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88 Int. J. Human Factors and Ergonomics, Vol. 6, No. 1, 2019
Copyright © 2019 Inderscience Enterprises Ltd.
The efficacy of rooibos Aspalathus linearis as an
ergogenic aid during exercise
Simeon E.H. Davies*
Department of Sport Management,
Cape Peninsula University of Technology,
Cape Town, 8001, South Africa
Email: daviess@cput.ac.za
*Corresponding author
Jeanine L. Marnewick
Oxidative Stress Research Centre,
Institute of Biomedical and Microbial Biotechnology,
Cape Peninsula University of Technology,
Cape Town, 8001, South Africa
Email: marnewickj@cput.ac.za
Sacha West and Mogammad Sharhidd Taliep
Department of Sport Management,
Cape Peninsula University of Technology,
Cape Town, 8001, South Africa
Email: wests@cput.ac.za
Email: talieps@cput.ac.za
Fanie Rautenbach
Oxidative Stress Research Centre,
Institute of Biomedical and Microbial Biotechnology,
Cape Peninsula University of Technology,
Cape Town, 8001, South Africa
Email: rautenbackf@cput.ac.za
Raeeq Gamieldien
Department of Sport Management,
Cape Peninsula University of Technology
Cape Town, 8001, South Africa
Email: gamieldienr@cput.ac.za
Abstract: This study investigated whether rooibos herbal tea Aspalathus
linearis has an ergogenic effect during a fatiguing arm strength test to
exhaustion. Thirty-two male participants were randomised in a single blinded,
cross-over placebo controlled study in which they ingested standardised
The efficacy of rooibos Aspalathus linearis as an ergogenic aid 89
rooibos or placebo capsules for four weeks prior to a fatiguing elbow
flexion/extension exercise test entailing five sets/bouts of 15 repetitions of
maximum voluntary contractions separated by 10-second rest intervals on a
Biodex System 3 at a speed of 60º per second. Peak torque flexion (Nm) was
consistently higher in the rooibos experimental (Re) compared to the placebo
control (Pc) across the five exercise bouts, and this performance trend during
flexion was also seen in the total work (joules) completed, although not
significant (P > 0.05). It appears that the antioxidant properties of rooibos, may
have contributed to an improvement in physical performance during a maximal
isokinetic arm exercise protocol to induce fatigue.
Keywords: rooibos; antioxidant; exercise; ergogenic supplement.
Reference to this paper should be made as follows: Davies, S.E.H.,
Marnewick, J.L., West, S., Taliep, M.S., Rautenbach, F. and Gamieldien, R.
(2019) ‘The efficacy of rooibos Aspalathus linearis as an ergogenic aid during
exercise’, Int. J. Human Factors and Ergonomics, Vol. 6, No. 1, pp.88–102.
Biographical notes: Simeon E.H. Davies is Professor and the Head of the
Sport Management Department at the Cape Peninsula University of
Technology. He has extensive experience in the field of sport and exercise
science, as well as ergonomics and human factors. He is active in his
professional areas of expertise, which include being a member of the Executive
Council for the Ergonomics Society of South Africa, and the Chartered Institute
of Ergonomics and Human Factors. He is particularly interested in research
concerning sports/exercise science in applied situations, along with
ergonomics/human factors, as well as ethical issues in research.
Jeanine L. Marnewick is a Professor in the Health and Wellness Sciences
Faculty at the Cape Peninsula University of Technology and head of the
Oxidative Stress Research Centre. She has extensive research experience
particularly on the bio-activity two indigenous herbal teas, rooibos and
honeybush and has made important and novel contributions to the scientific
literature. This work has resulted in her being recognised as an expert on
rooibos, nationally and internationally. She started the rooibos research about
18 years ago at the Medical Research Council, looking at cancer
prevention/chemoprevention through rooibos.
