Strength and Conditioning for Adolescent Endurance Runners

Full text

Strength and Conditioning for Adolescent Endurance Runners

Strength and Conditioning for Adolescent Endurance Runners
ABSTRACT
For the adolescent athlete who chooses to specialize in endurance running, strength and conditioning
(S&C) activities provide a means of enhancing several important determinants of performance and may
reduce the risk of overuse injury. It is recommended that adolescent endurance runners include at least
two S&C sessions per week that comprise of movement skills training, plyometric and sprint training,
resistance training, plus exercises designed to target specific tissues that are vulnerable to injury. This
article describes how these modalities of training can be integrated into the routine of adolescent
endurance runners.
Key words: paediatric, endurance, distance running, youth, concurrent training
INTRODUCTION
Endurance running is a popular choice of sport for young athletes. For example, in 2016-17, cross-
country was the fourth and fifth largest sport by participation for boys and girls respectively in USA
high schools (see www.nfhs.org/ParticipationStatistics), and endurance running represented the second
most popular sport (18.7%) in a survey (n=7794) of Scandanvian 14 year olds (83). A young athlete
should be exposed to a wide range of sports and physical activities during their adolescence, however
the priority should be placed on the development of rudimentary motor skills and muscular strength
(49). Endurance training during early-adolescence (11-14 years old) should form part of an active
healthy lifestyle but should not take precedence over other modalities of sport-training (80). Endurance
sports are typically associated with a high volume of training (80), which places the developing body
of a young athlete under a high level of stress that could leave them susceptible to overtraining
syndrome, illness and overuse injury (54). Therefore, specialization in endurance running should not
occur until late-adolesence, when a young athlete’s body is sufficiently mature and well-conditioned to
cope with the rigours of this type of training. Strength and conditioning (S&C) activities might
contribute towards lowering the risk of injury in athletes (45, 82), therefore providing sport-specific
recommendations for this vulnerable population is important.
Endurance running is primarily limited by cardiovascular and metabolic factors, however there is an
abundance of research showing that strength training (ST) activities (resistance training (RT), explosive
resistance training (ERT) and plyometric training (PT)) can provide performance benefits to middle-
(0.8-3 km) and long-distance (>3 km) runners (16, 29). A plethora of literature also exists that

demonstrates ST activities are also a safe and effective way of enhancing proxy measures of athletic
performance in adolescents of both sexes (10, 41, 46). Specifically, compared to sport-only training,
various forms of ST augment improvements in maximal strength, explosive strength, muscular
endurance, sprint speed, agility test time, tennis serve velocity, kicking velocity, throwing velocity, and
general motor skills (10, 40, 41, 46). However, there are currently no papers which have specifically
summarized the effect of ST modalities on aerobic-related qualities in young athletes. For practitioners
working with young distance runners in particular, it would be useful to establish whether ST activities
offer any benefit to performance-related factors and how such training techniques could be applied in
practice. Therefore, the aims of this article are to briefly review the literature that has investigated the
efficacy of ST on the determinants of endurance running in adolescent runners, and provide guidelines
for best practice to improve performance and minimize the ocurrence of overuse injury.
Figure 1. Primary determinants of endurance running performance and the modalities of training to
improve each. V
̇O2max = maximal oxygen uptake, sV
̇O2max = speed at maximal oxygen uptake.
DETERMINANTS OF ENDURANCE RUNNING PERFORMANCE
Endurance running performance is determined by several key physiological variables, which are
summarized in figure 1. The physiological determinants of performance for adolescents appears to be
similar to those of adult runners (3, 27). A number of investigations have confirmed that maximal

oxygen uptake (V
̇O2max) is a significant predictor (r=0.5-0.9) of performance for 1.5 km (1, 3), 3 km (1,
50, 87), 5 km (1, 27) and cross-country (24, 34) in young (10-18 years) groups of runners. The
proportion of V
̇O2max that can be sustained for a given duration (known as ‘fractional utilization’), has
also been shown to significantly correlate with endurance running performance in adolescents (50, 87).
Running economy (RE), defined as the metabolic cost of running a given distance (79), is related to
middle- (3, 87) and long-distance running performance (24, 34), and importantly, is influenced by
neuromuscular related qualities, which can potentially be improved with ST activities (16, 29).
Additionally, speed at V
̇O2max, which is a product of V
̇O2max and RE, correlates well with distance
running performance in adolescents (1, 3, 24, 27).
The contribution of anaerobic factors to endurance running performance in adults is well-established
(20), however the influence of anaerobic determinants on performance in young endurance runners has
not been fully delineated. This is likely due to the unspecific nature of the tests (Wingate test, isokinetic
strength tests, counter-movement jump height) utilized to quantify anaerobic and neuromuscular
capacities in studies that have investigated young distance runners (3, 24, 28). Anaerobic capacity and
neuromuscular capabilities are thought to play a large role in discriminating performance in runners
who are closely matched from an aerobic perspective (22, 67). Mahon and co-authors (50) also showed
that 55 m sprint and counter-movement jump were significant predictors of 3 km time trial in
preadolescent children, although given the age of the participants, this finding could simply be a
reflection of individuals possessing high or low levels of athletic ability across the range of the tests
utilized. Speed at V
̇O2max probably provides the most sport-specific representation of neuromuscular
capabilities in distance runners, however measures of maximal running speed and anaerobic capacity
are also important attributes (65). For an 800 m specialist in particular, near-maximal velocities of
running are reached during the first 200 m of the race (74), which necessitates a high capacity of the
neuromuscular and anaerobic system. Similarly, the quickest finisher at the end of a middle- or long-
distance race often determines the winner (85), thus possessing a higher top speed is potentially crucial
for achieving success in distance running. Regardless of the capacity for anaerobic and neuromuscular
factors to predict endurance performance in adolescents, activities to develop sprint speed and muscular
strength-qualities as part of a well-rounded physical training programme is recommended during
adolescence irrespective of whether sport-specialization has occurred (47, 49).
EFFECT OF STRENGTH TRAINING ON AEROBIC-RELATED PARAMETERS
Based upon the findings of recent reviews (16, 29), it is suggested that supplementing the training of an
endurance runner with ST is likely to provide improvements in RE, time-trial (1.5 km – 10 km)
performance and anaerobic parameters such as maximal sprint speed. Improvements in RE in the
absence of changes in V
̇O2max, speed at V
̇O2max, blood lactate and body composition parameters suggests

