"It inspired me to do something that would make people go 'wow' or "he's nuts'."
Mr Tennent is the Central North Island director for BNI (Business Network International) and runs chapters around the Bay of Plenty. BNI is a major sponsor of Hospice.
Mr Tennent has completed 17 events so far since starting the challenge in May with the T42 - a 42.2km trail run through the Central Plateau on his 54th birthday.
Many of the events are half-marathons, but some are longer including his first event and his final event - the Rotorua Marathon on May 3.
So far $45,351 has been pledged - money which will go to Hospices around New Zealand including Rotorua. Mr Tennent initially set a goal of $20,000 but would now like to raise $50,000.
Mr Tennent said he initially started running to lose weight. Seven years ago he was 112kg. He is now 90kg thanks to his running and his diet.
He is sponsored the entry fee for most events and people sponsor him per race.
He said the hardest part of the challenge was the travelling and the road runs. He prefers to run on the trails. If all the events had been road runs he would have given up but the trail runs were "magic".
"Two weeks ago when I was nearly dead (from exhaustion) I was standing at the highest point in the Hunua Ranges with views forever. We have an amazing country. A lot of it has trails that people don't know about."
He said he wasn't training much during the week as he was racing every weekend - competing in two half-marathons some weekends.
He has had to nurse a few injuries but Mr Tennent is determined to complete the challenge. "If I have to get round on crutches I will."
For more on the challenge or to donate go to www.52in52.org.nz.