Sacha West received her BSc (Med) Hons (Biokinetics) and obtained her PhD
in Exercise Science at the University of Cape Town (UCT) South Africa. She is
a Research Scientist and Lecturer in the Department of Sport Management and
has special responsibility for the Human Performance Lab where experimental
trials are conducted at the Cape Peninsula University of Technology. She has a
specific research interest in the Ecso-Walking suit and persons suffering from
spinal injury, along with rooibos as an ergogenic agent. She has also recently
completed her MPhil in Public Health (UCT).
Mogammad Sharhidd Taliep obtained his PhD in Exercise Physiology at the
University of Cape Town (UCT) South Africa. He is a Senior Lecturer and
Researcher in the Department of Sport Management at the Cape Peninsula
University of Technology. He is particularly interested in high performance
sport and ways in which to optimise playing performance.
Fanie Rautenbach received his MSc in Biochemistry and has been the
Laboratory Manager in the Oxidative Stress Research Centre’s analytical
laboratory for the past 13 years. He specialises in all antioxidant capacity and –
content analyses for the food and beverage industries, while also providing
90 S.E.H. Davies et al.
training for postgraduate students in these assays enabling them to complete
their research studies at the Cape Peninsula University of Technology. He is
also responsible for optimising newly acquired assays.
Raeeq Gamieldien obtained his BTech in Sport Management at the Cape
Peninsula University of Technology (CPUT), South Africa. He is the Lab
Technician in the Human Performance Lab (HPL) where he has special
responsibility for the set-up and implementation of research work. He has been
highly involved in the implementation of studies at the HPL including
head-loading in African females.
This paper is a revised and expanded version of a paper entitled ‘Antioxidant
supplementation and exercise-induced fatigue: rooibos Aspalathus linearis’
presented at 7th International Ergonomics Conference, ERGONOMICS 2018,
Zadar, Croatia, 13–16 June 2018.
1 Introduction
There continues to be considerable debate regarding the effect of antioxidant
supplementation on oxidative stress during exercise in humans. Clarkson and Thompson
(2000) asks the question “Are antioxidant supplements necessary for individuals who
exercise regularly?” This same query may be extended to those occupations characterised
by physical work, especially if the nature of the task is repetitive and likely to cause
fatigue. However, it is clear that much of the research thus far in terms of antioxidant
supplementation for enhanced physical performance has been conducted almost
exclusively within the field of sport and exercise science. This paper takes cognisance of
the increasing importance of ergogenic aids to improve human performance not only in
sport but also for industrial or military applications (Boff, 2006; Eichner, 1997) and
provides an insight into the potential benefits of antioxidant supplementation for
improved exercise performance, by way of an experimentally controlled study.
Kanter (1994) makes the assertion that habitual physical activity promotes a number
of adaptations that have an overall positive effect on the body. Despite the undeniable
health benefits, exercise may increase mitochondrial formation of reactive oxygen
species (ROS) and reactive nitrogen species (RNS), which may cause cellular damage
(Ristow et al., 2009). When produced in excess, free radicals may promote cellular
oxidation, damage in the DNA structure, aging and a variety of diseases (Sahlin et al.,
1985). These result in impaired skeletal muscle function and causes pain and thereby
affects exercise performance (Yfanti et al., 1985). However, the body has some unique
mechanisms to combat the formation of free radicals and other ROS and RNS, notably an
endogenous antioxidant defence system, composed of enzymes, notably catalase,
superoxide dismutase, glutathione peroxidase and glutathione reductase (GR) and
non-enzymatic antioxidants (glutathione) whose major role is to detoxify and/or attenuate
the harmful effects of ROS (Dosek et al., 2007). Furthermore, the endogenous antioxidant
system can be complemented by exogenous antioxidant supplementation, which can also
protect the cells against deleterious effects of ROS, attenuate excess free radicals and
generally maintain redox balance that provides further protection against diseases
(Pham-Huy et al., 2008).