that the underlying mechanisms predominantly relate to alterations in intra-muscular co-ordination and
increases in stiffness (16). Specifically, ST brings about increases in motor unit recruitment, firing
frequency and musculotendinous stiffness, which are thought to optimize the length-tension and force-
velocity relationships of active skeletal muscle, thus reducing the metabolic cost of running (36). It is
clear that the inclusion of ST also does not adversely affect V
̇O2max, blood lactate markers or body
composition (16). Concurrently, RE showed improvements of 2-8% with ST compared to a running-
only control group following a 6-14 week intervention that includes 2-3 ST sessions per week (16).
Efficacy in Adolescent Runners
Three studies have investigated the effect of ST specifically in young (<18 years) middle- or long-
distance runners and these are summarized in table 1. A recent study by Blagrove et al. (17) found that
two weekly sessions of ST (mainly PT and RT) added to the programme of post-pubertal adolescent
distance runners (17 years) for ten weeks was ‘possibly beneficial’ for RE (effect size: 0.31-0.51) and
‘highly likley beneficial’ for maximal sprint speed. However, only the maximal speed improvement
reached statistical significance (p<0.05) compared to the change observed in the control group. Mikkola
et al. (58) took a group of trained male and female distance runners (mean: 17 years, V
̇O2max: 62.5
mL.kg-1.min-1) and following eight weeks of ERT, PT and sprint training, noted a difference (-2.7%) in
RE at 14 km.h-1 and improvements in anaerobic capabilities (speed during the maximal anaerobic
running test and 30 m sprint) compared to a running-only group. It is noteworthy that both of these
investigations (17, 58) included sprints (3-10 x 30-150 m) as part of the intervention, which provides a
highly specific overload to the neuromuscular system in endurance runners. Interestingly, participants
in the ST intervention groups in these studies reduced their weekly running volume to accommodate
the additional S&C activities. Total time spent training was however very similar between intervention
and control groups.
Bluett and associates (18) found that ten weeks of concurrent aerobic and ST provided little strength
advantage and no change in 3 km time trial performance in 10-13 year old competitive runners
compared to running only. This study utilized mainly single joint machine-based RT and did not
measure any physiological parameters, which may explain the lack of effect observed. The authors
speculated that excessive fatigue resulting from the concurrent training regimen may have compromised
both strength and endurance adaptations (18). Interestingly, the blunting of strength adaptation which
is often observed in adult performers when both strength- and endurance-training are included in the
same training session (90) appears not to occur in children (53) and adolescents (75, 76). As the
interference phenomeon is mediated by training volume and recovery from sessions (5), it seems likely
that the volumes of each training modality included in the aforementioned studies were insufficient to
negatively impact upon strength-related adaptation. Indeed, in elite youth soccer players (17 years) who

utilize higher workloads compared to younger performers, larger improvements were evident in
strength and sprint performance after five weeks when ST was performed after sport-specific endurance
training on two days per week, compared to a group who adopted a ST followed by endurance training
sequence (33).

Authors
Participants
n (I/C), sex, age
Study
duration
Running volume
ST
frequency
ST prescription
Main strength
outcomes
Main running-related
outcomes
Blagrove
et al. (18)
18 (9/9), both,
17.2 years
10
I: 151 min.wk-1
C: 213 min.wk-1
2 per
week
PT (3-4 x 6-8/15 m): box
jumps, A-skips, hurdle
jumps
RT (2-3 x 6-8 reps): back
squat, RDL, rack pull,
deadlift, step-ups, leg
press, calf raise
MVC (15.4%,
ES=0.86, p<0.05),
vGRFjump (6.1%,
ES=0.93)
CMJ, little
difference
compared to C
RE@ sLTP (3.2%,
ES=0.31), sLTP -1 km.h-1
(3.7%, ES=0.47), sLTP -2
km.h-1 (3.6%, ES=0.51)
20 m sprint (3.6%, ES=0.32,
p<0.05)
Bluett et
al (19)
12 (6/6), both,
10-13 years
10
Both groups: 2 x
runs per week
(1x25-30 min
continuous,
1xintervals)
2 per
week
RT (3-4 sets x 10-12
reps): leg curl, leg
extension, leg press,
upper limb/trunk
exercises
Increase (12.2-
24%) loads lifted
during ST but no
change in peak
torque pre-post I
3 km TT no change in either
group
Mikkola
et al (59)
25 (13/12), both,
17.3 years
8
I: 8.8 h.wk-1
(19% running
replaced with
ST),
C: 8.5 h.wk-1
3 per
week
PT: alternative jumps, calf
jumps, squat jumps,
hurdle jumps
ERT (2-3 x 6-10 reps):
half-squats, knee
extension, knee flexion,
leg press, calf raise
MVC (8%), 1RM
(4%), RFD (31%)
on leg press; all
p<0.05.
CMJ and 5-bounds
little difference
compared to C
RE@14 km.h-1 (2.7%,
ES=0.32, p<0.05),
@10,12,13 km.h-1, NS
BL@12 km.h-1 (12%,
p<0.05), @14 km.h-1 (11%,
p<0.05)
sMART (3.0%, p<0.01), s30
m sprint (1.1%, p<0.01)
C=control, I=intervention, ST=strength training, wk=week, PT=plyometric training, RT=resistance training, RDL=Romanian deadlift, MVC=maximum
voluntary contraction, ES=effect size, vGRFjump=vertical ground reaction force during squat jump, CMJ=counter-movement jump, RE=running economy,
sLTP=speed at lactate turnpoint, TT=time trial, ERT=explosive resistance training, 1RM=one repetition maximum, RFD=rate of force development, NS=not
statistically significant, BL=blood lactate
Table 1. Summary of studies (n=3) that have investigated the effects of a strength training intervention on adolescent endurance runners.

