendix 4,
given that there were major enhancements in three studies (5.0-7.1%) and substantial
impairments in two others (2.0 and 2.1%).
In the only study of presumably maximal intervals, the gain was ~5.0%,
whereas the gain was less (1.5%) in the only study of submaximal intervals. Although
the claim of 39% increase in economy from explosive sport-specific resistance
training in Appendix 4 is almost certainly erroneous,
it is clear from the other studies in the table that explosive resistance
training in general produced spectacular beneficial effects (3.5-18%) on this
endurance parameter. Plyometrics may
be only a little less effective (3.1-8.6%).
The effects of interval training were least for submaximal (2.8%) and
greater for a mixture of submaximal and maximal (6.5%). It is
reasonably clear from Appendix 5 that explosive
resistance training increased body mass by ~1%, presumably via an increase in
muscle mass. Any direct harmful
effects of this increase in mass on performance were inconsequential, given
the large enhancements that this form of training produced in power output of
all durations. Usual weight training
may produce increases in body mass that are greater (2.8% in one study) and
therefore more likely to impair performance in some sports. Conclusions and Training Implications High-intensity interval and resistance
training in an endurance athlete’s non-competitive phase can substantially
improve performance and related physiological measures. Interval training at
intensities around VO2max (intervals lasting 2-10 min) improves mainly submaximal endurance
performance (by ~6%) through improvements of all three components of the
aerobic system (VO2max,
anaerobic threshold, economy). Effects of longer intervals at lower intensity
have unclear but possibly similar effects on performance, judging by their
effects on the components of the aerobic system. Higher intensities of interval training
(intervals of <2 min) probably have similar benefit for submaximal endurance
and possibly less benefit (~4%) for shorter durations of endurance
performance, but the contribution of aerobic components is unclear. Explosive
resistance training produces some benefit (~2%) for submaximal endurance, but
probably more benefit (4-8%) for maximal and supramaximal endurance. The effects of explosive resistance
training are mediated at least partly by major increases in economy, possibly
by increases in anaerobic threshold, but probably not by increases in VO2max. Increases in body mass with this kind of
resistance training are not an issue. Many
high-level endurance athletes will already include high-intensity intervals
in their training leading up to and including the competitive phase. For these athletes adding more intervals is
not necessarily a good strategy, but altering the mix to reduce the volume of
lower intensity intervals and increase the volume of higher intensity
intervals may be beneficial. Athletes who do not currently include
sport-specific explosive resistance training are almost certain to experience
substantial gains in performance by adding this form of training to their
programs. A
partially selective effect of the different kinds of training on
physiological measures raises the possibility of prescribing training to
correct weaknesses in these measures.
On the basis of the existing research one can tentatively recommend
adding or increasing explosive resistance training for an athlete with a poor
economy and/or poor anaerobic capacity, and adding or increasing maximal
intervals for an athlete with a poor VO2max. We
need more research aimed at filling voids in the matrix of different kinds of
training vs effects on performance and physiology. In particular: We need to know more about the effects of non-specific resistance training (especially plyometrics and usual weights) on performance and some aspects of physiology. The effects of supramaximal intervals on anaerobic threshold and economy need more research. The one study on physiological effects of submaximal intervals needs augmenting with studies that include performance measures. High-intensity sport-specific resistance training of the non-explosive variety has not been investigated other than in the one study that was performed in the competitive phase. This
new research will give us a more complete understanding of how each type of
high-intensity training in isolation affects endurance performance. More importantly, it will give us a better
indication of the possibility of prescribing training to correct deficits in
an athlete's physiological profile. Well-designed studies of individualized
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