The efficacy of rooibos Aspalathus linearis as an ergogenic aid 91
In an attempt to minimise the effects of oxidative stress during physical activity,
many athletes and sports professionals are taking supplementation with antioxidant(s)
and/or vitamins (Draeger et al., 2014). The reasons for antioxidant supplementation and
in this case, more specifically rooibos, may be based on the understanding that they may
act as an ergogenic aid to improve performance and/or as a functional food to optimise
health and performance (Garthe and Maughan, 2018). A review of literature regarding the
usage of dietary supplements including antioxidants in the general population have
consistently shown that supplements are used by a large part of the population and this is
confirmed by the sales figures of what is now a multi-billion-dollar global industry
(Hämeen-Anttila et al., 2011; Timbo et al., 2006). According to national surveys of the
general population in the United States, more than 40% of the adult population used
dietary supplements in the period from 1988–1994, and this had increased to over
one-half during 2003–2006 (Centers for Disease Control and Prevention, 2011).
Packer (1997) contends that while exercise is known to have many beneficial effects,
there is much evidence that free radical production increases during exercise, and that
oxidative damage occurs in the muscle, liver, blood and perhaps other tissues. By
inference one can assume that habitual physical work, which is arduous and repetitive
may also induce oxidative damage. The nutritional status of the worker has the potential
to influence many work tasks and will therefore impact on the outcomes derived from
ergonomics assessments. However, nutrition is very rarely considered in these
investigations nor its potential to reduce the chronic-disease risk of the worker (Shearer
et al., 2016).
As previously mentioned the field of sports and exercise science has prioritised
research into nutritional strategies to optimise performance and from these investigations
best-practice evidence-based recommendations and position stands have been developed
(Goldstein et al., 2010). It is becoming increasingly apparent that many athletes and
sports professionals are ingesting plant phytochemicals with known antioxidant qualities
in an attempt to minimise the effects of oxidative stress during physical activity,
including rooibos Aspalathus linearis (Marnewick et al., 2011); ginkgo biloba (Rong
et al., 1996); as well as oligomeric proanthocyanidins (OPCs), and polymers of flavanols
found in grape extract (Lafay et al., 2009). Additionally, nutritional antioxidant
supplements such as selenium, vitamin C and E health impacts have been well explored
within an exercise context in attempts to counteract and/or minimise effects of ROS
(Packer, 1997), as well as glutathione (Gohil et al., 1998).
Whilst there is an increasing focus in sport and exercise science research into the
potential benefits of antioxidant supplementation, the field of human factors and
ergonomics has given less consideration to nutraceutical interventions. This is interesting
because Packer (1997) makes the point that antioxidant supplementation may be most
relevant for persons who habitually engage in regular physical work, and the real benefits
from antioxidant supplementation are more likely to occur over the long-term by
minimising the damage as a consequence of exercise-induced free radical increase. This
paper alludes to the potential of rooibos Aspalathus linearis as an effective antioxidant
and ergogenic aid not only during strenuous bouts of exercise, but also for the mitigation
of fatigue in occupations characterised by repetitive physical actions.
92 S.E.H. Davies et al.
1.1 Rooibos – Aspalathus linearis
Rooibos (Aspalathus linearis [Burm.f.] R. Dahlgren, Leguminosae) is a shrubby legume,
which is also referred to as a fynbos plant that is indigenous to the mountainous area of
Clanwilliam in the Western Cape Province of South Africa (Marnewick et al., 2009).
Rooibos is also consumed as a unique herbal tea made from the leaves and stems of this
fynbos plant (McKay and Blumberg, 2007; Joubert et al., 2008; Marnewick et al., 2009).
There is strong anecdotal evidence regarding the use of rooibos prior to the colonisation
of South Africa by Europeans, and historical records indicate its traditional use in the
1700s, furthermore rooibos has been linked to numerous health promoting properties, but
substantiation of these health claims are scarce (Marnewick et al., 2011).