Research investigating the impact of ST techniques on performance-related measures in young athletes
has tended to use participants from field-based sports, martial arts, court sports, aquatic sports,
gymnastics and strength-based sports (40, 46). A number of studies using adolescent participants from
other sports that require high-levels of aerobic fitness have observed superior improvements in Yo-Yo
test (44, 51, 72, 91) and middle-distance time-trial performance (70, 73) after various modalities of ST
were added (6-12 weeks) to a sports-specific training programme, compared to only practicing the sport.
Taken together, it appears that the addition of 2-3 ST sessions to the weekly routine of adolescent
endurance runners provides a small but potentially meaningful benefit to RE and maximal sprint speed
following an 8-10 week intervention. Evidence for improvements in performance exists for adult
runners (16), however there is currently a lack of research in younger endurance runners. Benefits are
likely to be larger for interventions of a longer duration (29) and for ST programmes that are supervised
by qualified practitioners (16). Although the majority of studies in adults supplement a runners training
with ST, there also appears to be no disadvantage to reducing weekly running volume to accommodate
the addition of two weekly ST sessions.
PRACTICAL RECOMMENDATIONS
Timing of Specialization and Long-Term Athlete Development
Adolescence represents an important period of development in young athletes where significant
alterations in hormonal status causes rapid physical growth (52). Contemporary views of long-term
youth development suggest adolescents should avoid training routines that focus on intensive training
in a single sport (for >8 months per year), or a total weekly training volume (in hours) that exceeds the
athletes age in years, until late-adolescence (47, 49, 63). Evidence from several endurance sports shows
elite senior athletes tend to specialize at a later age, and participate in a diverse range of sports during
their earlier years (26, 60). Recent work has also shown that very few middle-distance runners ranked
in the UK top 20 in the under-13 and under-15 age-groups experience success as senior runners (43).
Young athletes who adopt an early-diversification, late-specialization approach to their development
have fewer injuries, are at less risk of overtraining, and play sports longer than those who specialize in
one sport before puberty (21, 30).
The youth athlete development model suggests a wide range of physical activities and training
modalities should be utilized during adolescence, however movement skills training (MST) and
development of strength qualities should be prioritized (47, 49). The emphasis on ST activities
throughout an athletes development is thought to maximize adaptations to inter- and intra-muscular
coordination, during a period when neuroplasticity is high (64). Improvements in muscular strength and
motor control during this period have also been shown to improve physical performance (10, 46) and

lower the risk of sustaining an injury (62, 82). It is recommended that endurance training (and metabolic
conditioning) is not emphasised, relative to other biomotor abilities, until late-adolescence (49), as
typically this type of training is associated with high volumes of work, which may lead to injury or
overtraining (54). Moreover, pre-pubertal children have tended to show smaller changes (<10%) in
aerobic measures following endurance training interventions compared to post-pubertal adolescents and
adults (54, 56). A recent study also showed that pre-pubertal boys (11 years) were metabolically
comparable to well-trained endurance athletes and experienced less fatigue during high-intensity
exercise compared to untrained adults (14). It was suggested that pre-pubertal children avoid specific
training to develop aerobic metabolic qualities and shift priority during post-pubertal years once
movement technique and mechanical competency have been developed (14). Due to the risks associated
with early-specialization, it is recommended that adolescent athletes younger than 15 years old do not
solely specialize in endurance running, but should participate in a wide range of sports and physical
activities, including ST.
Organization of the Training Microcycle
Prior to specialization in a sport of a young athletes choice, physical training should be semi-structured
and not emphasize peaking for competitions (26, 63). Conversely, an adolescent endurance runner will
typically run 45 to 55 miles weekly in preparation for a race (80), which when combined with academic
and social commitments, can place a high level of physical and psychological stress on a young athlete
(54). This necessitates a well-organized approach to training that caters to the needs of individual
athletes and ensures sufficient periods of recovery between bouts of training.
Two seven-day microcycle designs are shown in Table 2a and 2b to illustrate how an adolescent
endurance runner could incorporate S&C activities into their routine. Adolescent distance runners
typically perform 2-3 high-intensity running sessions per week (15), and these should form the priority
sessions in the programme (Table 2a and 2b; Tuesday, Thursday and Saturday). Similarly, a minimum
of two ST sessions per week are suggested for adolescents (11, 48) and endurance runners (16). RT
sessions should ideally take place at least three hours after a running session (6) and at least 24 hours
recovery should follow after ST before an intensive running session (31). A novel approach to
organizing S&C activities around training and lifestyle commitments with young runners is to
incorporate shorter periods of activity (‘training units’) as part of running sessions wherever possible
(see Table 2b). This type of programming is useful for young runners who perhaps cannot access a
specialist S&C facility, and therefore perform a largely home-based routine, or are unable to commit to
two full S&C sessions per week. Each training unit takes 10-20 min to complete, thus making it easy to
integrate some purposeful S&C prior to or after running sessions. It is important to note that studies in

