Resistance Exercise Session: Damage protocol

The resistance exercise session designed to cause muscle damage consisted of three

exercises; 1) leg press exercise using a leg press machine (Universal, Cedar Rapids, IA,

USA); 2) leg extension exercise using a leg extension machine (Universal, Cedar

Rapids, IA, USA); and 3) leg flexion using a leg curl machine (Universal, Cedar

Rapids, IA, USA). All three exercises were designed to cause eccentric-induced damage

to the quadriceps and hamstring muscles (modified version of Brown et al., 1996;

Two weeks prior to the exercise session, strength assessments (1RM) were performed

on the left leg for each participant; the left leg would undergo the damage protocol,

while the contralateral leg was used as the control. Thus, only one leg needed to be

tested for muscle strength. The strength assessments consisted of the maximal weight

that could be lifted once (1RM) in the three of the exercises described above: leg press,

leg extension and leg flexion. The 1RM testing protocols followed that prescribed by

the National Strength and Conditioning Association (NSCA) (Baechle et al., 2000). In

short, the participant’s maximal lift was determined within no more than five single

repetition attempts following three progressively heavier warm up sets, thus causing

minimal damage if any. Participants were required to successfully lift each weight

before attempting a heavier weight. Each exercise was completed before the next

attempt. Exercise execution guidelines were defined and adhered to for the successful

completion of each lift (Baechle et al., 2000). A certified Strength and Conditioning

Specialist (NSCA) supervised all lifts.

3.1.4.1 Muscle-Damaging Exercises

After preliminary baseline testing, participants performed a series of resistance

exercises designed to elicit muscle damage of the knee extensor/flexor muscle groups.

Participants performed all exercises on the left leg while the contralateral leg acted as

the non-exercised control (rest). The first set of resistance exercises used a standard leg

press machine and required the participant to lower a mass equivalent to 120% of their

predetermined unilateral concentric 1RM. To perform an eccentric muscle action,

participants were seated with their entire leg at 90o relative to the torso, knees flexed to

~90o and feet rested on the foot pedals. Participants had their weight lifted for them by

the investigators, so that the legs finished at ~ 15o of flexion. The participant was then

foot pedal. From here the participant lowered the weight through an arc of ~75o (i.e.

back to ~90o). Each participant performed 40 (4 sets x 10 repetitions per set) eccentric

muscle actions using the leg press machine with 3 min rest between each set.

Participants were required to lower the weight at a fixed cadence (4 seconds) verbally

given by an investigator.

Participants then performed the same number of repetitions and sets using the same leg

on a standard knee flexion machine (figure 3.4). Again subjects were required to lower a

weight, lifted for them by the investigators; equivalent to 120% of their predetermined

unilateral concentric 1RM. Participants lied down on the apparatus, with their stomach

facing down, and their thigh slightly flexed ~15o relative to their torso and the knee at

~15o relative to the thigh. The participant remained in the lying position and had the

weight lifted by the investigators so that the knee was flexion at ~90o from horizontal.

Participants performed extension of the knee, and lowered the weight through an arc of

75o. The same lowering cadence was maintained to assure a relatively constant lowering

velocity.

The final exercise consisted of the same number of repetitions and sets using the same

leg on a standard knee extension machine. Participants sat on the apparatus with their

thigh at 90o relative to their torso and the knee at 90o relative to the thigh. The

participant remained seated and had the weight lifted by the investigators so that the

knee was extended at ~15o from horizontal. As mentioned previously, the weight was

equivalent to 120% of their predetermined unilateral concentric 1RM. Participants

performed flexion of the knee, and lowered the weight through an arc of 75o. Again the

and all participants were verbally encouraged during each exercise to maintain effort

throughout the range of motion.

If subjects were deviating from the required lowering cadence (as a result of fatigue),

then a brief (30s) rest was allowed during the set, so that the participant could complete

the set while still giving the appropriate effort. A maximum of two rests per set were

allowed. Each participant would have experienced some degree of fatigue during the

weight lowering, but all participants were able to complete the protocol. While it is

possible that the participants could have lowered the weight at slightly different

velocities when they were becoming fatigued; a constant timing during the lowering

motion was maintained by verbal timing instructions to minimise this. At completion of

the resistance exercises, participants rested for 10 minutes before performing the force

measurements (as described in Section 3.1.3.1) on both the exercised and non-exercised

leg and three vertical jumps (as described in Section 3.1.3.2).