Rooibos is naturally caffeine free and contains very low levels of tannins (Blommaert
and Steenkamp, 1978) when compared to the Camelia sinensis teas, and is known to have
antioxidant qualities. Rooibos therefore is an important dietary source of antioxidants
containing mostly flavonoids, but also the unique C–C linked dihydrochalcone glucoside,
aspalathin (Koeppen and Roux, 1965) and cyclic dihydrochalcone and aspalalinin
(Shimamura et al., 2006). According to Awoniyi et al. (2012) in vivo evidence has shown
that aqueous rooibos extracts are able to modulate oxidative stress by inhibiting lipid
peroxidation and augmenting the glutathione redox status in rat sperm, rat liver (Ajuwon
et al., 2013) and adults at risk of developing cardiovascular diseases (Marnewick et al.,
2011). Immunomodulatory effects of rooibos have been previously reported both in vitro
and in vivo (Kunishiro et al., 2001; Hendricks and Pool, 2010), while the
anti-inflammatory action of rooibos was demonstrated by two of its flavonoids (luteolin
and quercetin), which were able to reduce the secretion of pro-inflammatory cytokine,
IL-6 and TNF-α using a LPS-stimulated macrophage model (Mueller et al., 2010).
A study by Marnewick et al. (2016) profiled a number of oxidative stress biomarkers,
as well as exercise performance indicators to assess the efficacy of an acute dose of
rooibos in altering these biomarkers and performance outcomes. Forty healthy adult male
volunteers were randomised in a single blinded, cross-over placebo controlled study.
They consumed a standardised breakfast snack and an acute dose of antioxidant in the
form of three capsules of a rooibos Aspalathus linearis extract or placebo before
undergoing a muscular isokinetic strength fatiguing trial. Muscle fatigue was induced
using elbow extension/flexion test on the Biodex (15 repeats, 5 sets). The results for
isokinetic strength performance showed significantly increased total work (P = 0.019),
average power (P = 0.021) and average peak torque (P = 0.01) during the 2nd extension
when comparing rooibos with placebo. When considering the blood oxidative stress
biomarkers, rooibos significantly decreased the levels of conjugated dienes at all 5 time
points when comparing with the placebo. Rooibos also significantly enhanced (P < 0.05)
the antioxidant capacity (ORAC) (4–5%). The researchers concluded that an acute dose
of rooibos appears to be protective against exercise-induced oxidative stress, by
minimising the oxidative damage to that of baseline levels possibly due to an enhanced
defence system, and may have contributed to improved exercise markers. Rooibos has
also demonstrably modulated oxidative stress in a work-based study, which involved an
8-week randomised placebo-controlled intervention, which reported on the antioxidant
status of lead factory workers after drinking traditional (fermented) rooibos herbal tea
(Nikolova et al., 2007). Modulation of the redox status of these workers was shown by a
decreased level of lipid peroxidation measured as malondialdehyde (MDA) in the plasma
and an increased level of blood glutathione (GSH). The same authors concluded that
The efficacy of rooibos Aspalathus linearis as an ergogenic aid 93
drinking of rooibos herbal tea showed positive effects on the antioxidants indices,
connected to GSH and thiol-enzymes such as superoxide dismutase (SOD) and
delta-aminolevulinic acid dehydratase (ALA-D). The tendency for reduced lipid
peroxidation suggested that rooibos could play a beneficial role for workers who are
habitually exposed to lead.
1.2 Purpose of the study
The purpose for this study stems from research conducted by Marnewick et al. (2016) in
which the research participants ingested an acute dose of rooibos prior to an isokinetic
elbow extension/flexion test. The present study replicates maximal isokinetic elbow
extension/flexion test, involving five sets/bouts of 15 maximal repetitions, with 10
seconds rest, between sets; however, the participants in the present trial ingested a
chronic dose of rooibos (or a placebo) for four weeks prior to the exercise test.
Marnewick et al. (2016) reported that when the participants supplemented with an acute
dose of rooibos prior to the exercise test their strength performance was significantly
higher. The present study was instigated to gain further insight into the possible benefits
of rooibos ingestion, (in this case a chronic dose over four weeks) and to report on the
modulation of exercise performance during an isokinetic fatigue exercise test. The
rationale for the choice of study design, along with the population, was based on the view
that elevated oxidative stress induced by maximal exercise may be required for clear
detection of improvements from dietary antioxidant intervention. Furthermore, the study
protocol sought to emphasise an upper body task in which arm flexion/extension was
repeated to exhaustion.