adolescent distance runners (17, 58) have shown that including weekly ST sessions are more effective
than increasing running volume, at least in the short-term (8-10 weeks).
Assuming runners are of a non-strength trained status, it appears that a variety of ST modalities can be
used to achieve similar outcomes. However to maximize long-term adaptations in young athletes, it is
suggested that a periodized approach is adopted with fundamental skills training and RT prioritized
initially (9, 25, 47). Figure 2 provides an overview of the session design and characteristics of specific
training units recommended for adolescent distance runners. A similar session design framework has
also been employed successfully in other investigations that used distance runners embarking upon a
ST programme for the first time (9, 17, 58).
Figure 2. Recommended structure of a strength and conditioning session for adolescent endurance
runners. Characteristics and example exercise prescription for individual training units are also shown.
Prescription is sets x repetitions (unless stated).

Day
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Session
(am) Easy 30 min
run
(pm) S&C session
Interval training
session
(am) Cycle or
swim 30 min
(pm) S&C session
Tempo run* (20-
30 min)
Rest
Race or interval
training session
Easy 45 min run
S&C = strength and conditioning. * Continuous fast run performed at approximately 10 km race-pace (speed at lactate turn-point)
Table 2a. Example of a seven day microcycle for an adolescent endurance runner.
Day
Mon
Tues
Wed
Thurs
Fri
Sat
Sun
Session
Easy 30 min run +
PT and RT
MST + Interval
training session
Cycle or swim 30
min + RT and SC
PT + Tempo run
(20-30 min)
Rest
Race or interval
training session +
SC
Easy 45 min run +
MST
PT = plyometric training, RT = resistance training, MST = movement skills training, SC = specific conditioning
Table 2b. Example of a seven day microcycle for an adolescent endurance runner with strength and conditioning activities organised as training units before
or after running sessions. Training units should last 10-20 min with the focus on movement quality rather than inducing high levels of fatigue.

Movement Skills Training
The inclusion of MST in the routine of adolescent distance runners is recommended, and is likely to
reduce long-term injury risk (45, 62, 82). This form of conditioning is ideal to include as part of a
movement preparation warm-up routine prior to running and ST sessions, or as an independent training
unit (82). MST should include activities to enhance both general (fundamental) and specific (running-
related) movement skill and control, balance and dynamic stability, and low-level resistance training
targeting specific muscle groups, such as the gluteals (37).
Plyometrics and Sprint Training
Low intensity plyometric-based exercise that aim to develop ankle stiffness, such as skipping, low-box
re-bound jumps, mini hurdle jumps and short range hopping tasks, offer a potent stimulus to the
neuromuscular system and have independently been shown to enhance RE and time trial performance
(12, 68, 71, 81, 86). It is suggested that 30-60 foot contacts per session are utilized initially with
adolescent distance runners (17). Sprint training has also been used in several investigations showing
enhancements in maximal speed and performance-related factors (17, 58, 59, 66). Three to five sets of
short distance (30-60 m) technical and maximal sprints performed 2-3 times per week is likely to provide
benefits to adolescent endurance runners.
Resistance Training
Resistance training, which should include both ERT and heavy RT, increases motor unit recruitment
and firing frequency, thus enhances a runners ability to appropriately control and express force during
ground contact. Although changes in fat-free mass appear to be minimal following a ST intervention in
distance runners (16), a targeted RT programme, that aims to increase muscle mass specifically around
the proximal region of the lower limb may enhance biomechanical and physiological factors, which
positively influence RE (36). Exercises, such as squats, deadlifts, step-ups and lunge patterns, which
possess similar kinematic characteristics to running gait, are likely to provide the greatest transfer (8)
and have been utilized in several previous investigations (9, 17, 58). Loaded jump squats, medicine ball
throwing and weightlifting are examples of suitable ERT activities that can also be utilized (8, 9, 59).
Upper limb exercises such as press-ups, rowing exercises and overhead presses, should also be
incorporated to offset the vertical angular momentum created by the lower limbs and aid in controlling
excessive rotation forces (42, 69, 77). One to three sets of each exercise performed in a moderate
repetition range (8-12 repetitions) is likely to provide non-strength trained individuals with a stimulus
sufficient to drive neuromuscular adaptation whilst developing skill in each exercise (9, 17, 59). Higher
loads (≥80% one repetition maximum) and lower repetition ranges (3-8 repetitions) are likely to be

required to provide further overload in strength-trained adolescents, with volume of work moderated
via an increase in sets.
Specific Conditioning
Many young endurance runners are motivated to include S&C activities to reduce injury risk more so
than improve their performance (15). Youth endurance athletes have been identified as a high-risk group
due to the rigorous training that they undertake during a critical period of their physical and emotional
development (54, 80). Indeed, injury incidence rate has been reported to be higher in adolescent elite
endurance runners compared to other endurance sports (88). Moreover, female adolescent runners tend
to display higher rates of low bone mineral density and bone stress injuries compared to young female
athletes in other sports (78). Overuse injuries occur over multiple running sessions when structure
specific cumulative load exceeds capacity (13). MST, PT and resistance-based exercises are likely to
contribute towards lowering risk of injury via enhancements in motor control and increased bone
mineral density and tissue resilience (45, 62, 89). Exercises designed to expose specific muscles or
tissues to a high magnitude of load are also likely to provide benefits to tendon stiffness (35) and
tolerance to repetitive stress (7, 19, 61, 84, 89). It is recommended that such exercises are positioned in
final part of a session or performed separately, as pre-fatiguing muscles in isolation is likely to be
detrimental to performance in multi-joint tasks (4). Specifically for distance runners, targeted
conditioning exercises should focus on the specific structures which are vulnerable to injury, or the
muscles that contribute towards controlling the positioning of joints within the lower limb, such as: the
intrinsic joints of the feet, the calf-Achilles complex, gluteal and hamstring muscles (2, 32, 38, 55, 57,
61). In addition, specific exercises that target proximal musculature around the lumbopelvic-hip
complex (‘core stability’) are likely to offset the risk of several types of common overuse injuries in
runners (23). Specifically, exercises which facilitate greater strength and control of the hip abductors
and external rotators are likely to provide benefits (23, 39).
CONCLUSION
Endurance running performance is constrained by several important physiological variables, however
anaerobic and neuromuscular factors have also been recognized as being important. For the young
athlete, participating in a broad range of sporting and physical pursuits is recommended during early-
adolescence. Age-appropriate S&C should form an integral part of a well-rounded approach to the long-
term physical development of all young sports performers. Participating in endurance running events
can certainly form part of a programme of activities during adolescence, however it is suggested young
athletes should not solely specialize in endurance running until late-adolescence. For the young

endurance runner, adding ST sessions twice per week that includes RT, PT and sprinting, is likely to
provide benefits to RE and maximal sprint speed that translate to improved performance. Moreover,
these activities, plus MST and specific strengthening of tissues vulnerable to injury, are important for
lowering the risk of overuse injury.

REFERENCES
1. Abe D, Yanagawa K, Yamanobe K, and Tamura K. Assessment of middle-distance running
performance in sub-elite young runners using energy cost of running. Eur J Appl Physiol
Occup Physiol 77: 320-325, 1998.
2. Aderem J, and Louw QA. Biomechanical risk factors associated with iliotibial band syndrome
in runners: a systematic review. BMC Musculoskelet Disord 16: 356, 2015.
3. Almarwaey OA, Jones AM, and Tolfrey K. Physiological correlates with endurance running
performance in trained adolescents. Med Sci Sports Exerc 35: 480-487, 2003.
4. Augustsson J, ThomeÉ R, HÖrnstedt P, Lindblom J, Karlsson J, and Grimby G. Effect of pre-
exhaustion exercise on lower-extremity muscle activation during a leg press exercise. J
Strength Cond Res 17: 411-416, 2003.
5. Baar K. Training for endurance and strength: lessons from cell signaling. Med Sci Sports
Exerc 38: 1939-1944, 2006.
6. Baar K. Using molecular biology to maximize concurrent training. Sports Med 44 Suppl 2:
S117-125, 2014.
7. Baar K. Minimizing injury and maximizing return to play: lessons from engineered ligaments.
Sports Med 47: 5-11, 2017.
8. Bazyler CD, Abbott HA, Bellon CR, Taber CB, and Stone MH. Strength training for
endurance athletes: Theory to practice. Strength Cond J 37: 1-12, 2015.
9. Beattie K, Carson BP, Lyons M, Rossiter A, and Kenny IC. The effect of strength training on
performance indicators in distance runners. J Strength Cond Res 31: 9-23, 2017.
10. Behringer M, Heede Av, Matthews M, and Mester J. Effects of strength training on motor
performance skills in children and adolescents: a meta-analysis. Pediatr Exerc Sci 23: 186-
206, 2011.
11. Bergeron MF, Mountjoy M, Armstrong N, Chia M, Côté J, Emery CA, Faigenbaum A, Hall
G, Kriemler S, and Léglise M. International Olympic Committee consensus statement on
youth athletic development. Br J Sports Med 49: 843-851, 2015.
12. Berryman N, Maurel DB, and Bosquet L. Effect of plyometric vs. dynamic weight training on
the energy cost of running. J Strength Cond Res 24: 1818-1825, 2010.
13. Bertelsen M, Hulme A, Petersen J, Brund RK, Sørensen H, Finch C, Parner ET, and Nielsen
R. A framework for the etiology of running‐related injuries. Scand J Med Sci Sports 27: 1170-
1180, 2017.
14. Birat A, Bourdier P, Piponnier E, Blazevich AJ, Maciejewski H, Duche P, and Ratel S.
Metabolic and fatigue profiles are comparable between prepubertal children and well-trained
adult endurance athletes. Front Physiol 9: 387, 2018.
15. Blagrove RC, Brown N, Howatson G, and Hayes PR. Strength and conditioning habits of
competitive distance runners. J Strength Cond Res, 2017. [e-pub ahead of print]
16. Blagrove RC, Howatson G, and Hayes PR. Effects of strength training on the physiological
determinants of middle-and long-distance running performance: a systematic review. Sports
Med 48: 1117-1149, 2018.
17. Blagrove RC, Howe LP, Cushion EJ, Spence A, Howatson G, Pedlar CR, and Hayes PR.
Effects of strength training on postpubertal adolescent distance runners. Med Sci Sports Exerc,
2018. [e-pub ahead of print]
18. Bluett KA, De Ste Croix MB, and Lloyd RS. A preliminary investigation into concurrent
aerobic and resistance training in youth runners. Isokinet Exerc Sci 23: 77-85, 2015.
19. Bohm S, Mersmann F, and Arampatzis A. Human tendon adaptation in response to
mechanical loading: a systematic review and meta-analysis of exercise intervention studies on
healthy adults. Sports Med Open 1: 7, 2015.
20. Brandon LJ. Physiological factors associated with middle distance running performance.
Sports Med 19: 268-277, 1995.
21. Brenner JS. Sports specialization and intensive training in young athletes. Pediatr 138:
e20162148, 2016.