The main aim of the study was to assess whether supplementing with rooibos
polyphenols for a period of four weeks prior to a repeated arm flexion/extension fatiguing
exercise protocol (isokinetic controlled movement at 60 degrees per second) to
exhaustion could result in enhanced physical performance demonstrated by increased
strength expression in terms of force output (Nm) and total work done (joules). The
essential premise of this study was to investigate whether rooibos (when taken as a
supplement) acted as an ergogenic aid and could therefore be construed as a key dynamic
for improved exercise performance and by implication also have benefits for occupations
characterised by heavy physical work of a repetitive nature.
1.3 Hypotheses
In terms hypothesis testing a one-way analysis of variance was applied for each exercise
bout. The independent variable for the hypothesis testing relates to the trial (placebo
versus rooibos), whilst the dependant variable refers to the peak torque (Nm)
measurement or the total work (joules) done during five maximal bouts of elbow
extension and flexion exercise. This can be stated as follows:
• The null hypothesis (H0) is that there is no difference between the trials (placebo
versus rooibos) and equality between the means (peak torque or total work).
• The alternative hypothesis (H1) is that there is a difference between the means (peak
torque or total work) during the trials (placebo versus rooibos).
94 S.E.H. Davies et al.
1.4 Limitations of the study
Whilst study participants kept dietary records and were advised to avoid foods rich in
antioxidants it is recognised that this was very much dependant on the integrity of the
individual. This is acknowledged as a potential shortcoming of the study. The study
participants were also requested not to alter their levels of physical activity during the
study, and this may also be construed to be a limitation, as this was dependant on the
participants adhering to this request without any direct oversight.
2 Methodology
The sample included thirty-two adult male participants (mean age 22.2 years) who were
randomised in a single blinded, cross-over placebo controlled study. In order to
reasonably control the homogeneity of the sample group, only males were recruited for
this study to prevent any possible gender differences in exercise capacity under specific
conditions. All participants volunteered and signed an informed consent form. The
volunteers were healthy and had no contraindications for participation in the study as
determined by the physical activity readiness questionnaire (PAR-Q). The study
conforms to the principles of the Helsinki Accord and was approved by the Institutional’s
Faculty of Health and Wellness Sciences Research Ethics Committee (REC2011/H02).
The participants were required to ingest three standardised rooibos or placebo
capsules per day for four weeks prior to the exercise insult. The capsules contained a
fermented rooibos extract (standardised with a content of ~340 mg of total rooibos
polyphenols). The proposed dosage is equivalent to about six cups of rooibos herbal tea
per day and ought not to be perceived as a ‘megadose’ (Askew, 2002). This approach
took cognisance of concerns raised by a number of researchers who have suggested that
megadoses and long-term use of antioxidants can be harmful (Herbert, 1993; Cao and
Cutler, 1993). The rooibos dosage was premised on previous standardised protocols that
have been employed in exercise and oxidative stress research and other aligned studies
(Marnewick et al., 2011, 2016). The issue of a megadose is mentioned, because over
dosing could result in stomach upsets, cramps etc. and thus may have had the potential to
confound the purpose of the study.
The study participants were required to complete estimated dietary records for three
consecutive days (two week days and one weekend day) per week to ascertain their
compliance to the dietary restrictions during the study period. Considerable emphasis was
placed on all participants avoiding known anti-oxidant rich foods and beverages, along
with other substances e.g. alcohol that may have confounded the outcomes. Furthermore,
the participants were encouraged to continue with their normal daily/weekly routines in
terms of exercise and not to vary their exercise behaviour during the study. However it is
acknowledged that if participants did engage in additional exercise (or less) then this may
be a limitation of the study. The rooibos and placebo capsule intake during the study
period were monitored by counting the remaining capsules in the holder the participants
had to return in order to receive a new holder with the relevant capsules, i.e., rooibos or
placebo. The exercise tests were performed at the same time in the morning (whether the
participant was in the rooibos experimental arm, or in the placebo arm of the study) with
a standardised breakfast and water fluid intake.
The efficacy of rooibos Aspalathus linearis as an ergogenic aid 95
The exercise test employed involved isokinetic dynamometry, which has been
commonly used for the evaluation of muscle strength in sports and medicine. Isokinetic
dynamometry has been widely utilised because the technique evaluates the function as
well the strength of a joint (Harbo et al., 2012). An isokinetic muscle action is one where
the speed of movement remains constant irrespective of the magnitude of forces
generated by the participating muscles (Hislop and Perrin, 1967). According to Nitschke
(1992) an isokinetic dynamometer is an electromechanical device that can measure the
performance of an isokinetic muscle action in most major joints of the human body. The
parameters that can be obtained about an isokinetic muscle action from a dynamometer
include force (Newtons) torque (Newton-meters), range of movement (degrees), angular
velocity (degrees per second) and duration (seconds) of muscle action. Isokinetic
dynamometers are widely used in sport and exercise testing protocols, especially if the
study wishes to measure accurately the performance of a muscle and/or joint motion.
The exercise test protocol for this study entailed a maximal fatiguing elbow
flexion/extension exercise including 5 sets of 15 all-out voluntary contractions separated
by 10-second intervals on a Biodex System 3 at a speed of 60º per second. The
participant was placed in a seated position while the axis of rotation was through the
centre of the trochlea and the capitulum, bisecting the longitudinal axis of the shaft of the
humerus. The set-up and positioning of the participant including stabilising straps are
fully described in the p.3-37 and p.3-38 of the Biodex System 3 Pro Operation Manual.
The Biodex System 3 is recognised for its mechanical reliability and validity for exercise
testing (Drouin et al., 2004). Depending on which phase of the study the participant had
been randomly assigned (rooibos or placebo), the protocol was repeated with a change in
the supplementation regime.
Figure 1 Isokinetic elbow arm flexion/extension setup on Biodex (see online version for colours)
96 S.E.H. Davies et al.
3 Results
The results show the responses of participants during a randomised single blinded, cross-
over placebo controlled study. According to the dietary records, returned capsule holders
and interviews on the day of the exercise regimes, participants complied with the dietary
restrictions and capsule intake over the study period. Means and standard deviations were
calculated for the study participants for descriptive anthropometry (Table 1). A one-way
analysis of variance was used to examine the physical performance differences via
isokinetic dynamometry during the two experimental trials, namely placebo and rooibos
supplementation. The level of statistical significance was set at P ≤ 0.05. The data trends
during elbow extension across the five exercise bouts were similar in the placebo and
rooibos trial. While in contrast during elbow flexion the rooibos trial exhibited
consistently greater peak torque (Nm) and also more total work (joules) done across the
five exercise bouts. However the P values generated by applying one-way analysis of
variance for each trial (placebo versus rooibos) and for each exercise bout did not
demonstrate a significant difference, although the effect size during exercise bouts 3 and
4 for elbow flexion was of interest (see Table 2 and Figure 2).
This trend in terms of improved performance was also reflected during elbow flexion
for total work completed (placebo versus rooibos). Whilst the results, particularly during
elbow flexion, provide an indication of the possible ergogenic benefit of antioxidant
ingestion using rooibos, the outcomes were not as strong as those using the same
isokinetic protocol reported by Marnewick et al. (2016) when participants ingested an
acute dose of rooibos and performance outcomes were significantly higher in terms of the
total work (P = 0.019), as well as average power (P = 0.021), while average peak torque
was significantly greater (P = 0.01) during the elbow extension motion in the second (of
five) exercise bouts when comparing rooibos with placebo trials.
Table 1 Anthropometric characteristics of participants
Age (years) Mass (kg) Stature (cm) Body fat %
22.22 (4.27) 74.61 (13.50) 174.20 (7.17) 16.27 (3.21)
Note: Mean values with standard deviations in parentheses.