22. Bulbulian R, Wilcox AR, and Darabos BL. Anaerobic contribution to distance running
performance of trained cross-country athletes. Med Sci Sports Exerc 18: 107-113, 1986.
23. Chuter VH, and de Jonge XAJ. Proximal and distal contributions to lower extremity injury: a
review of the literature. Gait Posture 36: 7-15, 2012.
24. Cole AS, Woodruff ME, Horn MP, and Mahon AD. Strength, power, and aerobic exercise
correlates of 5-km cross-country running performance in adolescent runners. Pediatr Exerc
Sci 18: 374-384, 2006.
25. Cormie P, McGuigan MR, and Newton RU. Influence of strength on magnitude and
mechanisms of adaptation to power training. Med Sci Sports Exerc 42: 1566-1581, 2010.
26. Côté J, Lidor R, and Hackfort D. ISSP position stand: To sample or to specialize? Seven
postulates about youth sport activities that lead to continued participation and elite
performance. Int J Sport Exerc Psychol 7: 7-17, 2009.
27. Cunningham LN. Relationship of running economy, ventilatory threshold, and maximal
oxygen consumption to running performance in high school females. Res Q Exerc Sport 61:
369-374, 1990.
28. Dellagrana RA, Guglielmo LG, Santos BV, Hernandez SG, da Silva SG, and de Campos W.
Physiological, anthropometric, strength, and muscle power characteristics correlates with
running performance in young runners. J Strength Cond Res 29: 1584-1591, 2015.
29. Denadai BS, de Aguiar RA, de Lima LC, Greco CC, and Caputo F. Explosive training and
heavy weight training are effective for improving running economy in endurance athletes: A
systematic review and meta-analysis. Sports Med 47: 545-554, 2017.
30. DiFiori JP, Benjamin HJ, Brenner JS, Gregory A, Jayanthi N, Landry GL, and Luke A.
Overuse injuries and burnout in youth sports: a position statement from the American Medical
Society for Sports Medicine. Br J Sports Med 48: 287-288, 2014.
31. Doma K, Deakin GB, and Bentley DJ. Implications of impaired endurance performance
following single bouts of resistance training: an alternate concurrent training perspective.
Sports Med 47: 2187–2200, 2017.
32. Duffey MJ, Martin DF, Cannon DW, Craven T, and Messier SP. Etiologic factors associated
with anterior knee pain in distance runners. Med Sci Sports Exerc 32: 1825-1832, 2000.
33. Enright K, Morton J, Iga J, and Drust B. The effect of concurrent training organisation in
youth elite soccer players. Eur J Appl Physiol 115: 2367-2381, 2015.
34. Fernhall B, Kohrt W, Burkett LN, and Walters S. Relationship between the lactate threshold
and cross-country run performance in high school male and female runners. Pediatr Exerc Sci
8: 37-47, 1996.
35. Fletcher JR, Esau SP, and MacIntosh BR. Changes in tendon stiffness and running economy
in highly trained distance runners. Eur J Appl Physiol 110: 1037-1046, 2010.
36. Fletcher JR, and MacIntosh BR. Running economy from a muscle energetics perspective.
Front Physiol 8: 433, 2017.
37. Fort-Vanmeerhaeghe A, Romero-Rodriguez D, Lloyd RS, Kushner A, and Myer GD.
Integrative neuromuscular training in youth athletes. Part II: Strategies to prevent injuries and
improve performance. Strength Cond J 38: 9-27, 2016.
38. Franettovich MS, Honeywill C, Wyndow N, Crossley KM, and Creaby MW. Neuromotor
control of gluteal muscles in runners with achilles tendinopathy. Med Sci Sports Exerc 46:
594-599, 2014.
39. Fredericson M, Cookingham CL, Chaudhari AM, Dowdell BC, Oestreicher N, and Sahrmann
SA. Hip abductor weakness in distance runners with iliotibial band syndrome. Clin J Sport
Med 10: 169-175, 2000.
40. Granacher U, Lesinski M, Büsch D, Muehlbauer T, Prieske O, Puta C, Gollhofer A, and
Behm DG. Effects of resistance training in youth athletes on muscular fitness and athletic
performance: a conceptual model for long-term athlete development. Front Physiol 7: 164,
2016.
41. Harries SK, Lubans DR, and Callister R. Resistance training to improve power and sports
performance in adolescent athletes: A systematic review and meta-analysis. J Sci Med Sport
15: 532-540, 2012.