Table 2 Elbow extension and flexion: peak torque (Nm): mean values with standard deviations
in parentheses, P values and effect size
Peak torque extension Bout 1 Bout 2 Bout 3 Bout 4 Bout 5
Rooibos extension 32.3 (7.5) 30.8 (7.1) 31.6 (8.3) 30.2 (8.5) 32.0 (8.6)
Placebo extension 33.12 (8.2) 31.31 (7.5) 29.3 (6.1) 30.0 (5.8) 31.1 (7.6)
P= 0.68 0.79 0.21 0.50 0.68
Effect size 0.10 0.06 0.31 0.02 0.11
Peak torque flexion Bout 1 Bout 2 Bout 3 Bout 4 Bout 5
Rooibos flexion 48.3 (10.6) 41.8 (10.5) 39.0 (10.1) 36.3 (8.9) 36.9 (8.8)
Placebo flexion 45.4 (9.6) 38.9 (8.8) 35.2 (7.6) 32.9 (7.2) 34.7 (8.1)
P= 0.26 0.24 0.08 0.09 0.29
Effect size 0.2 0.29 0.42 0.42 0.26
The efficacy of rooibos Aspalathus linearis as an ergogenic aid 97
Figure 2 Elbow extension and flexion: peak torque (Nm) during five bouts of maximal exercise:
mean values and trends (see online version for colours)
Table 3 Elbow extension and flexion: total work (joules) during five bouts of maximal
exercise: mean values with standard deviations in parentheses, P values and effect size
Total work
extension Bout 1 Bout 2 Bout 3 Bout 4 Bout 5
Rooibos ext 470.0 (138.7) 431.3 (87.6) 413.3 (95.6) 394.6 (84.0) 406.0 (98.5)
Placebo ext 490.5 (161.0) 441.0 (105.8) 402.5 (73.9) 386.8 (65.9) 391.2 (85.8)
P= 0.58 0.69 0.61 0.67 0.52
Effect size 0.13 0.09 0.12 0.14 0.16
Total work
flexion Bout 1 Bout 2 Bout 3 Bout 4 Bout 5
Rooibos flex 749.9 (163.9) 606.8 (133.4) 537.1 (122.5) 500.8 (111.1) 505.6 (114.5)
Placebo flex 720.9 (154.9) 579.0 (121.2) 502.8 (106.7) 464.5 (98.5) 474.9 (109.3)
P= 0.47 0.38 0.23 0.17 0.27
Effect size 0.95 0.21 0.29 0.34 0.27
Figure 3 Elbow extension and flexion: total work (joules) during five bouts of maximal exercise:
mean values and trends (see online version for colours)
98 S.E.H. Davies et al.
The means and standard deviations, along with P values and effect size, are presented in
tabulated form, whilst the graphs show the data trends and the onset of fatigue during
each elbow extension or flexion exercise bout (1–5) in the placebo versus rooibos trails
for peak torque (Nm) and total work (joules) achieved (Table 2, Figure 2, Table 3 and
Figure 3).
4 Discussion
It is acknowledged that there is considerable controversy in the literature regarding the
impact of antioxidant supplementation on exercise performance. Draeger et al. (2014), in
his review of twelve studies (2006–2013) on the topic of antioxidant supplementation and
exercise, attributed the varied outcomes mainly because of differences in the
methodologies employed, which included differing vitamin dosages, study length, sample
size, differences in gender, age, and subjects characteristics (athletes and non-athletes).
These differences make it difficult to draw conclusions about the advantages and
disadvantages of antioxidant vitamin supplementation. This debate is further highlighted
in the present study that utilised a chronic (daily) supplementation regime over a four-
week period prior to testing, when compared to the study by Marnewick et al. (2016) that
used an acute dose of rooibos on the day of physical testing. In both studies [the present
one and Marnewick et al. (2016)] the same isokinetic exercise test protocol was used,
only the dosage regime was different. While the present study utilised a chronic dose of
rooibos elicited similar improvement trends in strength and work done when compared to
the acute dosage study, it was notable that the performance improvements were
significant (P ≤ 0.05.), with an acute dose of rooibos on the day of testing. In general
terms however, Clarkson and Thompson (2000) reported that trained athletes who ingest
antioxidant supplements show evidence of reduced oxidative stress and suggest further
research to fully document the efficacy and safety of long-term antioxidant supplement
use. This issue is apparent in terms of the present study, in which it appears the
bioactivity from the rooibos had beneficial effects on physical performance during
repeated bouts of exhaustive arm flexion exercise, however the precise mechanism of
action is not fully understood and therefore requires further research.