42. Johnston RE, Quinn TJ, Kertzer R, and Vroman NB. Strength training in female distance
runners: impact on running economy. J Strength Cond Res 11: 224-229, 1997.
43. Kearney PE, and Hayes PR. Excelling at youth level in competitive track and field athletics is
not a prerequisite for later success. J Sports Sci, 2018. [e-pub ahead of print]
44. Klusemann MJ, Pyne DB, Fay TS, and Drinkwater EJ. Online video–based resistance training
improves the physical capacity of junior basketball athletes. J Strength Cond Res 26: 2677-
2684, 2012.
45. Lauersen JB, Bertelsen DM, and Andersen LB. The effectiveness of exercise interventions to
prevent sports injuries: a systematic review and meta-analysis of randomised controlled trials.
Br J Sports Med 48: 871-877, 2014.
46. Lesinski M, Prieske O, and Granacher U. Effects and dose–response relationships of
resistance training on physical performance in youth athletes: a systematic review and meta-
analysis. Br J Sports Med 50: 781-795, 2016.
47. Lloyd RS, Cronin JB, Faigenbaum AD, Haff GG, Howard R, Kraemer WJ, Micheli LJ, Myer
GD, and Oliver JL. National Strength and Conditioning Association position statement on
long-term athletic development. J Strength Cond Res 30: 1491-1509, 2016.
48. Lloyd RS, Faigenbaum AD, Stone MH, Oliver JL, Jeffreys I, Moody JA, Brewer C, Pierce
KC, McCambridge TM, and Howard R. Position statement on youth resistance training: the
2014 International Consensus. Br J Sports Med 48: 498-505, 2014.
49. Lloyd RS, and Oliver JL. The youth physical development model: A new approach to long-
term athletic development. Strength Cond J 34: 61-72, 2012.
50. Mahon A, Del Corral P, Howe C, Duncan G, and Ray M. Physiological correlates of 3-
kilometer running performance in male children. Int J Sports Med 17: 580-584, 1996.
51. Makhlouf I, Castagna C, Manzi V, Laurencelle L, Behm DG, and Chaouachi A. Effect of
sequencing strength and endurance training in young male soccer players. J Strength Cond
Res 30: 841-850, 2016.
52. Malina RM. Physical growth and biological maturation of young athletes. Exerc Sport Sci Rev
22: 280-284, 1994.
53. Marta C, Marinho D, Barbosa T, Izquierdo M, and Marques M. Effects of concurrent training
on explosive strength and VO2max in prepubescent children. Int J Sports Med 34: 888-896,
2013.
54. Matos N, and Winsley RJ. Trainability of young athletes and overtraining. J Sports Sci Med 6:
353, 2007.
55. McKeon PO, and Fourchet F. Freeing the foot: integrating the foot core system into
rehabilitation for lower extremity injuries. Clin Sports Med 34: 347-361, 2015.
56. McNarry M, and Jones A. The influence of training status on the aerobic and anaerobic
responses to exercise in children: A review. Eur J Sport Sci 14: S57-S68, 2014.
57. Messier SP, Edwards DG, Martin DF, Lowery RB, Cannon DW, James MK, Curl WW, Read
HM, Jr., and Hunter DM. Etiology of iliotibial band friction syndrome in distance runners.
Med Sci Sports Exerc 27: 951-960, 1995.
58. Mikkola J, Rusko H, Nummela A, Pollari T, and Hakkinen K. Concurrent endurance and
explosive type strength training improves neuromuscular and anaerobic characteristics in
young distance runners. Int J Sports Med 28: 602-611, 2007.
59. Millet GP, Jaouen B, Borrani F, and Candau R. Effects of concurrent endurance and strength
training on running economy and VO(2) kinetics. Med Sci Sports Exerc 34: 1351-1359, 2002.
60. Moesch K, Elbe AM, Hauge ML, and Wikman JM. Late specialization: the key to success in
centimeters, grams, or seconds (cgs) sports. Scand J Med Sci Sports 21: e282-e290, 2011.
61. Mucha MD, Caldwell W, Schlueter EL, Walters C, and Hassen A. Hip abductor strength and
lower extremity running related injury in distance runners: A systematic review. J Sci Med
Sport 20: 349-355, 2017.
62. Myer GD, Faigenbaum AD, Chu DA, Falkel J, Ford KR, Best TM, and Hewett TE.
Integrative training for children and adolescents: techniques and practices for reducing sports-
related injuries and enhancing athletic performance. Phys Sports Med 39: 74-84, 2011.

63. Myer GD, Jayanthi N, DiFiori JP, Faigenbaum AD, Kiefer AW, Logerstedt D, and Micheli
LJ. Sports specialization, part II: alternative solutions to early sport specialization in youth
athletes. Sports Health 8: 65-73, 2016.
64. Myer GD, Kushner AM, Faigenbaum AD, Kiefer A, Kashikar-Zuck S, and Clark JF. Training
the developing brain, part I: cognitive developmental considerations for training youth. Curr
Sports Med Rep 12: 304-310, 2013.
65. Noakes TD. Implications of exercise testing for prediction of athletic performance: a
contemporary perspective. Med Sci Sports Exerc 20: 319-330, 1988.
66. Paavolainen L, Hakkinen K, Hamalainen I, Nummela A, and Rusko H. Explosive-strength
training improves 5-km running time by improving running economy and muscle power. J
Appl Physiol 86: 1527-1533, 1999.
67. Paavolainen LM, Nummela AT, and Rusko HK. Neuromuscular characteristics and muscle
power as determinants of 5-km running performance. Med Sci Sports Exerc 31: 124-130,
1999.
68. Pellegrino J, Ruby BC, and Dumke CL. Effect of plyometrics on the energy cost of running
and MHC and titin isoforms. Med Sci Sports Exerc 48: 49-56, 2016.
69. Piacentini MF, De Ioannon G, Comotto S, Spedicato A, Vernillo G, and La Torre A.
Concurrent strength and endurance training effects on running economy in master endurance
runners. J Strength Cond Res 27: 2295-2303, 2013.
70. Potdevin FJ, Alberty ME, Chevutschi A, Pelayo P, and Sidney MC. Effects of a 6-week
plyometric training program on performances in pubescent swimmers. J Strength Cond Res
25: 80-86, 2011.
71. Ramirez-Campillo R, Alvarez C, Henriquez-Olguin C, Baez EB, Martinez C, Andrade DC,
and Izquierdo M. Effects of plyometric training on endurance and explosive strength
performance in competitive middle- and long-distance runners. J Strength Cond Res 28: 97-
104, 2014.
72. Ramírez-Campillo R, Henríquez-Olguín C, Burgos C, Andrade DC, Zapata D, Martínez C,
Álvarez C, Baez EI, Castro-Sepúlveda M, and Peñailillo L. Effect of progressive volume-
based overload during plyometric training on explosive and endurance performance in young
soccer players. J Strength Cond Res 29: 1884-1893, 2015.
73. Ramírez-Campillo R, Meylan C, Alvarez C, Henríquez-Olguín C, Martínez C, Cañas-Jamett
R, Andrade DC, and Izquierdo M. Effects of in-season low-volume high-intensity plyometric
training on explosive actions and endurance of young soccer players. J Strength Cond Res 28:
1335-1342, 2014.
74. Reardon J. Optimal pacing for running 400-and 800-m track races. Am J Phys 81: 428-435,
2013.
75. Santos A, Marinho D, Costa A, Izquierdo M, and Marques M. The effects of concurrent
resistance and endurance training follow a specific detraining cycle in young school girls. J
Hum kinet 29: 93-103, 2011.
76. Santos AP, Marinho DA, Costa AM, Izquierdo M, and Marques MC. The effects of
concurrent resistance and endurance training follow a detraining period in elementary school
students. J Strength Cond Res 26: 1708-1716, 2012.
77. Schumann M, Mykkanen OP, Doma K, Mazzolari R, Nyman K, and Hakkinen K. Effects of
endurance training only versus same-session combined endurance and strength training on
physical performance and serum hormone concentrations in recreational endurance runners.
Appl Physiol Nutr Metabol 40: 28-36, 2015.
78. Scofield KL, and Hecht S. Bone health in endurance athletes: runners, cyclists, and
swimmers. Curr Sports Med Rep 11: 328-334, 2012.
79. Shaw AJ, Ingham SA, and Folland JP. The valid measurement of running economy in
runners. Med Sci Sports Exerc 46: 1968-1973, 2014.
80. Solomon ML, Briskin SM, Sabatina N, and Steinhoff JE. The pediatric endurance athlete.
Curr Sports Med Rep 16: 428-434, 2017.
81. Spurrs RW, Murphy AJ, and Watsford ML. The effect of plyometric training on distance
running performance. Eur J Appl Physiol 89: 1-7, 2003.

82. Steib S, Rahlf AL, Pfeifer K, and Zech A. Dose-response relationship of neuromuscular
training for injury prevention in youth athletes: a meta-analysis. Front Physiol 8: 920, 2017.
83. Tammelin T, Näyhä S, Hills AP, and Järvelin M-R. Adolescent participation in sports and
adult physical activity. Am J Prev Med 24: 22-28, 2003.
84. Tenforde AS, Kraus E, and Fredericson M. Bone stress injuries in runners. Phys Med Rehabil
Clin N Am 27: 139-149, 2016.
85. Thiel C, Foster C, Banzer W, and De Koning J. Pacing in Olympic track races: competitive
tactics versus best performance strategy. J Sports Sci 30: 1107-1115, 2012.
86. Turner AM, Owings M, and Schwane JA. Improvement in running economy after 6 weeks of
plyometric training. J Strength Cond Res 17: 60-67, 2003.
87. Unnithan V, Timmons J, Paton J, and Rowland T. Physiologic correlates to running
performance in pre-pubertal distance runners. Int J Sports Med 16: 528-533, 1995.
88. von Rosen P, Floström F, Frohm A, and Heijne A. Injury patterns in adolescent elite
endurance athletes participating in running, orienteering, and cross-country skiing. Int J
Sports Phys Ther 12: 822, 2017.
89. Warden SJ, Davis IS, and Fredericson M. Management and prevention of bone stress injuries
in long-distance runners. J Orthop Sports Phys Ther 44: 749-765, 2014.
90. Wilson JM, Marin PJ, Rhea MR, Wilson SM, Loenneke JP, and Anderson JC. Concurrent
training: a meta-analysis examining interference of aerobic and resistance exercises. J
Strength Cond Res 26: 2293-2307, 2012.
91. Wong P-l, Chamari K, and Wisløff U. Effects of 12-week on-field combined strength and
power training on physical performance among U-14 young soccer players. J Strength Cond
Res 24: 644-652, 2010.