The results from this study show that rooibos antioxidant supplementation during
physical activity may have important considerations for ergonomic and human factors
practitioners. This was demonstrated notably by the improved performance during elbow
flexion in terms of peak torque (Nm) through all five bouts of exercise, which in turn was
complimented by higher levels of total work (joules) in all five flexion bouts of exercise.
This implies that rooibos may have a beneficial ergogenic effect on fatigue during
repetitive tasks. It is argued here that the potential benefits of antioxidant ingestion,
especially in tasks characterised by repetitive physical work, may provide further support
for Shearer et al.’s (2016) view that a better understanding of the nutritional status of the
worker has the potential to influence many work tasks. The value of antioxidant
supplementation is reiterated by Clarkson and Thompson (2000) who make the point that
no one questions the importance of ingesting a diet rich in antioxidants for all those
persons who exercise and train regularly. It is acknowledged that whilst a substantive
amount of research has focused on the biomechanical and physiological parameters of
workers (Salvendy, 2012), less attention, however has been given to nutritional issues. In
The efficacy of rooibos Aspalathus linearis as an ergogenic aid 99
particular the role of antioxidant supplementation has hitherto attracted little research in
the field of ergonomic and human factors. The findings from this present study show that
supplementing with rooibos over a period of four weeks, had positive outcomes (although
not statistically significant) in terms of physical performance notably during maximal
elbow flexion exercise. Thus, the results from this study that employed a chronic dosage
regime and the acute dosage regime by Marnewick et al. (2016), provide an indication
that supplementation with a known antioxidant-rich beverage such as rooibos Aspalathus
linearis may have ergogenic benefits for those persons who participate in competitive
sport and perform repeated bouts of high intensity exercise and for those persons
habitually engaged in repetitive and physically fatiguing work tasks.
5 Conclusions
This study indicated that individuals who ingested the standardised rooibos Aspalathus
linearis for a four-week period prior to a repetitive fatiguing exercise protocol generated
consistently higher muscular force output in terms of peak torque (Nm) during elbow
flexion in all five bouts of maximal exercise, as well as exhibiting an increased total work
(joules) during all five elbow flexion exercise bouts. These outcomes may have important
implications in the field of exercise science, especially in terms of training where
repetitions and sets of exercise are utilised in structured loading of volumes and
intensities of work. It is apparent from the findings in this study and those presented by
Marnewick et al. (2016) that athletes who have the option to supplement with the
antioxidant rooibos may experience an ergogenic effect and improved performance
outputs during repetitive bouts of training. This may allow coaches and/or athletes to plan
their diet and training more effectively, with a view to improving competition
performance as well. In terms of the workplace, where tasks are often highly repetitive
and fatiguing the findings from this study reinforce the need for a better understanding of
antioxidant supplementation for workers, engaged in physically arduous tasks.
It is tentatively suggested that a worker/person engaged in tasks of a repetitive nature
requiring forceful actions may benefit from supplementing his/her diet with rooibos
Aspalathus linearis, a recognised antioxidant, because it may reduce the precursors to
cellular oxidative damage, namely ROS and RNS. Furthermore, research by Marnewick
et al. (2016) suggests that an acute dose rooibos prior to exercise may have a more
beneficial ergogenic effect than a chronic dose as reported in this study. It is a
recommendation that further research is conducted to establish the efficacy of rooibos as
an effective antioxidant and ergogenic supplement for enhancing exercise or work
performance for those persons engaged in repetitive physical tasks.
Acknowledgements
The authors wish to acknowledge the funding support provided by the South African
Rooibos Council for this study.
100 S.E.H. Davies et al.
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